MYLAN LABORATORIES INC
S-4, 1998-08-20
PHARMACEUTICAL PREPARATIONS
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<PAGE>
 
                                                Registration No. 333-_________

     As filed with the Securities and Exchange Commission on August 20, 1998.

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                                    FORM S-4
                             REGISTRATION STATEMENT
                                     Under
                           THE SECURITIES ACT OF 1933
                            MYLAN LABORATORIES INC.
             (Exact name of registrant as specified in its charter)

<TABLE>
<S>                              <C>                             <C>
      Pennsylvania                          2834                    25-1211621
(State or jurisdiction of        (Primary Standard Industrial   (I.R.S. Employer
incorporation or organization)   Classification Code Number)     Identification No.)
</TABLE>
                   130 Seventh Street, 1030 Century Building
                         Pittsburgh, Pennsylvania 15222
                                  412-232-0100
               (Address, including zip code and telephone number,
       including area code, of registrant's principal executive offices)

                                Mr. Milan Puskar
                            Mylan Laboratories Inc.
                   130 Seventh Street, 1030 Century Building
                         Pittsburgh, Pennsylvania 15222
                                  412-232-0100
(Name, address, including zip code and telephone number, including area code, of
                               agent for service)

                                   Copies to:
<TABLE>
<CAPTION>
<S>                                                                              <C>
                        John R. Previs                                                     Henry Lesser
          Buchanan Ingersoll Professional Corporation                            Heller Ehrman White & McAuliffe
                       One Oxford Centre                                              525 University Avenue
                 301 Grant Street, 20th Floor                                        Palo Alto, CA 94301-1800
                   Pittsburgh, PA 15219-1410                                        Telephone:  (650) 324-7000
                  Telephone:  (412) 562-8800                                        Telecopy:  (650) 324-0638
                   Telecopy:  (412) 562-1041
</TABLE>
Approximate date of commencement of the proposed sale of the securities to the
- ------------------------------------------------------------------------------
public: As soon as practicable after this Registration Statement becomes
- ------                                                                  
effective.

If the securities being registered on this Form are being offered in connection
with the formation of a holding company and there is compliance with General
Instruction G, check the following box. [ ]

If this Form is filed to register additional securities for an offering pursuant
to Rule 462(b) under the Securities Act, check the following box and list the
Securities Act registration statement number of the earlier effective
registration statement for the same offering. [ ]

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under
the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. [ ]

                        CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
==========================================================================================================================
    Title of Each                               Proposed Maximum         Proposed Maximum          Amount of Registration
 Class of Securities       Amount to be          Offering Price         Aggregate Offering                  Fee
 to be Registered(1)      Registered(2)            Per Share                 Price(3)
- --------------------------------------------------------------------------------------------------------------------------
<S>                    <C>                   <C>                     <C>                          <C>
Common Stock, $.50
par value............             6,791,216           N/A                  $175,398,145                   $51,743
==========================================================================================================================
</TABLE>

(1) This Registration Statement relates to Common Stock, par value $.50 per
    share ("Mylan Common Stock"), of the Registrant issuable to holders of
    Common Stock, par value $.01 per share ("Penederm Common Stock"), of
    Penederm Incorporated in connection with the merger of a wholly-owned
    subsidiary of the Registrant with and into Penederm Incorporated (the
    "Merger").

(2) The number of shares of Mylan Common Stock to be registered pursuant to this
    Registration Statement is based on the maximum number of shares of Mylan
    Common Stock issuable to holders of Penederm Common Stock and options to
    purchase shares of Penederm Common Stock in the Merger at an exchange ratio
    of 0.68 of a share of Mylan Common Stock in exchange for each share of
    Penederm Common Stock assuming the maximum number of shares of Penederm
    Common Stock to be acquired in the Merger for shares of Mylan Common Stock
    is 9,987,083.

(3) Estimated solely for purposes of calculating the registration fee pursuant
    to Rule 457(f)(1) of the Securities Act of 1933, based upon the estimated
    value of the shares of Penederm Common Stock to be acquired by Mylan in the
    Merger (based upon the average of the high and low sales prices of Penederm
    Common Stock on the Nasdaq National Market on August 17, 1998 of $17.5625
    per share).

                         ------------------------------

   The Registrant hereby amends this Registration Statement on such date or
dates as may be necessary to delay its effective date until the Registrant shall
file a further amendment which specifically states that this Registration
Statement shall thereafter become effective in accordance with Section 8(a) of
the Securities Act of 1933 or until this Registration Statement shall become
effective on such date as the Commission, acting pursuant to said Section 8(a),
may determine.
<PAGE>
 
                                [Penederm Logo]
                          320 Lakeside Drive, Suite A
                        Foster City, California   94404


                              ______________, 1998

Dear Stockholder:

   You are cordially invited to attend a Special Meeting of Stockholders of
Penederm Incorporated to be held at the Westin Hotel--San Francisco Airport,
located at 1 Bayshore Highway, Millbrae, California,  on [day], [date], 1998, at
[time], local time.

   At the Special Meeting, stockholders will vote on a proposal to approve and
adopt an Agreement and Plan of Merger which provides for the Company's
acquisition by Mylan Laboratories Inc. In this transaction, 0.68 of a share of
Mylan Common Stock will be exchanged for each Penederm share.

   Penederm's Board of Directors has unanimously decided that the Mylan
acquisition is in your best interests and unanimously recommends that you vote
"FOR" it at the Special Meeting.

   As I said in the joint press release announcing the proposed transaction on
June 24, 1998:

       "The Penederm Board is very pleased to be able to offer our stockholders
       this opportunity to exchange their shares for a significant equity
       investment in Mylan. We believe this transaction will enhance
       significantly Penederm's ability to pursue its product development and
       marketing plans."

   In the same joint press release, Mylan's CEO and President, Milan Puskar,
commented:

       "Penederm is an excellent strategic fit with Mylan. We expect their
       products and sales force to meaningfully add to our proprietary product
       line and marketing efforts. In addition, Penederm's current products
       under development offer significant opportunities for our combined
       shareholders. We see numerous opportunities to apply Penederm's patented
       drug delivery technology to products we have under development."

   Enclosed is our Proxy Statement relating to the Special Meeting, which also
constitutes Mylan's Prospectus covering the shares offered to you in exchange
for your Penederm shares. The Proxy Statement/Prospectus includes your Board's
recommendation in favor of the Mylan acquisition and our reasons for it, as well
as the background of the transaction, the conditions to closing and other
important information regarding the proposed transaction (including a
description of a stock option agreement with Mylan, voting agreements signed by
the Penederm directors and a new co-promotion agreement with Mylan relating to
our Avita(R) acne products).

   The enclosed Proxy Statement/Prospectus also includes the opinion of our
financial advisor, Lehman Brothers Inc., that, as of June 24, 1998 (the date the
Merger Agreement was signed) the exchange ratio of 0.68 of a Mylan share for
each Penederm share was, from a financial point of view, fair to the Penederm
stockholders. Please read the entire Proxy Statement/Prospectus, including the
Lehman Brothers opinion, carefully.

   Approval of the Mylan acquisition requires the favorable vote of a majority
of the outstanding Penederm shares. Your vote is important regardless of how
many shares you own. In order to ensure that your shares are represented at the
Special Meeting whether or not you are able to attend in person, we strongly
urge you to complete the enclosed proxy card promptly and return it in the
envelope provided.

   Please do not send us any of your stock certificates at this time. Following
the closing of the Mylan transaction, you will receive information about the
procedure for surrendering your Penederm stock certificates in exchange for
Mylan stock certificates.

                              Sincerely,

                              /s/ LLOYD H. MALCHOW

                              LLOYD H. MALCHOW
                              President and Chief Executive Officer


 
                           If you have any questions
                              or need assistance
                          completing your proxy card
                                 please call:
 
                           MACKENZIE PARTNERS, INC.
                               156 Fifth Avenue
                          New York, New York   10010
                         (212) 929-5500 (call collect)
                                              or
                         call toll-free (800) 322-2885
<PAGE>
 
                        [Logo of Penederm Incorporated]

                   NOTICE OF SPECIAL MEETING OF STOCKHOLDERS

To the Stockholders of

Penederm Incorporated:

   NOTICE IS HEREBY GIVEN that Penederm Incorporated ("Penederm") will hold a
special meeting of its stockholders on ____________, 1998, at _________, local
time, at the Westin Hotel--San Francisco Airport, 1 Bayshore Highway, Millbrae,
California (including any adjournments or postponements thereof, the "Special
Meeting"), for the following purposes:

        1. To consider and vote upon a proposal to approve and adopt an
    Agreement and Plan of Merger, dated as of June 24, 1998 (the "Merger
    Agreement"), by and among Penederm, Mylan Laboratories Inc., a Pennsylvania
    corporation ("Mylan"), and MLI Acquisition Corp., a Delaware corporation and
    a wholly-owned subsidiary of Mylan ("Merger Sub"), and the transactions
    contemplated thereby, including the merger of Merger Sub with and into
    Penederm (the "Merger"). In the Merger, each outstanding share of the Common
    Stock, par value $.01 per share, of Penederm ("Penederm Common Stock") will
    be converted into the right to receive 0.68 of a share of the common stock,
    par value $.50, of Mylan, and Penederm will become a wholly-owned subsidiary
    of Mylan.

        2. To transact such other business as may properly come before the
    Special Meeting.

   Only holders of record of Penederm Common Stock at the close of business on
_____________, 1998 (the "Record Date") will be entitled to notice of, and to
vote at, the Special Meeting. The affirmative vote of a majority of the
outstanding shares of Penederm Common Stock entitled to vote at the Special
Meeting is required to approve and adopt the Merger Agreement.

   If your shares are held of record by a broker, bank or other nominee, you
must instruct your broker, bank or other nominee on how to vote your shares, or
else your shares will not be voted. If you attend the Special Meeting, you may
vote your shares in person, which will revoke any previously executed proxy.
FAILURE TO RETURN A PROPERLY EXECUTED PROXY CARD OR TO VOTE AT THE SPECIAL
MEETING WILL GENERALLY HAVE THE SAME EFFECT AS A VOTE AGAINST THE MERGER.

                                    By Order of the Board of Directors


                                    Michael A. Bates
                                    Secretary

Foster City, California
             , 1998
- -------------


     YOUR VOTE IS VERY IMPORTANT. WHETHER OR NOT YOU EXPECT TO ATTEND THE
SPECIAL MEETING, PLEASE SIGN, DATE AND PROMPTLY RETURN THE ENCLOSED PROXY CARD
IN THE ENCLOSED POSTAGE PREPAID ENVELOPE.
<PAGE>
 
                             PENEDERM INCORPORATED
                                PROXY STATEMENT

                               _________________
     
                     PROSPECTUS OF MYLAN LABORATORIES INC.
                                 ______________

   This Proxy Statement/Prospectus is being furnished to holders of common
stock, par value $.01 per share ("Penederm Common Stock"), of Penederm
Incorporated, a Delaware corporation ("Penederm"), in connection with the
solicitation of proxies by the Board of Directors of Penederm (the "Penederm
Board") for use at the special meeting of stockholders of Penederm ("Penederm
Stockholders") to be held on ___________, 1998, at the Westin Hotel--San
Francisco Airport, 1 Bayshore Highway, Millbrae, California, at [time],
local time, and at any adjournments or postponements thereof (the "Special
Meeting").

   At the Special Meeting, Penederm Stockholders as of the close of business on
_____________, 1998 (the "Record Date") will consider and vote on the proposed
merger of MLI Acquisition Corp. ("Merger Sub"), a wholly-owned subsidiary of
Mylan Laboratories Inc., a Pennsylvania corporation ("Mylan"), with and into
Penederm (the "Merger"), whereby Penederm will become a wholly-owned subsidiary
of Mylan, pursuant to the terms of the Agreement and Plan of Merger, dated June
24, 1998, among Mylan, Merger Sub and Penederm (the "Merger Agreement"). If the
Merger is consummated, each outstanding share of Penederm Common Stock will be
converted into the right to receive 0.68 of a share (the "Exchange Ratio") of
common stock of Mylan, $.50 par value per share (the "Mylan Common Stock").

   This Proxy Statement/Prospectus also constitutes a Prospectus of Mylan with
respect to up to 6,791,216 shares of Mylan Common Stock to be issued in the
Merger in exchange for outstanding shares of Penederm Common Stock. Mylan Common
Stock is listed on the New York Stock Exchange ("NYSE") and trades under the
symbol "MYL." Penederm Common Stock is quoted on the Nasdaq National Market
("NASDAQ") and trades under the symbol "DERM."

   All information contained or incorporated by reference in this Proxy
Statement/Prospectus relating to Mylan and to the transactions described herein
has been supplied by Mylan, and all information contained or incorporated by
reference in this Proxy Statement/Prospectus relating to Penederm has been
supplied by Penederm.

   This Proxy Statement/Prospectus and the accompanying proxy card are first
being mailed to Penederm Stockholders on or about ___________, 1998.

   The Merger involves certain risks to Penederm Stockholders. See "RISK
FACTORS," beginning on page __.

THE SECURITIES TO BE ISSUED PURSUANT TO THIS PROXY STATEMENT/PROSPECTUS HAVE NOT
BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND EXCHANGE COMMISSION OR BY ANY
  STATE SECURITIES COMMISSION, NOR HAS THE COMMISSION OR ANY STATE SECURITIES
    COMMISSION PASSED UPON THE ACCURACY OR ADEQUACY OF THIS PROXY STATEMENT/
               PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A
                               CRIMINAL OFFENSE.
                            _______________________

      The date of this Proxy Statement/Prospectus is ______________, 1998.
                                        


Information contained herein is subject to completion or amendment. A 
registration statement relating to these securities has been filed with the 
Securities and Exchange Commission. These securities may not be sold, nor may 
offers to buy be accepted, prior to the time the registration statement becomes 
effective. This prospectus shall not constitute an offer to sell or the 
solicitation of an offer to buy, nor shall there be any sale of these securities
in any state in which such offer, solicitation or sale would be unlawful prior 
to registration or qualification under the securities laws of any such state.
<PAGE>
 
(Inside Front Cover)

                             AVAILABLE INFORMATION

   Mylan and Penederm are each subject to the informational requirements of the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), and in
accordance therewith file reports, proxy statements and other information with
the Securities and Exchange Commission (the "Commission"). These reports, proxy
statements and other information should be available for inspection at the
public reference facilities of the Commission located at Judiciary Plaza, 450
Fifth Street, N.W., Washington, D.C. 20549, and should also be available for
inspection and copying at prescribed rates at the Commission's Regional Offices
at 7 World Trade Center, Suite 1300, New York, New York 10048, and 500 West
Madison Street, Room 1400, Chicago, Illinois 60661. Copies of such material also
can be obtained from the Public Reference Section of the Commission, Washington,
D.C. 20549, at prescribed rates. The Commission also maintains an Internet web-
site at http://www.sec.gov that contains reports, proxy statements and other
information. Reports, proxy statements and other information concerning Mylan
can also be inspected at the offices of the NYSE, 20 Broad Street, New York, New
York 10005, on which Mylan Common Stock is listed. Reports, proxy statements and
other information concerning Penederm can be inspected at the Nasdaq National
Market, Operations, 1735 K Street, N.W., Washington D.C. 20006.

   Mylan has filed with the Commission a Registration Statement on Form S-4
(together with any amendments thereto, the "Registration Statement") under the
Securities Act of 1933, as amended (the "Securities Act"), with respect to the
Mylan Common Stock to be issued pursuant to the Merger Agreement. This Proxy
Statement/Prospectus does not contain all the information set forth in the
Registration Statement. Such additional information may be obtained from the
Commission's principal office in Washington, D.C.

THIS PROXY STATEMENT/PROSPECTUS INCORPORATES DOCUMENTS BY REFERENCE WHICH ARE
NOT PRESENTED HEREIN OR DELIVERED HEREWITH. SUCH DOCUMENTS ARE INCORPORATED BY
REFERENCE AT THE LOCATIONS IN THIS PROXY STATEMENT/PROSPECTUS WHERE SUCH
INFORMATION IS REQUIRED TO BE SET FORTH. THE DOCUMENTS RELATING TO MYLAN (OTHER
THAN EXHIBITS TO SUCH DOCUMENTS UNLESS SUCH EXHIBITS ARE SPECIFICALLY
INCORPORATED BY REFERENCE) ARE AVAILABLE TO ANY PERSON, INCLUDING ANY BENEFICIAL
OWNER TO WHOM THIS PROXY STATEMENT/PROSPECTUS IS DELIVERED, ON WRITTEN OR ORAL
REQUEST, WITHOUT CHARGE, TO MYLAN LABORATORIES INC., 130 SEVENTH STREET, 1030
CENTURY BUILDING, PITTSBURGH, PENNSYLVANIA 15222 (TELEPHONE NUMBER (412) 232-
0100), ATTENTION: PATRICIA SUNSERI, VICE PRESIDENT--INVESTOR AND PUBLIC
RELATIONS. THE DOCUMENTS RELATING TO PENEDERM (OTHER THAN EXHIBITS TO SUCH
DOCUMENTS UNLESS SUCH EXHIBITS ARE SPECIFICALLY INCORPORATED BY REFERENCE) ARE
AVAILABLE TO ANY PERSON, INCLUDING ANY BENEFICIAL OWNER TO WHOM THIS PROXY
STATEMENT/PROSPECTUS IS DELIVERED, ON WRITTEN OR ORAL REQUEST, WITHOUT CHARGE,
TO PENEDERM INCORPORATED, 320 LAKESIDE DRIVE, SUITE A, FOSTER CITY, CALIFORNIA
94404 (TELEPHONE NUMBER (650) 358-0100), ATTENTION: CORPORATE SECRETARY. IN
ORDER TO ENSURE TIMELY DELIVERY OF THE DOCUMENTS, ANY REQUESTS SHOULD BE MADE BY
________________, 1998.


                                       i
<PAGE>
 
                 INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

   The following documents previously filed by Mylan and Penederm, respectively,
with the Commission pursuant to the Exchange Act are incorporated herein by this
reference:

   1.  Mylan's Annual Report on Form 10-K for the fiscal year ended March 31,
1998 ("Mylan's 1998 Form 10-K"); Mylan's Quarterly Report on Form 10-Q for the
quarter ended June 30, 1998 ("Mylan's Most Recent 10-Q"); Mylan's Current
Report on Form 8-K dated June 30, 1998; and the description of Mylan Common
Stock in Mylan's Registration Statements filed pursuant to Section 12 of the
Exchange Act, and any amendment or report filed for the purpose of updating any
such description.

   2.  Penederm's Annual Report on Form 10-K for the fiscal year ended December
31, 1997 ("Penederm's 1997 Form 10-K"); Penederm's Quarterly Report on Form 10-Q
for the quarter ended March 31, 1998; Penederm's Quarterly Report on Form 10-Q
for the quarter ended June 30, 1998; and Penederm's Current Report on Form 8-K
dated June 29, 1998.

   In addition, the Merger Agreement and the Stock Option Agreement (as
hereinafter defined), copies of which are attached hereto as Appendix A and
Appendix B, respectively, are incorporated herein by reference.

   All documents filed by Mylan and Penederm pursuant to Section 13(a), 13(c),
14 or 15(d) of the Exchange Act subsequent to the date hereof and prior to the
termination of the offering of any securities offered hereby shall be deemed to
be incorporated by reference herein and to be a part hereof from the date any
such document is filed. Any statement contained in a document incorporated or
deemed to be incorporated by reference herein shall be deemed to be modified or
superseded for purposes hereof to the extent that a statement contained herein
(or in any other subsequently filed document that also is incorporated by
reference herein) modifies or supersedes such statement. Any statement so
modified or superseded shall be deemed, except as so modified or superseded, to
constitute a part hereof. All information appearing in this Proxy
Statement/Prospectus is qualified in its entirety by the information and
financial statements (including notes thereto) appearing in the documents
incorporated herein by reference, except to the extent set forth in the
immediately preceding statement.

                SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

   This Proxy Statement/Prospectus contains and incorporates by reference
certain statements that constitute "forward-looking statements" within the
meaning of the Private Securities Litigation Reform Act of 1995. These forward-
looking statements include all statements regarding the intent, belief or
current expectations regarding the matters discussed or incorporated by
reference in this Proxy Statement/Prospectus (including statements as to
"beliefs," "expectations," "anticipations," "intentions" or similar words) and
all statements which are not statements of historical fact. Such statements are
subject to risks, uncertainties and assumptions, including, but not limited to,
trends for the continued growth of the businesses of Mylan and Penederm, the
realization of anticipated revenues, profitability and cost synergies of the
combined companies and other risks and uncertainties described in "RISK
FACTORS."  Should one or more of these risks or uncertainties materialize or
should underlying assumptions prove incorrect, Mylan's or Penederm's actual
results, performance or achievements in 1998 and beyond could differ materially
from those expressed in, or implied by, such forward-looking statements.

   NO PERSON IS AUTHORIZED TO GIVE ANY INFORMATION OR TO MAKE ANY
REPRESENTATIONS WITH RESPECT TO THE MATTERS DESCRIBED IN THIS PROXY
STATEMENT/PROSPECTUS OTHER THAN THOSE CONTAINED HEREIN OR IN THE DOCUMENTS
INCORPORATED BY REFERENCE HEREIN. ANY INFORMATION OR REPRESENTATIONS WITH
RESPECT TO SUCH MATTERS NOT CONTAINED HEREIN OR THEREIN MUST NOT BE RELIED UPON
AS HAVING BEEN AUTHORIZED BY MYLAN OR PENEDERM. THIS PROXY STATEMENT/PROSPECTUS
DOES NOT CONSTITUTE AN OFFER TO SELL OR A SOLICITATION OF AN OFFER TO BUY
SECURITIES OR THE SOLICITATION OF ANY PROXY IN ANY JURISDICTION TO ANY PERSON TO
WHOM IT IS UNLAWFUL TO MAKE SUCH OFFER OR SOLICITATION IN SUCH JURISDICTION.
NEITHER THE DELIVERY OF THIS PROXY


                                      ii
<PAGE>
 
STATEMENT/PROSPECTUS NOR ANY SALE MADE HEREUNDER SHALL, UNDER ANY CIRCUMSTANCES,
CREATE ANY IMPLICATION THAT THERE HAS BEEN NO CHANGE IN THE AFFAIRS OF MYLAN OR
PENEDERM SINCE THE DATE HEREOF OR THAT THE INFORMATION IN THIS PROXY
STATEMENT/PROSPECTUS OR IN THE DOCUMENTS INCORPORATED BY REFERENCE HEREIN IS
CORRECT AS OF ANY TIME SUBSEQUENT TO THE DATE HEREOF OR THEREOF.

   As used herein, unless the context otherwise clearly requires, "Mylan" refers
to Mylan Laboratories Inc. and its consolidated subsidiaries, and "Penederm"
refers to Penederm Incorporated and its consolidated subsidiary.



                                      iii
<PAGE>
 
                               TABLE OF CONTENTS
                               -----------------

<TABLE>
<CAPTION>
                                                                            Page

<S>                                                                         <C>
AVAILABLE INFORMATION.........................................................Inside Front Cover
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE...............................................ii
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS.............................................ii
SUMMARY........................................................................................1
 Risk Factors..................................................................................1
 The Companies.................................................................................1
 The Special Meeting...........................................................................1
 The Merger....................................................................................2
 Selected Historical Consolidated Financial Data of Mylan......................................7
 Selected Historical Consolidated Financial Data of Penederm...................................7
 Selected Unaudited Pro Forma Combined Financial Data..........................................8
 Comparative Per-Share Data of Mylan and Penederm..............................................9
 Market Price Information.....................................................................10
RISK FACTORS..................................................................................12
 Fixed Exchange Ratio Despite Possible Changes in Stock Prices................................12
 Federal Trade Commission Investigation.......................................................12
 Uncertainties in Realizing Synergies of the Merger...........................................12
THE SPECIAL MEETING...........................................................................13
 Matters to Be Considered at the Special Meeting..............................................13
 Record Date and Quorum.......................................................................13
 Required Vote................................................................................13
 Proxies......................................................................................14
 Solicitation of Proxies......................................................................14
 Independent Auditors.........................................................................14
 Recommendation of Penederm Board.............................................................14
THE MERGER....................................................................................15
 Background of the Merger.....................................................................15
 Penederm's Reasons for the Merger; Recommendation of the Penederm Board......................19
 Opinion of Penederm's Financial Advisor......................................................22
 Mylan's Reasons for the Merger...............................................................27
 Regulatory Approvals.........................................................................27
 Interests of Certain Persons in the Merger...................................................28
 Accounting Treatment.........................................................................29
 Certain Federal Income Tax Consequences......................................................29
 Absence of Appraisal Rights..................................................................30
THE MERGER AGREEMENT AND THE RELATED AGREEMENTS...............................................30
 General......................................................................................30
 Consideration to Be Received in the Merger...................................................31
 Exchange of Shares...........................................................................31
 Treatment of Options.........................................................................32
 Representations and Warranties...............................................................32
 Conduct of Penederm's Business...............................................................33
 Exclusivity..................................................................................33
 Resales of Mylan Common Stock................................................................34
 Conditions to the Merger.....................................................................34
 Termination of the Merger Agreement..........................................................35
 Termination Fee; Expenses of the Merger......................................................35
 Benefit Plans................................................................................36
 The Stock Option Agreement...................................................................37
  The Option..................................................................................37
  Purchase Events.............................................................................38
  Mylan's Put Rights..........................................................................39
</TABLE>


                                      iv
<PAGE>
 
<TABLE>
<CAPTION>
<S>                                                                         <C>
  Mylan's Registration Rights..................................................................39
  Termination..................................................................................39
  Profit Limitation............................................................................39
 The Voting Agreements.........................................................................40
  Voting and Proxies...........................................................................40
  Prohibited Actions...........................................................................40
  Alternate Voting Agreement...................................................................40
  Other Provisions.............................................................................41
 Co-Promotion Agreements.......................................................................41
COMPARISON OF SHAREHOLDER RIGHTS...............................................................41
 Shareholder Rights Generally..................................................................41
 Shareholder Voting Rights.....................................................................42
 Shareholder Appraisal Rights..................................................................43
 Rights With Respect to Shares.................................................................44
 Fiduciary Duties of Directors.................................................................44
 Director and Officer Liability and Indemnification............................................44
 Charter Amendments............................................................................45
 Bylaw Amendments..............................................................................45
DESCRIPTION OF MYLAN CAPITAL STOCK.............................................................46
 Mylan Common Stock............................................................................46
 Mylan Preferred Stock.........................................................................46
 Special Considerations........................................................................46
UNAUDITED PRO FORMA COMBINED FINANCIAL INFORMATION.............................................47
EXPERTS........................................................................................52
LEGAL MATTERS..................................................................................52
STOCKHOLDER PROPOSALS..........................................................................52
APPENDIX A  AGREEMENT AND PLAN OF MERGER......................................................A-1
APPENDIX B  STOCK OPTION AGREEMENT............................................................B-1
APPENDIX C  VOTING AGREEMENTS.................................................................C-1
APPENDIX D  OPINION OF LEHMAN BROTHERS INC....................................................D-1
 
</TABLE>


                                       v
<PAGE>
 
                                     SUMMARY

   The following is a summary of certain important terms of the proposed Merger
and related information contained elsewhere in this Proxy Statement/Prospectus.
This summary is not intended to be complete and is qualified in its entirety by
reference to the more detailed information and financial statements, including
the notes thereto, contained elsewhere, or incorporated by reference, in this
Proxy Statement/Prospectus and the Appendices hereto. Except as otherwise
indicated, all financial information in this Proxy Statement/Prospectus is
presented in accordance with generally accepted accounting principles ("GAAP").
Penederm Stockholders are urged to read this Proxy Statement/Prospectus, the
Appendices hereto and the documents incorporated herein by reference in their
entirety. Unless otherwise defined herein, capitalized terms used in this
summary have the respective meanings ascribed to them elsewhere in this Proxy
Statement/Prospectus.

Risk Factors

   The completion of the Merger and an investment in Mylan Common Stock each
involve substantial risks. Before voting on the Merger and acquiring the
securities offered hereby, Penederm Stockholders should carefully consider the
information set forth in "RISK FACTORS" and other information contained or
incorporated by reference herein.

The Companies

<TABLE>
<S>                                           <C>
Mylan.......................................  Mylan is engaged in the development, licensing, manufacturing and
                                              marketing of numerous generic and proprietary finished
                                              pharmaceutical and wound care products. The principal executive
                                              offices of Mylan are located at 130 Seventh Street, 1030 Century
                                              Building, Pittsburgh, Pennsylvania 15222, and its telephone number
                                              at that address is (412) 232-0100.

Penederm....................................  Penederm is engaged in the development and commercialization of
                                              topically administered prescription dermatology products that use
                                              Penederm's proprietary drug delivery technology or drug compounds to
                                              achieve enhanced patient safety or clinical efficacy. The principal
                                              executive offices of Penederm are located at 320 Lakeside Drive,
                                              Foster City, California 94404, and its telephone number at that
                                              address is (650) 358-0100.

</TABLE> 

The Special Meeting

<TABLE> 
<S>                                           <C> 
Time, Date and Place........................  The Special Meeting will be held on __________________, 1998, at the
                                              Westin Hotel--San Francisco Airport, 1 Bayshore Highway, Millbrae,
                                              California, commencing at [time], local time.

Purpose of the Special Meeting..............  The purpose of the Special Meeting is (i) to consider and vote upon
                                              a proposal to approve and adopt the Merger Agreement and the
                                              transactions contemplated thereby, including the Merger, and (ii) to
                                              transact such other business as may properly be brought before the
                                              Special Meeting. See "THE SPECIAL MEETING--Matters to Be Considered
                                              at the Special Meeting."
Record Date; Shares Entitled to Vote;
Quorum......................................  Penederm Stockholders at the close of business on _____________,
                                              1998 (the "Record Date") are entitled to notice of and to vote at
                                              the Special Meeting. On the Record Date, there were ___________
                                              shares of Penederm Common Stock outstanding and entitled to vote.
                                              Each holder of record of shares of Penederm Common Stock on the
                                              Record Date is entitled to cast, either in person or by properly
                                              executed

</TABLE>
<PAGE>
 
<TABLE>
<S>                                           <C>

                                              proxy, one vote per share on the approval and adoption of
                                              the Merger Agreement and other matters, if any, properly submitted
                                              for the vote of Penederm Stockholders at the Special Meeting. See
                                              "THE SPECIAL MEETING."

                                              The presence, in person or by properly executed proxy, of the
                                              holders of stock representing a majority of the voting power of all
                                              outstanding shares of the Penederm Common Stock at the Special
                                              Meeting is necessary to constitute a quorum at the Special Meeting.
                                              See "THE SPECIAL MEETING."

Vote Required; Voting Agreements............  The approval by Penederm Stockholders of the Merger Agreement will
                                              require the affirmative vote of the holders of a majority of the
                                              outstanding shares of Penederm Common Stock entitled to vote
                                              thereon. As an inducement to Mylan to enter into the Merger
                                              Agreement, each of the directors of Penederm, who collectively hold
                                              approximately 3.8% of the outstanding Penederm Common Stock, has
                                              entered into an agreement with Mylan (the "Voting Agreements")
                                              pursuant to which each director has agreed to vote all of the shares
                                              of Penederm Common Stock beneficially owned by such director and all
                                              shares of Penederm Common Stock subsequently acquired (i) in favor
                                              of the Merger, the adoption by Penederm of the Merger Agreement and
                                              the approval of the other transactions contemplated by the Merger
                                              Agreement at any meeting of Penederm Stockholders at which such
                                              matters are considered and at every adjournment or postponement
                                              thereof and (ii) against any action or proposal that would impede,
                                              frustrate, prevent or nullify the Merger or the Merger Agreement.
                                              However, shares representing approximately 3.1% of the outstanding
                                              Penederm Common Stock are held by a director who has entered into an
                                              Alternate Voting Agreement permitting those shares to be
                                              distributed, as close to September 15, 1998 as possible, to the
                                              individual investors of the investment fund which owns such shares,
                                              and if such distribution occurs before the Penederm Stockholders
                                              vote on the Merger Agreement, there is no assurance as to how those
                                              shares will be voted. See "THE MERGER AGREEMENT AND THE RELATED
                                              AGREEMENTS--The Voting Agreements."
</TABLE> 

The Merger

<TABLE> 
<S>                                           <C> 
Merger Consideration........................  If the Merger is consummated, holders of Penederm Common Stock will
                                              receive, in exchange for each share of Penederm Common Stock they
                                              own, the right to receive 0.68 of a share of Mylan Common Stock.
                                              Fractional shares of Mylan Common Stock will not be issuable in
                                              connection with the Merger. Holders of Penederm Common Stock
                                              otherwise entitled to a fractional share will be paid the value of
                                              such fraction in cash determined as described herein under "THE
                                              MERGER AGREEMENT AND THE RELATED AGREEMENTS."  The Mylan Common
                                              Stock to be issued to Penederm Stockholders pursuant to Merger and
                                              any cash to be paid in lieu of fractional shares of Mylan Common
                                              Stock are referred to collectively as the "Merger Consideration."

                                              As soon as practicable after the filing of a certificate of merger
                                              with respect to the Merger in the office of the Delaware Secretary
                                              of State (the "Effective Time"), a letter of transmittal (including
                                              instructions

</TABLE>

                                       2
<PAGE>
 
<TABLE>
<CAPTION>
<S>                                           <C>

                                              setting forth the procedures for exchanging such
                                              holder's certificates representing Penederm Common Stock for the
                                              Merger Consideration payable to such holder pursuant to the Merger
                                              Agreement) will be sent to each holder of record, as of the
                                              Effective Time, of shares of Penederm Common Stock. Upon surrender
                                              of such certificates to the Exchange Agent (as defined herein)
                                              together with a duly completed and executed letter of transmittal,
                                              such holder will promptly receive the Merger Consideration for each
                                              share of Penederm Common Stock previously represented by the
                                              certificates so surrendered. See "THE MERGER AGREEMENT AND THE
                                              RELATED AGREEMENTS--Exchange of Shares."

Treatment of Existing Options...............  All rights under any stock option granted by Penederm pursuant to
                                              Penederm's Equity Incentive Plan, Employee Stock Option Plan,
                                              Consultant Stock Option Plan or Nonemployee Directors Stock Option
                                              Plan (collectively, the "Penederm Stock Option Plans") that remain
                                              unexercised immediately prior to the Effective Time will, together
                                              with the Penederm Stock Option Plans, be assumed by Mylan, and will
                                              thereafter represent the right to acquire that number of shares of
                                              Mylan Common Stock to which the holder would have been entitled
                                              pursuant to the Exchange Ratio if, immediately prior to the
                                              Effective Time, the holder had fully exercised the option and had
                                              been a stockholder of record of Penederm. The duration and other
                                              terms of the options will be the same as the original Penederm
                                              options, except that the references to Penederm in the Penederm
                                              Stock Option Plans will be deemed to be references to Mylan. The
                                              option price per share of Mylan Common Stock will be equal to the
                                              exercise price per share of Penederm Common Stock provided therein
                                              divided by the Exchange Ratio rounded up to the nearest cent. See
                                              "THE MERGER AGREEMENT AND THE RELATED AGREEMENTS--Treatment of
                                              Options."

Reasons for the Merger; Recommendation
of the Penederm Board.......................  The Penederm Board has unanimously determined that the Merger is in
                                              the best interests of Penederm and Penederm Stockholders and has
                                              approved the Merger Agreement. THE PENEDERM BOARD UNANIMOUSLY
                                              RECOMMENDS THAT THE PENEDERM STOCKHOLDERS VOTE IN FAVOR OF APPROVAL
                                              AND ADOPTION OF THE MERGER AGREEMENT AT THE SPECIAL MEETING. For a
                                              discussion of the factors considered by the Penederm Board in approving
                                              the Merger, see "THE MERGER--Penederm's Reasons for the Merger;
                                              Recommendation of the Penederm Board."

Opinion of Penederm's Financial
Advisor.....................................  Lehman Brothers Inc. ("Lehman Brothers") has delivered its written
                                              opinion to the Penederm Board that, as of June 24, 1998, the
                                              Exchange Ratio is fair, from a financial point of view, to the
                                              Penederm Stockholders.

                                              The full text of the written opinion of Lehman Brothers, setting
                                              forth assumptions made, procedures followed, other matters
                                              considered and review undertaken in connection with the opinion, is
                                              attached hereto as Appendix D and is incorporated herein by
                                              reference. Holders of Penederm Common Stock are urged to, and
                                              should, read such opinion in its entirety. See "THE MERGER--Opinion
                                              of Penederm's Financial Advisor" and Appendix D.

Interests of Certain Persons in the Merger..  For a discussion of the interests of certain executive officers and



</TABLE>

                                       3
<PAGE>
 
<TABLE>
<CAPTION>
<S>                                           <C>
                                              directors of Penederm in addition to their interests as Penederm
                                              Stockholders generally and information regarding Penederm Stock
                                              Options and other rights of certain members of the Penederm Board,
                                              see "THE MERGER--Interests of Certain Persons in the Merger."

Effective Time of the Merger................  The Effective Time will occur upon the filing of a Certificate of
                                              Merger with the Secretary of State of the State of Delaware or at
                                              such time thereafter as is provided in the Certificate of Merger.
                                              See "THE MERGER AGREEMENT AND THE RELATED AGREEMENTS."

Conditions to the Merger....................  The obligations of Mylan and Penederm to consummate the Merger are
                                              subject to the satisfaction of certain conditions, including,
                                              without limitation, obtaining the requisite approval of Penederm
                                              Stockholders, delivery to Mylan and Penederm of tax opinions, the
                                              continued accuracy of the representations and warranties contained
                                              in the Merger Agreement and the receipt of certain consents and
                                              approvals, including, without limitation, certain consents and
                                              approvals required under agreements to which Penederm is a party.
                                              Consummation of the Merger is also subject to compliance with
                                              Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended
                                              (the "HSR Act"). The notifications required under the HSR Act have
                                              been furnished to the Federal Trade Commission (the "FTC") and the
                                              Antitrust Division of the Department of Justice (the "Antitrust
                                              Division") and the parties have been granted early termination of
                                              the waiting period. However, the Antitrust Division and the FTC will
                                              continue to have the authority to challenge the Merger on antitrust
                                              grounds before or after the Merger is complete. See "THE
                                              MERGER--Regulatory Approvals" and "THE MERGER AGREEMENT AND THE
                                              RELATED AGREEMENTS--Conditions to the Merger."

Termination of the Merger Agreement.........  The Merger Agreement may be terminated at any time prior to the
                                              Effective Time under certain circumstances, including, among others:
                                              (i) by mutual written consent of Mylan and Penederm; (ii) by either
                                              Mylan or Penederm if an event or circumstance shall have occurred
                                              which has, or is reasonably expected to have, a Material Adverse
                                              Effect on the other or if there has been a Material Adverse Change
                                              with respect to the other; (iii) by either Mylan or Penederm if the
                                              Merger has not been effected prior to the close of business on
                                              November 30, 1998, subject to certain limitations; (iv) by either
                                              Mylan or Penederm if the requisite approval of Penederm Stockholders
                                              is not obtained; (v) by Mylan or Penederm if Penederm enters into a
                                              merger, acquisition or other agreement to effect a Superior Proposal
                                              (as defined below); and (vi) by Mylan if the Penederm Board, in
                                              breach of the Merger Agreement, withdraws or modifies its
                                              recommendation of the Merger, recommends a competing transaction or
                                              fails to recommend against a tender or exchange offer by a third
                                              party. See "THE MERGER AGREEMENT AND THE RELATED
                                              AGREEMENTS--Termination of the Merger Agreement."

</TABLE>

                                       4
<PAGE>
 
<TABLE>
<CAPTION>
<S>                                           <C>
Termination Fee; Expenses...................  Under certain circumstances, including a termination by Mylan if the
                                              Penederm Board withdraws or modifies its recommendation of the
                                              Merger or a termination by Penederm to execute a definitive
                                              agreement to implement another transaction, a termination of the
                                              Merger Agreement will require Penederm to pay Mylan a termination
                                              fee of $9 million (the "Termination Fee"). Other than expenses
                                              incurred in connection with the filing, printing and mailing of this
                                              Proxy Statement/Prospectus, which shall be borne equally between
                                              Mylan and Penederm, expenses incurred in connection with the Merger
                                              and Merger Agreement will be paid by the party incurring such
                                              expenses.

Stock Option Agreement......................  In connection with the execution of the Merger Agreement, Mylan and
                                              Penederm entered into the Stock Option Agreement pursuant to which
                                              Penederm granted Mylan an option (the "Mylan Option") to purchase up
                                              to 1,717,878 shares of Penederm Common Stock (the "Option Shares")
                                              (approximately 19.9% of the outstanding shares of Penederm Common
                                              Stock as of the date of the Merger Agreement) at an exercise price
                                              of $20.00 per share (the "Option Price"). The Mylan Option is
                                              exercisable only upon the occurrence of certain events and provides
                                              Mylan the right, under certain circumstances, to require Penederm to
                                              purchase for cash the unexercised portion of the Mylan Option. The
                                              Mylan Option was a condition to Mylan's entering into the Merger
                                              Agreement, and it might increase the likelihood of consummation of
                                              the Merger by discouraging competing offers for Penederm. Certain
                                              aspects of the Stock Option Agreement may have the effect of
                                              discouraging persons who may now, or prior to the Effective Time, be
                                              interested in acquiring all of or a significant interest in Penederm
                                              from considering or proposing such an acquisition, even if such
                                              persons were prepared to offer to pay consideration to Penederm
                                              Stockholders that had a higher current market price than the shares
                                              of Mylan Common Stock to be received for each share of Penederm
                                              Common Stock pursuant to the Merger Agreement. In addition, if Mylan
                                              were to become entitled to, and did, exercise the Mylan Option, such
                                              exercise could preclude a third party from acquiring Penederm in a
                                              transaction intended to be accounted for as a "pooling of
                                              interests," and the potential for such preclusion could further
                                              discourage competing offers for Penederm. Pursuant to the terms of
                                              the Stock Option Agreement, the aggregate maximum value of the
                                              Termination Fee and the Mylan Option is limited to $24 million. See
                                              "THE MERGER--Background of the Merger" and "--Penederm's Reasons for
                                              the Merger; Recommendation of the Penederm Board" and "THE MERGER
                                              AGREEMENT AND THE RELATED AGREEMENTS--The Stock Option Agreement."

                                              A copy of the Stock Option Agreement is attached as Appendix B to
                                              this Proxy Statement/Prospectus and is incorporated by reference
                                              herein.

Absence of Appraisal Rights.................  Penederm Stockholders are not entitled to exercise any appraisal
                                              rights under the Delaware General Corporation Law (the "DGCL") in
                                              connection with the Merger. See "THE MERGER--Absence of Appraisal
                                              Rights."

</TABLE>

                                       5
<PAGE>
 
<TABLE>
<CAPTION>
<S>                                           <C>
Certain Federal Income Tax
Consequences................................  It is expected that the Merger will constitute a reorganization
                                              under Section 368(a) of the Internal Revenue Code of 1986, as
                                              amended (the "Code"), for federal income tax purposes, and
                                              accordingly, no gain or loss will be recognized by Penederm
                                              Stockholders upon their exchange of Penederm Common Stock for Mylan
                                              Common Stock (except to the extent of any cash received in lieu of a
                                              fractional share interest in Mylan Common Stock). See "THE
                                              MERGER--Certain Federal Income Tax Consequences."

Accounting Treatment........................  The Merger is expected to be accounted for under the purchase method
                                              of accounting in accordance with GAAP. Under this method of
                                              accounting, the value of the consideration to be paid by Mylan in
                                              the Merger will be allocated to the assets acquired and the
                                              liabilities assumed based upon their estimated fair market values at
                                              the date of the consummation of the Merger. The results of
                                              operations of Penederm prior to the Merger will not be included in
                                              the reported results of the combined company thereafter. See "THE
                                              MERGER--Accounting Treatment."

Comparison of Shareholder Rights............  Upon consummation of the Merger, Penederm Stockholders will become
                                              shareholders of Mylan. There are certain material differences
                                              between the rights of holders of Mylan Common Stock and the rights
                                              of holders of Penederm Common Stock. These differences arise from
                                              the distinctions between the laws of the jurisdictions in which
                                              Mylan and Penederm are incorporated (Pennsylvania and Delaware,
                                              respectively) and the distinctions between the articles of
                                              incorporation and bylaws of Mylan and the certificate of
                                              incorporation and bylaws of Penederm. See "COMPARISON OF SHAREHOLDER
                                              RIGHTS."
</TABLE>

                                       6
<PAGE>
 
Selected Historical Consolidated Financial Data of Mylan


   The selected historical consolidated financial data for Mylan are based on
and derived from, and should be read in conjunction with, the historical
consolidated financial statements and the related notes thereto of Mylan. The
selected historical financial data for Mylan for each of the years ended March
31, 1996, 1995 and 1994 are derived from audited financial statements of Mylan
for those years. Mylan's consolidated balance sheets at March 31, 1998 and 1997,
and the consolidated statements of operations, shareholders' equity and cash
flows for each of the three years in the period ended March 31, 1998, were
audited by Deloitte & Touche LLP, independent auditors, and are included in
Mylan's 1998 Form 10-K which is incorporated by reference herein. The selected
historical consolidated financial data for Mylan should be read in conjunction
with Mylan's 1998 Form 10-K. The selected historical consolidated financial data
for Mylan set forth for each of the three month periods ended June 30, 1998 and
1997 are derived from the unaudited financial statements of Mylan which, in the
opinion of Mylan's management, contain all adjustments, consisting only of
normal recurring items, necessary to present fairly the selected financial data
for such periods. The results of operations for the three months ended June 30,
1998 may not be indicative of the results of operations to be expected for a
full year. See "INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE."

<TABLE>
<CAPTION>
                                                  Three months ended June 30,                    Year ended March 31,
                                                  ---------------------------   ----------------------------------------------------

                                                        1998           1997       1998       1997       1996       1995       1994
                                                                   (Amounts in thousands, except for per share data)
<S>                                                 <C>            <C>          <C>        <C>        <C>        <C>        <C>
Statement of Earnings Data:(1)
 Total Revenues                                     $166,718       $109,188     $555,423   $440,192   $392,860   $396,120   $251,773

                                                                                
 Net Earnings                                         34,182         16,598      100,777     63,127    102,325    120,869     73,067

                                                                                
Per Common Share:(2)
  Net Earnings-Basic                                    0.28           0.14         0.83       0.52       0.86       1.02       0.62

  Net Earnings-Diluted                                  0.28           0.13         0.82       0.51       0.85       1.01       0.61

  Dividends Declared(3)(4)                              0.04           0.04         0.16       0.16       0.15       0.19       0.10

                                                                                
 Shares Used in Net Earnings Per Common Share 
  Computation-Basic                                  122,295        122,065      122,094    121,926    119,530    118,963    118,423

 Shares Used in Net Earnings Per Common Share        124,078        123,039      123,043    122,727    120,706    119,912    119,502
  Computation-Diluted
</TABLE>

<TABLE>
<CAPTION>
                                                                June 30,                           March 31,
                                                        ---------------------   ----------------------------------------------------

                                                            1998       1997       1998       1997       1996       1995       1994
<S>                                                       <C>        <C>        <C>        <C>        <C>        <C>        <C>
Balance Sheet Data:(1)
 Working Capital                                          $381,711   $298,372   $358,752   $300,274   $330,733   $275,032   $191,647

 Total Assets                                              890,899    787,492    847,753    777,580    692,009    546,201    403,325

 Long-term Obligations (includes long-term debt and                            
  post-retirement compensation)                             26,417     32,936     26,218     32,593     18,002      7,122      4,609

                                                                               
                                                                               
 Shareholders' Equity                                      774,705    672,627    744,465    659,740    616,441    482,728    379,969

                                                                               
 Book Value Per Common Share                                  6.33       5.51       6.10       5.40       5.06       4.06       3.20

</TABLE>

(1) The acquisition of UDL Laboratories, Inc. is reflected in the financial data
    effective for the periods subsequent to February 28, 1996.

(2) The above financial information gives retroactive effect to the three-for-
    two stock split effective August 15, 1995.

(3) Mylan's current dividend program totals $.16 per share per year.

(4) For the year ended March 31, 1995, Mylan declared a special one-time
    dividend of $.067 per share.

Selected Historical Consolidated Financial Data of Penederm

   The selected consolidated financial data for Penederm are based on and
derived from, and should be read in conjunction with, the historical
consolidated financial statements and the related notes thereto of Penederm.
Penederm's historical consolidated balance sheets at December 31, 1997 and 1996,
and the consolidated statements of operations, stockholders' equity and cash
flows for each of the years ended December 31, 1995 through 1997, and notes
thereto, were audited by Ernst & Young LLP, independent auditors, and are
included in Penederm's 1997 Form 10-K which is incorporated by reference herein.
Penederm's consolidated statements of operations, stockholders' equity and cash
flows for the years ended December 31, 1993 and 1994, and notes thereto, were
audited by PricewaterhouseCoopers LLP, independent auditors. The selected
historical consolidated financial data for Penederm should be read in
conjunction with Penederm's 1997 Form 10-K. The selected historical unaudited

                                       7
<PAGE>
 
consolidated financial data for Penederm set forth for each of the six-month
periods ended June 30, 1998 and 1997 have been prepared on the same basis as the
selected historical information derived from such audited financial statements
and, in the opinion of Penederm's management, include all adjustments,
consisting only of normal recurring items, necessary to present fairly the
selected financial data for such periods. The results of operations for the six
months ended June 30, 1998 may not be indicative of the results of operations to
be expected for a full year. See "INCORPORATION OF CERTAIN DOCUMENTS BY
REFERENCE."

<TABLE>
<CAPTION>
                                                            Six months ended  June 30,            Year ended December 31,
                                                            -------------------------- ---------------------------------------------
                                                                 1998       1997         1997      1996     1995     1994     1993
                                                                         (Amounts in thousands, except for per share data)
<S>                                                           <C>         <C>          <C>       <C>      <C>      <C>      <C>
Statement of Operations Data:                                                                                              
 Total Revenues                                               $10,325     $ 4,904      $  9,005  $ 2,905  $ 5,401  $ 5,123  $ 1,378
                                                                                                                           
 Net (Loss)                                                    (2,570)     (3,839)      (12,717)  (7,643)  (5,036)  (4,993)  (5,539)

Per Common Share:(1)                                                                                                       
 Net (Loss)-Basic and Diluted                                   (0.31)      (0.49)        (1.59)   (1.05)   (0.70)   (0.71)   (4.61)

 Dividends Declared                                                --          --            --       --       --       --       --
 Shares Used in Net (Loss) Per Common Share
  Computation-Basic and Diluted                                 8,351       7,848         7,995    7,275    7,171    6,990    1,202
</TABLE>

<TABLE>
<CAPTION>
                                                                     June 30,                          December 31,
                                                               -------------------    ----------------------------------------------

                                                                  1998      1997       1997     1996      1995      1994      1993
<S>                                                              <C>      <C>         <C>      <C>      <C>       <C>       <C>
Balance Sheet Data:
 Working Capital                                                 $ 5,532  $11,236     $ 2,574  $ 5,710  $13,164   $17,307   $23,972
 Total Assets                                                     14,769   15,900      10,231   10,694   17,968    23,538    27,498
 Long-term Obligations                                                 5       20          10       28       54        15        70
 Stockholders' Equity                                              7,517   13,923       5,194    8,591   15,934    20,659    26,160
 Book Value Per Common Share                                        0.87     1.72        0.64     1.17     2.20      2.95      3.75
</TABLE>

(1)  Net (Loss) Per Common Share for the year ended December 31, 1993 has been
     retrospectively restated to apply Staff Accounting Bulletin (SAB) 98. SAB
     98 had no impact on any other year presented.

Selected Unaudited Pro Forma Combined Financial Data

   The following selected unaudited pro forma combined financial information has
been derived from and should be read in conjunction with the Unaudited Pro Forma
Combined Financial Statements and notes thereto included elsewhere in this
Proxy Statement/Prospectus. Mylan has a fiscal year ending on March 31, and
Penederm has a fiscal year ending on December 31. The following selected
unaudited pro forma combined financial information is based on the historical
consolidated balance sheets and related historical consolidated statements of
income of Mylan and Penederm as adjusted to give effect to the Merger using the
purchase method of accounting for business combinations, and for purposes of
such selected pro forma financial data, the Penederm financial information has
been recast to conform to the March 31 fiscal year used by Mylan. The
information set forth in the unaudited pro forma combined financial data should
be read in connection with the unaudited pro forma combined financial statements
and notes thereto appearing elsewhere herein. See "Unaudited Pro Forma Combined
Financial Information." The pro forma amounts are not necessarily indicative of
the results of operations or the combined financial position that would have
resulted had the Merger been consummated at the beginning of the fiscal year
presented, nor are they necessarily indicative of future results of operations
or financial position of Mylan.

                                       8
<PAGE>
 
<TABLE>
<CAPTION>
                                                                    Three months ended June 30, 1998    Year ended March 31, 1998
                                                                  ----------------------------------    -------------------------
                                                                         (Amounts in thousands, except for per share data)
<S>                                                                 <C>                                 <C>
Statement of Earnings Data:
 Total Revenues                                                                             $173,042                     $565,528
 
 Net Earnings(1)                                                                              33,838                       91,022
 Per Common Share:(1)
  Net Earnings-Basic                                                                            0.26                         0.71
  Net Earnings-Diluted                                                                          0.26                         0.71
  Dividends Declared                                                                            0.04                         0.16
 
 Shares Used in Net Earnings Per Common Share Computation-Basic                              128,082                      127,634
 Shares Used in Net Earnings Per Common Share Computation-Diluted                            130,200                      128,661
</TABLE>

<TABLE>
<CAPTION>
                                                                                        June 30, 1998
                                                                  --------------------------------------------------------
Balance Sheet Data:
<S>                                                                 <C>
 Working Capital                                                                                                  $384,743
 Total Assets                                                                                                      976,251
 Long-term Obligations (includes long-term debt and                                                                      
  post-retirement compensation)                                                                                     26,422
                                                                                                                         
                                                                                                                         
 Shareholders' Equity                                                                                              844,205
                                                                                                                         
 Book Value Per Common Share                                                                                          6.59   
</TABLE>

(1) As required by Article 11 of Regulation S-X under the Securities Exchange
    Act of 1934, the pro forma income statements exclude the nonrecurring
    charges for in-process research and development estimated at $145,000 and
    $900 of nonrecurring merger costs incurred by Penederm during the three
    months ended June 30, 1998. Had the pro forma income statements included
    these charges, Pro Forma Net (Loss) and Pro Forma Net (Loss) Per Common
    Share-Basic and Diluted would have been $(112,062) million, $(.87) for the
    three months ended June 30, 1998 and $(53,978) million, $(.42) for the year
    ended March 31, 1998.

Comparative Per-Share Data of Mylan and Penederm

   The following table presents: (i) the selected comparative per-share data for
each of Mylan and Penederm on an historical basis and (ii) the selected
unaudited pro forma combined comparative per-share data reflecting the
consummation of the Merger. The unaudited pro forma comparative per-share data
assume the Merger has been consummated at the beginning of the periods
presented. The unaudited pro forma data have been prepared giving effect to the
Merger under the purchase method of accounting.

   Under the purchase method of accounting, the total value of the Mylan Common
Stock issued in the Merger and the fair value of the vested stock options
granted by Penederm and assumed by Mylan are allocated among assets of Penederm
based upon their fair market values, and any value in excess of such fair
market values is recorded as goodwill.

   The Penederm pro forma equivalent amounts are presented with respect to each
set of pro forma information, and have been calculated by multiplying the
corresponding pro forma combined amounts per share of Mylan Common Stock by the
Exchange Ratio.

   The comparative per-share data presented herein are based on and derived
from, and should be read in conjunction with, the historical consolidated
financial statements and the related notes thereto of each of Mylan and Penederm
included in the documents incorporated by reference herein. See "INCORPORATION
OF CERTAIN DOCUMENTS BY REFERENCE." Pro forma amounts are not necessarily
indicative of the results of operations or the combined financial position that
would have resulted had the Merger been consummated at the beginning of the
fiscal year presented or indicative of the future earnings of Mylan.

                                       9
<PAGE>
 
<TABLE>
<CAPTION>
                                                               Three Months Ended                           Year Ended
                                                                 June 30, 1998                            March 31, 1998
                                                             -------------------                      -------------------
                                                                   (Amounts in thousands, except for per share data)
<S>                                                            <C>                                      <C>

Mylan Historical:

 Net Earnings-Basic                                                     $   0.28                                 $   0.83
 Net Earnings-Diluted                                                       0.28                                     0.82
 Dividends Declared                                                         0.04                                     0.16
 Book Value                                                                 6.33                                     6.10
 Shares Used in Net Earnings Per Common Share                            122,295                                  122,094
  Computation-Basic
 Shares Used in Net Earnings Per Common Share                            124,078                                  123,043
  Computation-Diluted

Penederm Historical:

 Net (Loss)-Basic                                                       $  (0.14)                                $  (1.55)
 Net (Loss)-Diluted                                                        (0.14)                                   (1.55)
 Dividends Declared                                                           --                                       --
 Book Value                                                                 0.87                                     0.58
 Shares Used in Net (Loss) Per Common Share                                8,511                                    8,147
  Computation-Basic and Diluted

Mylan Pro Forma:(1)(4)  

 Net Earnings-Basic                                                     $   0.26                                 $   0.71
 Net Earnings-Diluted                                                       0.26                                     0.71
 Dividends Declared                                                         0.04                                     0.16
 Book Value                                                                 6.59                                      N/C
 Shares Used in Net Earnings Per Common Share                            128,082                                  127,634
  Computation-Basic
 Shares Used in Net Earnings Per Common Share                            130,200                                  128,661
  Computation-Diluted

Penederm Equivalent Pro Forma:(2)(4)  

 Net Earnings-Basic                                                     $   0.18                                 $   0.48
 Net Earnings-Diluted                                                       0.18                                     0.48
 Dividends Declared                                                         0.03                                     0.11
 Book Value                                                                 4.49                                      N/C
 Shares Used in Net Earnings Per Common Share                            188,356                                  187,697
  Computation-Basic(3)
 Shares Used in Net Earnings Per Common Share                            191,471                                  189,207
  Computation-Diluted(3)
</TABLE>
- ----------------
(1) The pro forma information was calculated by combining the historical amounts
    from Mylan and Penederm after considering the pro forma adjustments divided
    by the sum of Mylan's historical share information and the additional shares
    of Mylan Common Stock estimated to be issued upon consummation of the
    Merger.  Pro forma book value per share is presented for the interim period
    only.

(2) Represents the pro forma information (as calculated in note 1) adjusted to
    reflect the value of one share of Penederm Common Stock.

(3) Penederm equivalent pro forma shares represent the Mylan pro forma shares
    divided by the conversion ratio of .68.

(4) Had the pro forma income statements included the nonrecurring charges for
    in-process research and development estimated at $145,000 and $900 of
    nonrecurring merger costs incurred by Penederm during the three months ended
    June 30, 1998, Pro Forma Net (Loss) Per Common Share-Basic and Diluted would
    have been $(.87) for the three months ended June 30, 1998 and $(.42) for the
    year ended March 31, 1998.

   Additionally, Penederm equivalent Pro Forma Net (Loss) Per Common Share-Basic
   and Diluted would have been $(.59) for the three months ended June 30, 1998
   and $(.29) for the year ended March 31, 1998.

N/C = Not computed.

Market Price Information

   Mylan Common Stock is traded on the NYSE under the symbol "MYL." The table
below sets forth for the periods indicated the high and low closing sale prices
per share of Mylan Common Stock and the dividends paid per share of Mylan Common
Stock. For current price information with respect to the Mylan Common Stock,
Penederm Stockholders are urged to consult publicly available sources. No
assurance can be given as to future prices of, or markets for, Mylan Common
Stock. See "RISK FACTORS--Fixed Exchange Rate Despite Possible Changes in Stock
Prices" and "--Federal Trade Commission Investigation."

                                       10
<PAGE>
 
<TABLE>
<CAPTION>
                                              Mylan Common Stock
                                              ------------------
                                         High        Low       Dividends
                                     -----------------------------------
<S>                                    <C>         <C>         <C>
Fiscal Year Ended March 31, 1997
First Quarter........................    $21.63      $16.25         $.04
Second Quarter.......................     17.50       14.25          .04
Third Quarter........................     17.50       14.00          .04
Fourth Quarter.......................     18.25       14.38          .04
Fiscal Year Ended March 31, 1998
First Quarter........................     16.88       11.50          .04
Second Quarter.......................     24.75       14.63          .04
Third Quarter........................     25.25       17.44          .04
Fourth Quarter.......................     24.31       17.06          .04
Fiscal Year Ending March 31, 1999
First Quarter........................     32.75       22.06          .04
Second Quarter
  (through August 19, 1998)..........     35.13       24.50          .04
</TABLE>

   Penederm Common Stock is quoted on NASDAQ and traded under the symbol "DERM."
The table below sets forth for the periods indicated the high and low sales
prices per share of Penederm Common Stock. For current price information with
respect to the Penederm Common Stock, Penederm Stockholders are urged to consult
publicly available sources. Penederm has never declared or paid any cash
dividends on Penederm Common Stock.

<TABLE>
<CAPTION>
                                                                           Penederm Common Stock
                                                                           ----------------------
                                                              High                                             Low
                                            ---------------------------------------------       ----------------------------------
<S>                                           <C>                                                 <C>
Fiscal Year Ended December 31, 1996
First Quarter........................                       $18.25                                              $10.75
                                                            ------                                              ------
Second Quarter.......................                        17.75                                               12.50
                                                            ------                                              ------
Third Quarter........................                        16.50                                                4.88
Fourth Quarter.......................                        12.50                                                6.75
Fiscal Year Ended December 31, 1997
First Quarter........................                        17.25                                               10.50
Second  Quarter......................                        13.50                                               10.00
Third  Quarter.......................                        14.88                                               10.00
Fourth  Quarter......................                        13.88                                                9.13
Fiscal Year Ending December 31, 1998
First  Quarter.......................                        13.00                                                9.56
Second Quarter.......................                        21.31                                               10.25
Third Quarter
  (through August 19, 1998)..........                        23.50                                               16.25
</TABLE>

   Set forth below are the last reported sale prices of the Mylan Common Stock
and the Penederm Common Stock on June 23, 1998, the last trading day prior to
the public announcement of the Merger Agreement, and on August 19, 1998, the
last trading day prior to the date of this Proxy Statement/Prospectus, as well
as the equivalent pro forma sale prices of the Penederm Common Stock on such
dates, as determined by multiplying the applicable last reported sale price of
the Mylan Common Stock on the NYSE by the Exchange Ratio.

<TABLE>
<CAPTION>
                                                                     Penederm
                                  Mylan Common Stock               Common Stock               Penederm Equivalent
                                  ------------------               ------------               -------------------
<S>                               <C>                              <C>                         <C>
June 23, 1998..............             $32.19                         $15.75                        $21.88
August 19, 1998............             $30.625                        $20.25                        $20.825
</TABLE>

                                       11
<PAGE>
 
                                   RISK FACTORS

   The following factors should be considered carefully by the Penederm
Stockholders in evaluating whether to approve and adopt the Merger Agreement.
These factors should be considered in conjunction with any additional risk
factors in documents incorporated by reference in this Proxy
Statement/Prospectus and any other information included or incorporated by
reference herein, including in conjunction with forward-looking statements made
herein. See "INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE."

   Fixed Exchange Ratio Despite Possible Changes in Stock Prices. The Exchange
Ratio establishing the percentage of a share of Mylan Common Stock into which
each share of Penederm Common Stock will be converted is a fixed ratio.
Accordingly, the Exchange Ratio will not be adjusted in the event of any
increase or decrease in the price of Mylan Common Stock or the price or value of
Penederm Common Stock. In addition, neither party has the right to terminate the
Merger Agreement or elect not to consummate the Merger as a result of changes in
the prices of such stocks. The price of Mylan Common Stock at the Effective Time
or at any time thereafter may vary from its price at the date of execution of
the Merger Agreement, the date of this Proxy Statement/Prospectus or the date of
the Special Meeting. Such variations may be the result of changes in the
business, operations or prospects of Mylan or Penederm, market assessments of
the likelihood that the Merger will be consummated and the timing thereof,
regulatory considerations, general market and economic conditions and other
factors. Because the Effective Time may occur at a date later than the Special
Meeting, there can be no assurance that the price of Mylan Common Stock on the
date of the Special Meeting will be indicative of its price at the Effective
Time or at any time thereafter. The Effective Time will occur as soon as
practicable following the Special Meeting and the satisfaction or waiver of the
other conditions set forth in the Merger Agreement. Penederm Stockholders are
urged to obtain current market quotations for Mylan Common Stock. See "THE
MERGER AGREEMENT AND THE RELATED AGREEMENTS--Consideration to Be Received in the
Merger" and "--Conditions to the Merger." For a discussion of the risk of
unusual volatility in the market price of Mylan Common Stock, see "--Federal
Trade Commission Investigation." For information with respect to the market
prices of Penederm Common Stock and Mylan Common Stock during certain periods
and on certain dates, see "SUMMARY--Market Price Information."

   Federal Trade Commission Investigation. Mylan has received from the Federal
   --------------------------------------                                     
Trade Commission (the "FTC") a non-public subpoena requiring Mylan to provide
certain information in connection with a pending FTC investigation to determine
whether Mylan or others had engaged in unlawful activities restricting
competition in the manufacture or sale of active pharmaceutical ingredients or
pharmaceutical products.  Four states have also notified Mylan that they are
conducting their own investigations.  Mylan understands that the FTC
investigation was prompted by price increases initiated by it on certain of its
products.  However, Mylan does not know whether the focus of the investigation
is Mylan's price increases or is (or might lead to) a broader investigation into
pricing in the generic drug industry generally.  Mylan's Most Recent 10-Q (see
"INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE") reported that Mylan is
cooperating fully with the FTC and is providing all information requested by it.
As with all governmental investigations, the process is inherently uncertain.
However, Mylan has stated in Mylan's Most Recent 10-Q that it believes that its
management has acted properly and in full compliance with the Federal Trade
Commission Act and all other laws and regulations governing trade and
competition in the marketplace, and that the ultimate resolution of the matter
will not have a material adverse effect on Mylan's financial position, results
of operations or cash flows. Mylan's Most Recent 10-Q contains additional 
discussion relating to the FTC investigation.

   Uncertainty as to the effects or outcome of the FTC investigation is one of
many factors that can adversely affect the market price of Mylan Common Stock.
In addition, public reports about the investigation that may appear from time to
time in the future (whether or not correct) may cause the market price of Mylan
Common Stock to decline.  As a consequence, the FTC investigation, until
resolved, may cause unusual volatility in the market price of Mylan Common Stock
irrespective of other factors that could positively or negatively affect such
market price, including the possible continuation of the volatility that has
characterized stock prices in the generic drug sector and the stock market
generally during the period following the public announcement of the Merger on
June 24, 1998. See "SUMMARY--Market Price Information."

   Uncertainties in Realizing Synergies of the Merger. In determining that the
Merger is advisable and in the best interests of Penederm Stockholders, the
Penederm Board considered, among other things, special opportunities

                                       12
<PAGE>
 
for synergistic benefits to be realized from a combination of Penederm and
Mylan, including those enumerated in paragraph 2 under "THE MERGER--Penederm's
Reasons for the Merger; Recommendation of the Penederm Board." The realization
of these synergistic opportunities presents significant management challenges.
There can be no assurance that such opportunities will be successfully realized,
realized as expeditiously as currently expected or realized in any meaningful
way. Moreover, there can be no assurance of the extent to which any synergies
will be achieved. See "THE MERGER--Penederm's Reasons for the Merger;
Recommendation of the Penederm Board."

                               THE SPECIAL MEETING

   The Special Meeting will be held on _________, 1998, at [time], local time,
at the Westin Hotel--San Francisco Airport, 1 Bayshore Highway, Millbrae,
California. This Proxy Statement/Prospectus is also being used in the
solicitation of proxies from the Penederm Stockholders by the Penederm Board for
use at the Special Meeting.

   This Proxy Statement/Prospectus is first being mailed to Penederm
Stockholders, and the accompanying forms of proxies are first being mailed on or
about _______________, 1998.

Matters to Be Considered at the Special Meeting

   At the Special Meeting, holders of Penederm Common Stock will (i) consider
and vote upon the approval and adoption of the Merger Agreement and (ii)
transact such other business as may properly come before the Special Meeting.

Record Date and Quorum

   The Penederm Board has fixed ________________, 1998 as the Record Date for
the determination of the Penederm Stockholders entitled to notice of and to vote
at the Special Meeting. Accordingly, only Penederm Stockholders of record on the
Record Date will be entitled to notice of and to vote at the Special Meeting. As
of _______________, 1998, there were _______________ shares of Penederm Common
Stock outstanding, entitled to vote and held by _______________ holders of
record. Each Penederm Stockholder of record on the Record Date is entitled to
cast one vote per share on each proposal properly submitted for the vote of the
Penederm Stockholders, either in person or by properly executed proxy, at the
Special Meeting. The presence, in person or by properly executed proxy, of the
holders of a majority of the outstanding shares of Penederm Common Stock
entitled to vote is necessary to constitute a quorum at the Special Meeting.

Required Vote

   The approval by Penederm Stockholders of the Merger Agreement will require
the affirmative vote of the holders of a majority of the outstanding shares of
Penederm Common Stock entitled to vote thereon. A failure to vote or an
abstention or a broker non-vote will have the same legal effect as a vote by a
Penederm Stockholder against the approval of the Merger and approval and
adoption of the Merger Agreement.

   Each Penederm director has advised Penederm that he intends to vote or direct
the vote of all shares of Penederm Common Stock over which he has voting control
FOR approval of the Merger Agreement pursuant to the terms of the voting
agreements entered into between Mylan and each such director at the time of the
execution of the Merger Agreement. Directors of Penederm own beneficially
approximately 3.8% of the outstanding shares of Penederm Common Stock. See "THE
MERGER AGREEMENT AND THE RELATED AGREEMENTS--The Voting Agreements."

   As of _______________, 1998, neither Mylan nor any of its subsidiaries owned
any shares of Penederm Common Stock.

                                       13
<PAGE>
 
Proxies

   This Proxy Statement/Prospectus is being furnished to Penederm Stockholders
in connection with the Special Meeting. In addition, it is being used in the
solicitation of proxies (individually a "Solicited Proxy" and collectively the
"Solicited Proxies") from the Penederm Stockholders for use at the Special
Meeting.

   All shares of Penederm Common Stock that are entitled to vote and are
represented at the Special Meeting by properly executed Solicited Proxies
received prior to or at the Special Meeting, and not revoked, will be voted at
the Special Meeting in accordance with the instructions indicated on such
Solicited Proxies. If no instructions are indicated, such Solicited Proxies will
be voted FOR approval of the Merger and approval and adoption of the Merger
Agreement.

   If any other matters are properly presented at the Special Meeting for
consideration, including consideration of a motion to adjourn the Special
Meeting to another time and/or place (including for the purpose of soliciting
additional Solicited Proxies), unless otherwise indicated on such Solicited
Proxies, the person named in the enclosed forms of Solicited Proxies and acting
thereunder will have discretion to vote on such matters in accordance with his
best judgment.

   Any Solicited Proxy given pursuant to this solicitation may be revoked by the
person giving it at any time before it is voted. Solicited Proxies may be
revoked by (i) filing with the Secretary of Penederm, at or before the taking of
the vote at the Special Meeting, a written notice of revocation bearing a later
date than the Solicited Proxy; (ii) duly executing a later-dated proxy relating
to the same shares and delivering it to the Secretary of Penederm before the
taking of the vote at the Special Meeting; or (iii) attending the Special
Meeting and voting in person (although attendance at the Special Meeting will
not in and of itself constitute a revocation of the Solicited Proxy). Any
written notice of revocation or subsequent proxy should be sent so as to be
delivered to Michael A. Bates, Secretary, Penederm Incorporated, 320 Lakeside
Drive, Foster City, California 94404, or hand-delivered to the Secretary of
Penederm, at or before the taking of the vote at the Special Meeting.

Solicitation of Proxies

   The entire cost of soliciting the proxies from Penederm Stockholders will be
borne by Penederm, except that Mylan and Penederm have each agreed to pay one
half of the printing and mailing costs associated with this Proxy
Statement/Prospectus. See "THE MERGER AGREEMENT AND THE RELATED AGREEMENTS--
Termination Fee; Expenses of the Merger." In addition to the solicitation of the
proxies by mail, MacKenzie Partners, Inc., a proxy solicitation firm, will
assist Penederm in soliciting proxies for the meeting and will be paid a fee of
$7,500 plus out-of-pocket expenses. Penederm will also request banks, brokers
and other record holders to send proxies and proxy material to the beneficial
owners of the stock and secure their voting instructions, if necessary. Penederm
will reimburse such record holders for their reasonable expenses in so doing.
Proxies may also be solicited personally or by telephone or other means of
communication by directors, officers and regular employees of Penederm without
additional compensation therefor.

Independent Auditors

   One or more representatives of Ernst & Young LLP, independent auditors for
Penederm, are expected to be present at the Special Meeting and will have an
opportunity to make a statement if they desire to do so and will be available to
respond to appropriate questions.

Recommendation of Penederm Board

   The Penederm Board has unanimously approved the Merger Agreement and
recommended a vote FOR approval of the Merger Agreement by the Penederm
Stockholders.

                PENEDERM STOCKHOLDERS SHOULD NOT SEND ANY STOCK
                      CERTIFICATES WITH THEIR PROXY CARDS.

                                       14
<PAGE>
 
                                    THE MERGER

Background of the Merger

   In early 1997, the Chief Executive Officer of Bertek Pharmaceuticals, Inc.
("Bertek"), a wholly-owned subsidiary of Mylan engaged in the development and
sale of proprietary pharmaceutical products, approached Penederm to explore the
possibility of a collaboration with respect to Penederm's proprietary
dermatology products. Following additional intermittent discussion, in March
1997, Bertek and Penederm signed a confidentiality agreement providing for
Penederm to furnish to Bertek proprietary information regarding certain of
Penederm's products with a view to a possible product development and
commercialization collaboration. Further discussion on that subject took place
in June 1997 during a visit to Penederm by Bertek's Chief Executive Officer and
Chief Financial Officer.

   During the next several months, discussions regarding a possible product
development collaboration continued intermittently. Lloyd H. Malchow, Penederm's
President and Chief Executive Officer, and Penederm's Vice President for
Business Development led the discussions on behalf of Penederm, and in addition
to the two senior executives of Bertek, the discussions also involved Roderick
P. Jackson, Mylan's Senior Vice President. By October 1997, the discussions had
focused on a proposed co-promotion agreement (the "Mentax(R) Co-Promotion
Agreement") under which Bertek would promote Penederm's Mentax(R) topical
prescription anti-fungal product to primary care physicians in the United
States. There was also some discussion of the possibility that, in conjunction
with the execution of the Mentax(R) Co-Promotion Agreement, Mylan would make an
equity investment in Penederm in the range of $3$10 million. These proposed
arrangements were approved by the Penederm Board at a regular meeting on October
13, 1997 and were discussed at a meeting among representatives of Penederm,
Bertek and Mylan on October 16, 1997.

   During the next several weeks, Penederm and Bertek finalized the terms of the
Mentax(R) Co-Promotion Agreement while deferring discussion of a possible equity
investment by Mylan in Penederm. The Mentax(R) Co-Promotion Agreement was signed
on December 2, 1997 and jointly announced by Penederm and Mylan on December 9,
1997.

   At a meeting held on December 2, 1997 among representatives of Penederm,
Bertek and Mylan, the possibility of Mylan making a $3-$10 million equity
investment in Penederm was again discussed, and Mylan also expressed interest in
a broader relationship with Penederm, including not only a possible co-promotion
arrangement for Penederm's Avita(R) cream and gel acne products but also an
acquisition of Penederm. Mr. Malchow indicated that Penederm was interested in
discussing the possible equity investment as a means of financing Penederm's
operations until Penederm began to generate positive cash flow from product
revenues. However, he advised that Penederm was not in a position to discuss any
broader collaboration at that time because the Penederm Board had scheduled
strategic planning sessions with senior management for December 1997 and
February 1998 and, pending the outcome of those sessions, Penederm was focused
on completing its financing arrangements and continuing to implement its
internal business plan, which called for continued dedication to product
development and marketing.

   At a regularly scheduled meeting held on December 15, 1997, the Penederm
Board received a presentation from Penederm's senior management regarding
Penederm's strategic alternatives for its future direction, including the
possibility of changing Penederm's product development and commercialization
strategies, seeking a partner for a strategic "merger of equals," selling
Penederm and continuing to operate under the current business plan. Each of
these possibilities was discussed as a general matter but no decision was made
and no action was authorized. The Penederm Board decided to resume the
discussion at its regularly scheduled February 1998 meeting. The Penederm Board
also discussed Penederm's capital needs and financing alternatives, and
authorized Mr. Malchow to continue exploring a sale of a minority equity
position in Penederm to one of Penederm's product collaboration partners
(including Mylan).

   During the next few weeks, Penederm and Mylan again discussed a possible
equity investment by Mylan in Penederm. However, the companies could not agree
on mutually acceptable terms, the discussions were discontinued and on January
21, 1998, Penederm entered into definitive agreements with another party (not
one of Penederm's product collaboration partners) for a $10 million equity line
of credit.

                                       15
<PAGE>
 
   On February 10, 1998, at a meeting between Messrs. Malchow and Jackson, Mr.
Jackson expressed Mylan's interest in acquiring Penederm for a price of up to
$18.00 per share, subject to due diligence and definitive documentation. Mr.
Malchow undertook to convey Mylan's interest to the Penederm Board at its
regularly scheduled February 1998 meeting.

   At a regularly scheduled meeting of the Penederm Board held on February 25,
1998, Mr. Malchow advised the Penederm Board of his conversation with Mr.
Jackson. After discussing the matter and conferring with Penederm's outside
counsel, Heller Ehrman White & McAuliffe ("HEWM"), the Penederm Board
unanimously decided to engage a nationally recognized investment banking firm to
assist in the Penederm Board's evaluation of Penederm's strategic alternatives,
including an independent analysis of senior management's long-term business
plan, an examination of equity financing possibilities and an assessment of the
possibility of Penederm pursuing a business combination. The Penederm Board also
decided that, unless and until it determined otherwise after the evaluation was
completed, Penederm was not for sale and Penederm's senior management should
continue to focus on implementing Penederm's own business plan. However, the
Penederm Board concluded that it would be desirable to pursue Mylan's interest
in a possible development and commercialization agreement for other Penederm
products and authorized Mr. Malchow to convey the Penederm Board's position to
Mr. Jackson. To facilitate the selection of an investment banking firm prior to
the Penederm Board's next regularly scheduled meeting in April 1998, the
Penederm Board appointed a committee consisting of Mr. David Collins (Penederm's
Chairman), Dr. Harvey Sadow (another of Penederm's outside directors) and Mr.
Malchow (the "Investment Banker Selection Committee").

   Shortly following the February 25, 1998 meeting of the Penederm Board, Mr.
Malchow advised Mr. Jackson of the outcome of that meeting.

   On March 6, 1998, the Investment Banker Selection Committee met to interview
representatives of Lehman Brothers Inc. ("Lehman Brothers") and another
nationally recognized investment banking firm. Lehman Brothers and the other
firm were selected as candidates both because of their excellent reputations in
assisting public companies in evaluating strategic alternatives and because each
firm was widely recognized as expert in the pharmaceutical products and
healthcare industries. At the conclusion of the meeting, the Investment Banker
Selection Committee approved the engagement of Lehman Brothers and authorized
Mr. Malchow to execute an engagement agreement with Lehman Brothers on behalf of
Penederm on the basis of the terms proposed by Lehman Brothers at the meeting
(the "Lehman Brothers Engagement Agreement"). The Lehman Brothers Engagement
Agreement was executed on March 10, 1998 (see "--Opinion of Penederm's Financial
Advisor").

   Thereafter, for the next several weeks, Lehman Brothers examined Penederm's
business, financial condition, prospects and strategic alternatives with a view
to making a presentation to the Penederm Board at its regularly scheduled April
1998 meeting, and in connection with this examination, Lehman Brothers
representatives met with Penederm's senior management.

   On March 27, 1998, Penederm and Mylan entered into a confidentiality
agreement (the "Initial Confidentiality Agreement") to facilitate Penederm's
delivery of proprietary information to Mylan in connection with a possible
collaboration for product development and commercialization with respect to one
or more of three specified Penederm products. Thereafter, proprietary
information about these products was provided to Mylan. During discussions
between representatives of the two companies, the Mylan representatives
indicated heightened interest, on the basis of Mylan's review of this
information, in a possible acquisition of Penederm.

   At a regularly scheduled meeting of the Penederm Board held on April 23,
1998, Lehman Brothers made a presentation regarding its work in connection with
Penederm's evaluation of its strategic alternatives. A general discussion of
those matters ensued. It was the unanimous consensus of the Penederm Board that
it would not be in the best interests of Penederm Stockholders for Penederm to
initiate a process of actively soliciting possible buyers because such a process
would divert senior management's attention from Penederm's operations at a
crucial stage in Penederm's development, when the possibility of Penederm
generating operating profits in the near term appeared reasonably likely and
Penederm was critically dependent on the retention of its established research
and development staff and of its newly-hired sales force. However, the Penederm
Board unanimously concluded that there was some significant possibility, which
should be pursued, that Mylan--because of its existing familiarity with
Penederm's products and potential as well as its own stature in the
pharmaceutical products industry and its

                                       16
<PAGE>
 
repeatedly expressed view that Penederm represented a highly attractive
acquisition candidate that could advance Mylan's strategy of expanding into
dermatological products--might be in a position to formulate, very quickly, a
proposal at a purchase price that the Penederm Board would view as sufficiently
attractive to warrant negotiating a sale of Penederm to Mylan. The Penederm
Board also concluded that dialogue with Mylan, even if it did not result in an
acquisition of Penederm, could advance the possibility of Mylan and Penederm
entering into a product development and commercialization arrangement that could
be attractive to Penederm. The Penederm Board authorized Mr. Malchow, in
collaboration with Lehman Brothers and HEWM, to convey to Mylan the Penederm
Board's decision that Penederm was not for sale but would be willing to permit
Mylan expanded due diligence on Penederm for a 30-day period if Mylan was
willing to indicate immediately that it could realistically envision the
possibility of such due diligence enabling it to make an acquisition proposal at
a price exceeding $20 per share (on April 22, 1998, the day before the meeting,
the closing price of Penederm Common Stock on NASDAQ was $11-7/8).

   Within a few days of the April 23, 1998 meeting of the Penederm Board, the
position of the Penederm Board was conveyed to Mylan and its representatives.
Mylan's response, directly and through its financial advisor, Warburg Dillon
Read LLC ("Warburg Dillon Read"), was that it was willing to accept the offer of
expedited and expanded due diligence on the basis outlined by the Penederm
Board. A Supplement to the Confidentiality Agreement, dated May 6, 1998, was
thereafter executed in order to permit Mylan to receive proprietary information
about Penederm that was not limited to the three possible product collaborations
contemplated by the Initial Confidentiality Agreement.

   For the next four weeks, Mylan and Warburg Dillon Read carried out a due
diligence investigation regarding Penederm. In response to a request by Mylan
for an exclusivity agreement, Penederm representatives responded that such an
agreement would not be considered unless and until Mylan made a proposal to
Penederm that reflected a valuation of Penederm consistent with the Penederm
Board's views.

   On June 5, 1998, Warburg Dillon Read advised Lehman Brothers that Mylan was
prepared to move forward with a proposal in which Mylan would acquire Penederm
for $20 per share payable in Mylan Common Stock in a tax-free reorganization,
subject to additional due diligence, mutually acceptable agreements and certain
arrangements to enhance the prospects of the transaction being consummated
(including an option on unissued shares of Penederm Common Stock constituting
approximately 19.9% of the outstanding Penederm Common Stock, irrevocable
proxies from Penederm's directors and a cash fee in the event the transaction
was terminated because of the activities of another bidder).

   Also on June 5, 1998, Mr. Jackson wrote a letter to Mr. Malchow confirming
the discussion that had occurred earlier that day between Warburg Dillon Read
and Lehman Brothers. The letter indicated that Mylan's valuation remained
subject to mutual due diligence in order to verify the facts upon which it was
based. The letter listed several material matters upon which mutual agreement
would have to be reached. The letter proposed that the parties' respective due
diligence reviews be completed concurrently with the negotiation of the
transaction documents and indicated that drafts of the Merger Agreement, a stock
option agreement, the Voting Agreements and a reciprocal confidentiality
agreement (to facilitate Penederm performing due diligence on Mylan) were being
delivered that day.

   Later on June 5, 1998, the Penederm Board considered Mylan's proposal at a
special meeting. After receiving presentations from HEWM and Lehman Brothers,
and discussing the matter, the Penederm Board unanimously concluded that it was
willing to authorize Penederm to continue negotiations with Mylan only if Mylan
was willing to increase the per-share consideration to a level the Penederm
Board considered commensurate with Penederm's prospects and sufficient to
justify deviating from Penederm's own business plan. The Penederm Board directed
Lehman Brothers to convey this position to Warburg Dillon Read and to advise
Warburg Dillon Read that unless Mylan was willing to raise its valuation of
Penederm, the Penederm Board was not willing to authorize negotiation of
definitive agreements.

   On June 9, 1998, Warburg Dillon Read advised Lehman Brothers that Mylan was
now willing to exchange 0.68 of a share of Mylan Common Stock for each share of
Penederm Common Stock, which constituted a price of $21.12 per share of Penederm
Common Stock based on the closing price of Mylan Common Stock on the NYSE the

                                       17
<PAGE>
 
previous day (the closing price of Penederm Common Stock on NASDAQ that day had
been $14-3/4). Warburg Dillon Read also informed Lehman Brothers that this offer
represented Mylan's maximum and final offer and that Mylan had raised its price
as a final incentive to Penederm to move towards finalizing definitive
agreements immediately. At a special meeting of the Penederm Board held later
that day, the Penederm Board, after a presentation from Lehman Brothers and a
general discussion, unanimously authorized Mr. Malchow, with the assistance of
Lehman Brothers and HEWM, to conduct immediate negotiations with Mylan and its
representatives and perform the necessary related due diligence, with a view to
bringing back to the Penederm Board for its evaluation definitive agreements
based upon Mylan's increased offer.

   On June 11, 1998, at a meeting at Mylan's headquarters between Mr. Malchow
and representatives of Lehman Brothers, on the one hand, and Mr. Jackson, other
representatives of Mylan and Bertek, and Warburg Dillon Read, on the other hand,
a reciprocal confidentiality agreement was signed to facilitate Penederm's
receipt of proprietary information from Mylan, and Mylan provided proprietary
information to Penederm's representatives regarding its business, financial
condition and prospects.

   At the conclusion of this meeting the representatives of Penederm and Mylan
jointly concluded that it was in the respective best interests of both companies
to seek to complete the negotiations and submit definitive agreements to their
respective boards of directors as soon as possible. Recognizing, however, the
possibility that open issues might not necessarily be resolved immediately, and
in response to Mylan's request for a brief exclusivity period (which request
had, as indicated above, been declined at an earlier stage in the negotiations),
Penederm and Mylan entered into a letter agreement pursuant to which Penederm
agreed that, until July 10, 1998 or such earlier date as Penederm and Mylan
either executed definitive agreements or mutually agreed to discontinue
discussions of the proposed transaction, Penederm would not solicit any proposal
from, furnish any information to or participate in any negotiations with any
third party regarding any acquisition of Penederm or any material portion of its
stock or assets.

   During the week of June 15, 1998, Mylan completed its due diligence on
Penederm, Penederm completed its due diligence on Mylan, and intensive
negotiations continued between the two companies and their respective financial
and legal advisors.

   At a special meeting held on June 17, 1998, the Penederm Board received from
Mr. Malchow and Lehman Brothers a summary of the information that had been
provided by Mylan at the due diligence meeting on June 9, as well as an interim
report from Lehman Brothers and HEWM regarding the progress of negotiations on
the definitive agreements.

   On June 19, 1998, the Mylan Board received detailed presentations from its
senior management and Warburg Dillon Read regarding the status of the due
diligence and the negotiations. The Mylan Board also received a due diligence
report from its outside counsel, Buchanan Ingersoll Professional Corporation
("Buchanan Ingersoll"). The Mylan Board unanimously concluded that it was
willing to authorize its senior management to continue negotiations on the
definitive agreements.

   On June 21, 1998, the Penederm Board received detailed presentations from Mr.
Malchow, Lehman Brothers and HEWM regarding the proposed transaction, and Lehman
Brothers indicated that it was willing to render an opinion that, as of the date
the opinion was rendered, from a financial point of view the Exchange Ratio was
fair to Penederm Stockholders. After discussing the matter, the Penederm Board
unanimously directed Mr. Malchow, with the assistance of Lehman Brothers and
HEWM, to negotiate further on certain provisions of the various agreements. The
Penederm Board also unanimously authorized Mr. Malchow to pursue Mylan's recent
suggestion that, in conjunction with the execution of the definitive agreements,
the companies commit to completing negotiations on a co-promotion agreement for
Penederm's Avita(R) cream and gel products modeled on the Mentax(R) Co-Promotion
Agreement, but with certain royalty and licensing payments to be paid to
Penederm upon execution of the agreement (the "Avita(R) Co-Promotion
Agreement").

   Negotiations continued over the next two days. On June 23, 1998, the Mylan
Board received a report from Warburg Dillon Read and Buchanan Ingersoll as to
the progress of the negotiations and the tentative terms which had been
negotiated since June 19, 1998. Warburg Dillon Read indicated that it was
willing to render an opinion

                                       18
<PAGE>
 
that, as of June 23, 1998, from a financial point of view the Exchange Ratio was
fair to Mylan. The Mylan Board unanimously authorized the execution of
definitive agreements on the basis that had been negotiated.

   At a special meeting held later on June 23, 1998, the Penederm Board received
a presentation from Mr. Malchow, Lehman Brothers and HEWM regarding the outcome
of those negotiations. The Penederm Board also received Lehman Brothers' written
opinion that, as of that date, from a financial point of view the Exchange Ratio
was fair to Penederm Stockholders (see "--Opinion of Penederm's Financial
Advisor"). After discussion, the Penederm Board unanimously approved the Merger
Agreement, the Stock Option Agreement and the terms of the Avita(R) Co-Promotion
Agreement.

   Before the opening of trading on June 24, 1998, the Merger Agreement, the
Stock Option Agreement between Mylan and Penederm dated June 24, 1998 (as
amended and restated, the "Stock Option Agreement") and the Voting Agreements
were executed and publicly announced in a joint press release, which Mr. Malchow
read at the annual meeting of Penederm Stockholders held later that morning
(this meeting had previously been scheduled in a notice of meeting and proxy
statement dated May 11, 1998, preceding the negotiations between Penederm and
Mylan). The Avita(R) Co-Promotion Agreement was separately negotiated, and
executed and publicly announced on July 10, 1998.

Penederm's Reasons for the Merger; Recommendation of the Penederm Board

   On June 23, 1998, the Penederm Board unanimously determined the Merger to be
advisable and fair to, and in the best interests of, Penederm and the Penederm
Stockholders. The Penederm Board unanimously approved the Merger Agreement and
unanimously decided to recommend that Penederm Stockholders approve and adopt
the Merger Agreement. In making this decision, the Penederm Board considered the
factors listed below:

   1.  As indicated above (see "--Background of the Merger"), at its April 23,
1998 meeting the Penederm Board determined that initiating an active process of
soliciting possible buyers for Penederm would be detrimental to senior
management's ability to focus on the pursuit of Penederm's business plan at a
crucial stage in Penederm's development. In approving the Merger Agreement on
June 23, 1998, the Penederm Board also concluded that there was substantial
uncertainty as to the prospect that such a process would yield value for
Penederm Stockholders in excess of the Merger in light of the uncertainty that
would necessarily continue, for some substantial time into the future, to affect
Penederm's attractiveness as an acquisition candidate in light of (i) Penederm's
dependence on a limited number of products, several of which, while they could
prove key to Penederm's future profitability, were still in the development or
testing stage and may take years to reach the marketplace, and (ii) the presence
of competitors with substantially greater resources to devote to product
development, testing and marketing and with substantially more diversified lines
of products, many of which were already in the marketplace. The Penederm Board
determined that, but for Mylan's unsolicited overture to Penederm and its
willingness to acquire Penederm on the terms of the Merger Agreement, Penederm
would more likely enhance long-term value for Penederm Stockholders by
continuing to develop, test and market its line of products and to seek partners
(such as Mylan, in the case of the Mentax(R) Co-Promotion Agreement and the
Avita(R) Co-Promotion Agreement) with which to enter into product-specific
collaborative arrangements, and that the risks of deviating from this plan to
pursue possible buyers outweigh the potential and speculative benefits of that
process.

   2.  However, the Penederm Board determined that the Merger presented Penederm
Stockholders with a unique strategic opportunity to maximize the long-term value
of their investment in Penederm by exchanging their shares of Penederm Common
Stock for Mylan Common Stock, giving them the opportunity to continue to
participate in Penederm's potential growth while (i) substantially reducing the
risk that such growth will be impeded by Penederm's limited resources as an
independent entity; (ii) substantially reducing the risks associated with
transitioning from a product development-oriented company to a commercial sales
and marketing-oriented enterprise; and (iii) simultaneously offering them the
chance to benefit from Mylan's substantially greater capacity to develop, test
and market Penederm's products as part of Mylan's broader strategy of expanding
its range of products beyond seasoned generic drugs to innovative proprietary
pharmaceuticals. The Penederm Board also believes there are special
opportunities for synergistic benefits to be realized from a combination of
Penederm and Mylan, including (i) reduction in overhead relating to distribution
and manufacturing activities; (ii) efficiencies in the management of trade
relations and managed care contracting; (iii) expanded distribution of
Penederm's products

                                       19
<PAGE>
 
into new market segments such as hospitals and institutions; and (iv)
development and commercialization of new oral dermatological dosage forms,
although the Penederm Board also recognizes the risk that such benefits may not
be realized (see "RISK FACTORS--Uncertainties in Realizing Synergies of the
Merger").

   3.  In reaching this conclusion, the Penederm Board considered not only the
value of the consideration being offered to Penederm Stockholders in the Merger
(see paragraph 4 below), but also certain other specific aspects of Mylan's
proposal, including:

     (i) Mylan's existing familiarity with Penederm and its product line as a
         result of the discussions that started in early 1997 and led to the
         Mentax(R) Co-Promotion Agreement (see "--Background of the Merger");

     (ii) Mylan's repeatedly expressed interest, throughout that period, in
          broadening its relationship with Penederm through additional product
          collaborations (such as the Avita(R) Co-Promotion Agreement) and its
          demonstrated commitment to the acquisition of Penederm as an integral
          step in Mylan's own business strategy;

     (iii)Mylan's willingness to complete due diligence on Penederm in a short
          period and to increase substantially its offer for Penederm (from a
          price of up to $18 per share to an exchange ratio representing, on the
          date it was offered, approximately $21 per share);

     (iv) Mylan's willingness to reduce the risk that adverse developments in
          Penederm's business would give Mylan the right to terminate the Merger
          Agreement by agreeing to a stringent articulation, in the Merger
          Agreement, of the material adverse events that would trigger a
          termination right on Mylan's part (see "THE MERGER AGREEMENT AND THE
          RELATED AGREEMENTS--Conditions to the Merger");

     (v)  Mylan's intention to retain Penederm's own workforce to continue
          developing, testing and marketing Penederm's existing and potential
          products; and

     (vi) the vigorous nature of the arm's length negotiations that resulted in
          the final terms of the transaction.

   4.  The Penederm Board also took into account: (i) its own, Lehman Brothers'
and Mylan's respective assessments of Penederm's business, financial condition,
existing products, pipeline of potential products, contractual arrangements,
plans and prospects; (ii) its own, Lehman Brothers' and Mylan's respective
assessments of Mylan's business, financial condition, prospects and capacity, as
a major participant in the pharmaceutical products industry, to exploit
Penederm's potential; and (iii) the perception of Mylan's prospects on the part
of professional securities analysts who follow both Mylan and its competitors.

   5.  The Penederm Board viewed the Exchange Ratio as an attractive price
for Penederm. Among other factors, the Penederm Board took into consideration:

     (i)  The Penederm Board's evaluation of financial data presented in
          connection with Lehman Brothers' analysis (see "--Opinion of
          Penederm's Financial Advisor"). On the basis of this data, the
          Penederm Board concluded that the Exchange Ratio compared favorably to
          the per-share prices negotiated in recent comparable acquisitions in
          Penederm's industry and to any reasonable estimate of the near-term
          value of Penederm if it were to remain independent;

     (ii) The relationship of the Exchange Ratio to the historical market prices
          for Penederm Common Stock, including the fact that the Exchange Ratio
          represented (based on the closing prices of Penederm Common Stock and
          Mylan Common Stock, respectively, on the relevant dates) a premium of
          approximately 43.2% over the closing price of Penederm Common Stock on
          June 8, 1998 (the last day preceding Mylan's offer of the Exchange
          Ratio), approximately 36.5% over the closing price of Penederm Common
          Stock on June 19, 1998 (the last trading day preceding the meeting of
          the Penederm Board at which Lehman Brothers presented the financial
          analysis supporting its fairness

                                       20
<PAGE>
 
          opinion), approximately 39.0% over the closing price of Penederm
          Common Stock on June 23, 1998 (the last trading day preceding the
          meeting of the Penederm Board at which the Merger Agreement was
          approved), and approximately 77.6%, 88.5% and 84.1% over the average
          closing prices of Penederm Common Stock during the 90-day, 180-day and
          52-week periods, respectively, preceding the execution of the Merger
          Agreement (see paragraph 7 below);

     (iii)The trading history and pattern of Mylan Common Stock, which
          indicated to the Penederm Board that the shares of Mylan Common Stock
          that Penederm Stockholders would receive in the Merger (and that would
          represent approximately 4.8% of the shares of Mylan Common Stock
          outstanding immediately after the Effective Time) would be readily
          tradeable by those Penederm Stockholders who do not wish to make a
          long-term investment in Mylan and would therefore offer immediate
          liquidity to such Penederm Stockholders; and

     (iv) The facts that (i) the Merger is conditioned upon the receipt of
          opinions of counsel that it will be treated for federal income tax
          purposes as a reorganization within the meaning of Section 368 of the
          Code and, (ii) assuming such treatment, no gain or loss will be
          recognized by Penederm Stockholders upon their exchange of Penederm
          Common Stock for Mylan Common Stock (except with respect to any cash
          received in lieu of fractional shares).

   6.  The Penederm Board took into consideration Lehman Brothers' oral opinion
that, as of June 23, 1998 (the date the Merger Agreement was approved by the
Penederm Board), the Exchange Ratio was from a financial point of view fair to
Penederm Stockholders (see "--Opinion of Penederm's Financial Advisor"). A copy
of Lehman Brothers' confirmatory written opinion dated June 23, 1998, setting
forth the assumptions made, matters considered and review undertaken, is
attached to this Proxy Statement/Prospectus as Appendix D. The full text of such
written opinion is incorporated herein by reference, and the foregoing
description thereof is qualified in its entirety by such reference. Penederm
Stockholders are urged to read such opinion carefully in its entirety.

   7.  The Penederm Board took note of the fact that the Merger Agreement
provides for a fixed Exchange Ratio of 0.68 of a share of Mylan Common Stock for
each share of Penederm Common Stock, without any so-called "collar" provision,
floating exchange ratio or termination provision designed to ensure a minimum
value to Penederm Stockholders at the instant of the Effective Time. The
Penederm Board recognized that a fixed exchange ratio posed some risk to
Penederm Stockholders in the event of a decline in the value of Mylan Common
Stock (see "RISK FACTORS--Fixed Exchange Ratio Despite Possible Changes in Stock
Prices" and "--Federal Trade Commission Investigation" and "SUMMARY--Market
Price Information"), and that, if such a decline occurred, the Exchange Ratio
might represent less of a premium over the market price of Penederm Common Stock
than it represented on June 23, 1998, when the Penederm Board approved the
Merger Agreement. However, the Penederm Board concluded that, from a long-term
perspective as distinguished from the market price of Mylan Common Stock on any
given day, the Exchange Ratio represented an attractive price for Penederm, in
part, because it preserved for Penederm Stockholders the "upside" opportunity to
benefit from any future increase in the market price of Mylan Common Stock,
whether due to the combination of the two companies (see paragraph 2 above) or
otherwise. After discussing with Lehman Brothers the pharmaceutical products
industry generally and professional securities analysts' perceptions of Mylan
specifically, the Penederm Board determined that the benefits of a fixed
exchange ratio at least equalled and possibly outweighed the risks.

   8.  The Penederm Board considered generally the material terms of the Merger
and concluded that such terms were appropriate for a transaction of the nature
of the Merger. The Penederm Board recognized that the conditions to Mylan's
obligations to consummate the Merger include conditions beyond the ability of
Penederm to control (see "THE MERGER AGREEMENT AND THE RELATED AGREEMENTS--
Conditions to the Merger") and concluded that the risk of nonconsummation of the
Merger has been appropriately limited and is outweighed by the potential
advantages of the Merger to Penederm Stockholders.

   9.  The Penederm Board considered the termination provisions of the Merger
Agreement, including the obligation of Penederm to pay Mylan a termination fee
of $9 million under certain circumstances involving an acquisition of Penederm
by a competing bidder (see "THE MERGER AGREEMENT AND THE RELATED AGREEMENTS--
Termination Fee; Expenses of the Merger"), as well as the provisions of the
Stock Option

                                       21
<PAGE>
 
Agreement, under which Mylan has the right to buy, at $20 per share, newly
issued shares of Penederm Common Stock representing approximately 19.9% of the
presently outstanding shares under certain generally similar circumstances and
certain other circumstances involving a competing bid for Penederm (see "THE
MERGER AGREEMENT AND THE RELATED AGREEMENTS--The Stock Option Agreement"). The
Penederm Board noted that these provisions had been insisted upon by Mylan as a
condition to entering into the Merger Agreement in order to enhance the
likelihood that Mylan would achieve its objective of acquiring Penederm. The
Penederm Board recognized that these provisions would increase the cost to a
competing bidder of acquiring Penederm and might therefore deter competing bids.
However, in light of its decision that Penederm was not for sale (see paragraph
1 above), that the Merger represented a unique strategic opportunity for
Penederm Stockholders (see paragraph 2 above) and that, for a number of reasons,
Mylan was the most likely bidder able to satisfy itself promptly that Penederm's
value as an acquisition candidate was consistent with the Penederm Board's
view of the long-term value of Penederm (see paragraphs 1 and 3 above), the
Penederm Board decided that it was appropriate to accede to Mylan's
requirements, as they had been modified in the process of the vigorous
negotiation between the two companies.

   The foregoing discussion of the factors considered by the Penederm Board is
not intended to be exhaustive, but summarizes all material factors considered.
The Penederm Board did not assign any relative or specific weights to the
foregoing factors nor did it specifically characterize any factor as positive or
negative (except as described above), and individual directors may have given
differing weights to differing factors and may have viewed certain factors more
positively or negatively than others. Throughout its deliberations, the Penederm
Board received the advice of HEWM, its legal advisor, and Lehman Brothers, its
financial advisor.

   The Penederm Board unanimously recommends that Penederm Stockholders approve
the Merger Agreement and the transactions contemplated thereby, including the
Merger.

Opinion of Penederm's Financial Advisor

   Lehman Brothers has acted as financial advisor to Penederm in connection with
the Merger. As part of its role as financial advisor to Penederm, Lehman
Brothers rendered to the Penederm Board an opinion dated June 23, 1998 (the
"Lehman Brothers Opinion") as to the fairness, from a financial point of view,
to Penederm Stockholders of the Exchange Ratio to be offered to Penederm
Stockholders in the Merger.

   On June 21, 1998, in connection with an evaluation of the Merger by the
Penederm Board, Lehman Brothers made a presentation to the Penederm Board with
respect to the Merger. At that time, Lehman Brothers reviewed the information
and financial data described below with the Penederm Board, and advised the
Penederm Board that it was prepared to render its opinion that the proposed
Exchange Ratio to be offered to Penederm Stockholders in the Merger was fair
from a financial point of view, as of that date, to Penederm Stockholders (see
"--Background of the Merger"). At the June 23, 1998 meeting of the Penederm
Board, Lehman Brothers delivered its written opinion that the proposed Exchange
Ratio to be offered to Penederm Stockholders in the Merger was fair from a
financial point of view to such Penederm Stockholders as of the date of such
opinion. A copy of the Lehman Brothers Opinion, which sets forth assumptions
made and matters considered therein and limitations thereof, is attached as
Appendix D to this Proxy Statement/Prospectus and is incorporated by reference.
Penederm Stockholders should read the Lehman Brothers Opinion for a discussion
of such assumptions, matters and limitations. The summary of the Lehman Brothers
Opinion set forth in this Proxy Statement/Prospectus is qualified in its
entirety by reference to the full text of the Lehman Brothers Opinion. There is
no requirement in the Merger Agreement or otherwise that the Lehman Brothers
Opinion be updated to any date subsequent to June 23, 1998.

   No limitations were imposed by Penederm on the scope of Lehman Brothers'
investigation or the procedures to be followed by Lehman Brothers in rendering
the Lehman Brothers Opinion, except that Lehman Brothers was not authorized to,
and did not, solicit any indications of interest from any third party with
respect to the purchase of all or part of Penederm's business. Lehman Brothers
was not requested to and did not make any recommendation to the Penederm Board
as to the form or amount of the consideration to be offered to Penederm
Stockholders in the Merger, which was determined through arm's length
negotiations between the parties. In arriving at the Lehman Brothers Opinion,
Lehman Brothers did not ascribe a specific range of value to Penederm, but made
its determination as to the fairness from a financial point of view of the
Exchange Ratio to be offered to Penederm

                                       22
<PAGE>
 
Stockholders in the Merger on the basis of the financial and comparative
analyses described below. The Lehman Brothers Opinion is for the use and benefit
of the Penederm Board and was rendered to the Penederm Board in connection with
its consideration of the Merger. The Lehman Brothers Opinion is not intended to
be and does not constitute a recommendation to any Penederm Stockholders as to
how such Penederm Stockholders should vote with respect to the Merger. Lehman
Brothers was not requested to opine to, and the Lehman Brothers Opinion does not
address, Penederm's underlying business decision to proceed with, or the effect
of, the Merger.

   In arriving at the Lehman Brothers Opinion, Lehman Brothers reviewed and
analyzed: (i) the Merger Agreement and the specific terms of the Merger, (ii)
Penederm's 1997 Form 10-K and such other publicly available information
concerning Penederm and Mylan that Lehman Brothers believed to be relevant to
its analysis, (iii) financial and operating information with respect to the
business, operations, assets, financial condition and prospects of Penederm
furnished to Lehman Brothers by Penederm, (iv) financial and operating
information with respect to the business, operations, assets, financial
condition and prospects of Mylan furnished to Lehman Brothers by Mylan, (v) a
trading history of Penederm Common Stock from June 17, 1996 to June 17, 1998,
and a comparison of that trading history with those of other companies that
Lehman Brothers deemed relevant, (vi) a trading history of Mylan Common stock
from June 17, 1996 to June 17, 1998, and a comparison of that trading history
with those of other companies that Lehman Brothers deemed relevant, (vii) a
comparison of Penederm's historical financial results and financial condition as
of the date of the Lehman Brothers Opinion with those of other companies that
Lehman Brothers deemed relevant, (viii) a comparison of Mylan's historical
financial results and financial condition as of the date of the Lehman Brothers
Opinion with those of other companies that Lehman Brothers deemed relevant, (ix)
a comparison of the financial terms of the Merger with the financial terms of
certain other transactions that Lehman Brothers deemed relevant, and (x)
published estimates of third-party research analysts with respect to the future
financial performance of Mylan. In addition, Lehman Brothers had discussions
with the respective management of Penederm and Mylan concerning its businesses,
operations, assets, financial condition and prospects and the operating
synergies expected by such management to result from the Merger, and undertook
such other studies, analyses and investigations as Lehman Brothers deemed
appropriate.

   In arriving at the Lehman Brothers Opinion, Lehman Brothers assumed and
relied upon the accuracy and completeness of the financial and other information
used by it without assuming any responsibility for independent verification of
such information, and further relied upon the advice of the management of
Penederm and Mylan that they were not aware of any facts or circumstances that
would make such information inaccurate or misleading. With respect to the
financial projections of Penederm, upon advice of Penederm, Lehman Brothers
assumed that such projections were reasonably prepared on a basis reflecting the
best available estimates and judgments of the management of Penederm as to the
future financial performance of Penederm, and Lehman Brothers relied upon such
projections in arriving at the Lehman Brothers Opinion. With respect to the
future financial performance of Mylan, upon advice of Mylan, Lehman Brothers
assumed that the published estimates of third-party research analysts were a
reasonable basis upon which to evaluate the future financial performance of
Mylan. In arriving at the Lehman Brothers Opinion, Lehman Brothers did not
conduct a physical inspection of the properties and facilities of Penederm or
Mylan, and did not make or obtain any evaluations or appraisals of the assets or
liabilities of Penederm. In addition, Penederm did not authorize Lehman Brothers
to solicit, and Lehman Brothers did not solicit, any indications of interest
from any third party with respect to the purchase of all or a part of the
business of Penederm. In addition, Lehman Brothers assumed that, as contemplated
by the Merger Agreement, the Merger will qualify as a reorganization within the
                       -                                                       
meaning of Section 368(a) of the Code, and therefore as a tax-free transaction
to Penederm Stockholders. The Lehman Brothers Opinion was necessarily based upon
market, economic and other conditions as they existed on, and could be evaluated
as of, the date of the Lehman Brothers Opinion.

   In connection with the preparation and delivery of the Lehman Brothers
Opinion to the Penederm Board, Lehman Brothers performed a variety of financial
and comparative analyses, as described below. The preparation of a fairness
opinion involves various determinations as to the most appropriate and relevant
methods of financial and comparative analysis and the application of those
methods to the particular circumstances, and therefore, such an opinion is not
readily susceptible to summary description. Furthermore, in arriving at the
Lehman Brothers Opinion, Lehman Brothers did not attribute any particular weight
to any analysis or factor considered by it, but rather made qualitative
judgments as to the significance and relevancy of each analysis and factor.
Accordingly, Lehman Brothers believes that its analyses must be considered as a
whole and that considering any portion of such analyses

                                       23
<PAGE>
 
and factors, without considering all analyses and factors, could create an
incomplete or misleading view of the process underlying the Lehman Brothers
Opinion. In its analyses, Lehman Brothers made numerous assumptions with respect
to industry performance, general business and economic conditions and other
matters, many of which are beyond Penederm's and Mylan's control. Any estimates
contained in these analyses are not necessarily indicative of actual values or
predictive of future results or values, which may be significantly more or less
favorable than as set forth therein. Additionally, analyses relating to the
value of businesses do not purport to be appraisals or to reflect the prices at
which businesses actually may be sold.

   Transaction Terms. Lehman Brothers considered that the implied value to be
received by Penederm Stockholders in the Merger, based upon the Exchange Ratio
and the closing price of Mylan Common Stock of $31.19 on June 17, 1998, was
$21.21 per share of Penederm Common Stock.

   Historical Stock Price Performance of Penederm and of Mylan. Lehman Brothers
reviewed the price performance of Penederm Common Stock for the twenty-four-
month period preceding the delivery of the Lehman Brothers Opinion and noted
that the closing price of Penederm Common Stock had fluctuated over that period
from a high of $17.50 to a low of $5.50, and was trading at $15.69 on June 17,
1998. Lehman Brothers also compared the price performance of Penederm Common
Stock to a weighted average of the stock prices of certain publicly traded drug
delivery companies and to the S&P 400 Index for the twenty-four-month period
prior to the delivery of the Lehman Brothers Opinion. The companies that Lehman
Brothers considered included Anesta Corp., Aradigm Corporation, Atrix
Laboratories, Inc., Cygnus, Inc., Emisphere Technologies, Inc., Fuisz
Technologies, Inc., Inhale Therapeutic Systems, InSite Vision Incorporated,
Medicis Pharmaceutical Corporation, Noven Pharmaceuticals, Inc. and Theratech,
Inc. (the "Comparable Drug Delivery Companies"). Lehman Brothers noted that the
price of Penederm Common Stock had declined 12.4% compared to an increase of
25.4% for the Comparable Drug Delivery Companies and an increase of 57.9% in the
S&P 400 Index over the past twenty-four months. Lehman Brothers also compared
the price performance of Mylan Common Stock to a weighted average of the stock
prices of certain publicly traded generic pharmaceutical companies and to the
S&P 400 Index for the twenty-four-month period prior to the delivery of the
Lehman Brothers Opinion (from June 17, 1996 to June 17, 1998). The companies
that Lehman Brothers considered included Alpharma Inc., Barr Laboratories, Inc.,
IVAX Corporation, Schein Pharmaceutical, Inc., Teva Pharmaceutical Industries
Ltd. and Watson Pharmaceuticals, Inc. (the "Comparable Generic Pharmaceutical
Companies"). Lehman Brothers noted that the price of Mylan Common Stock had
increased 55.7% compared to an increase of 24.3% for the Comparable Generic
Pharmaceutical Companies and an increase of 59.9% in the S&P 400 Index over the
past twenty-four months.

   Comparable Public Company Analysis of Penederm and of Mylan. Lehman Brothers
compared the historical, financial and operating performance of the Comparable
Drug Delivery Companies with the historical financial and operating performance
of Penederm and of the Comparable Generic Pharmaceutical Companies with that of
Mylan, based upon information that was publicly available at that time and based
upon information provided to Lehman Brothers by the respective management of
Penederm and Mylan. Lehman Brothers examined both the market value of the total
outstanding common equity ("Market Value") and the Market Value plus Debt minus
Cash ("Technology Value" or "Firm Value") of such comparable companies on a
primary and fully diluted basis. "Debt" equals long- and short-term debt and
current portion of long-term debt and capital lease obligations. "Cash" equals
cash and cash equivalents plus marketable securities. For Penederm, Lehman
Brothers noted that, at the proposed Exchange Ratio of 0.68 of a share of Mylan
Common Stock per share of Penederm Common Stock, the Market Value for Penederm
of $196.6 million was within the range of $52.2 million to $723.1 million, and
was below the mean of $236.6 million and above the median of $164.7 million, for
the Comparable Drug Delivery Companies. Lehman Brothers also noted that, at the
proposed Exchange Ratio of 0.68 of a share of Mylan Common Stock per share of
Penederm Common Stock, the Technology Value for Penederm of $194 million was
within the range of $45.5 million to $490.3 million, and was below the mean of
$200.3 million and above the median of $155.2 million, for the Comparable Drug
Delivery Companies.

   Lehman Brothers also noted that the mean and median price earnings ratios
using calendar 1998 estimates provided by First Call of the Comparable Drug
Delivery Companies were 23.1x and 23.1x, respectively, compared to 75.7x for
Penederm at the Exchange Ratio. The mean and median price earnings ratios using
calendar 1999

                                       24
<PAGE>
 
estimates provided by First Call of the Comparable Drug Delivery Companies were
16.1x and 16.5x, respectively, compared to 22.3x for Penederm at the Exchange
Ratio.

   Lehman Brothers noted that the Market Value for Mylan of $3.8 billion was
within the range of $520.3 million to $4.3 billion, and higher than the mean and
median of $1.7 billion and $1.1 billion, respectively, for the Comparable
Generic Pharmaceutical Companies. Lehman Brothers also noted that the Firm Value
for Mylan of $3.7 billion was within the range of $0.8 billion to $4.3, and was
higher than the mean and median of $1.8 billion and $1.2 billion, respectively,
for the Comparable Generic Pharmaceutical Companies.

   Lehman Brothers also noted that the mean and median price earnings ratios
using calendar 1998 estimates provided by First Call of the Comparable Generic
Pharmaceutical Companies were 25.9x and 23.1x, respectively, compared to 28.1x
for Mylan. The mean and median price earnings ratios using calendar 1999
estimates provided by First Call of the Comparable Generic Pharmaceutical
Companies were 20.0x and 18.1x, respectively, compared to 24.8x for Mylan.
Lehman Brothers further noted that the mean and median price earnings ratios
using calendar 1998 estimates provided by First Call divided by each company's
respective 5-year median growth rate as reported by the Institutional Brokers
Estimate System ("IBES") of the Comparable Generic Pharmaceutical Companies were
0.94x and 0.79x, respectively, compared to 1.40x for Mylan. The mean and median
price earnings ratios using calendar 1999 estimates provided by First Call
divided by each company's respective 5-year median growth rate as reported by
IBES of the Comparable Generic Pharmaceutical Companies were 0.73x and 0.61x,
respectively, compared to 1.24x for Mylan.

   However, because of the inherent differences between the businesses,
operations and prospects of Penederm and Mylan and the businesses, operations,
technology and prospects of the Comparable Drug Delivery Companies and
Comparable Generic Pharmaceutical Companies, as the case may be, Lehman Brothers
did not rely solely on the quantitative results of the analysis, but rather also
made qualitative judgments concerning differences between the financial and
operating characteristics and prospects of Penederm and Mylan and the Comparable
Drug Delivery Companies and Comparable Generic Pharmaceutical Companies, as the
case may be, that would affect the public trading values of each.

   Discounted Cash Flow Analysis for Penederm. Lehman Brothers performed a
discounted cash flow analysis based upon Penederm's projected financial
performance. This analysis was based upon information and projections provided
by Penederm's management. Lehman Brothers discounted to present value the
projected stream of after-tax cash flows and the terminal year value ("Terminal
Value") of the business. Terminal Value was based upon different ranges of
multiples of projected fiscal 2006 earnings before interest and taxes and
discount rates from 25% to 35%, which were chosen based on several assumptions
regarding factors such as the inflation rate, interest rates, the inherent
business risk in Penederm's operations as well as in the drug delivery industry
as a whole and the cost of capital to Penederm. The imputed value per share of
Penederm Common Stock resulting from these analyses ranged from $11.89 to
$23.91.

   Comparable Transaction Analysis for Penederm. Lehman Brothers compared the
financial terms of certain recent stock-for-stock merger transactions which
Lehman Brothers considered relevant with the financial terms of the Merger,
based upon information that was publicly available at the time and based upon
information provided to Lehman Brothers by Penederm management. The transactions
that Lehman Brothers considered comparable to the Merger included 35 stock-for-
stock merger transactions that occurred in the biopharmaceuticals industry since
1988 ("Comparable Transactions"). Lehman Brothers calculated the transaction
value per share implied by the exchange ratio for shares purchased directly from
the target company in the Comparable Transactions ("Merger Purchase Price Per
Share"). The mean, median, high and low Merger Purchase Price Per Share for the
Comparable Transactions was then compared to the target's stock price one day
and one month prior to the announcement of the transaction and to the target's
latest twelve-month high and low stock price to calculate the premium over such
prices ("Premium"). The mean, median, high and low Premiums one day prior to the
transaction announcement were 23.7%, 10.9%, 126.3% and (17.9%), respectively, in
the Comparable Transactions. Lehman Brothers noted that the Exchange Ratio
represented a 39.0% Premium over the price of Penederm Common Stock one day
prior to the announcement of the Merger (the closing price of Penederm Common
Stock on June 23, 1998 was $15.75) and was within the range of the Comparable
Transactions and above the mean and median of the Comparable Transactions. The
mean, median, high and low Premiums one month prior to the Merger


                                       25
<PAGE>
 
announcement were 29.4%, 23.4%, 220.0% and (31.5%), respectively, in the
Comparable Transactions. Lehman Brothers noted that the Exchange Ratio
represented a 61.7% Premium over the price of Penederm Common Stock of $13.54
one month prior to the announcement of the Merger and was within the range of
the Comparable Transactions and above the mean and median of the Comparable
Transactions.

   However, because the reasons for and the circumstances surrounding each of
the transactions analyzed were specific to each transaction and because of the
inherent differences between the business, operations, technology and prospects
of Penederm and the businesses, operations, technology and prospects of the
selected acquired companies analyzed, Lehman Brothers did not rely solely on the
quantitative results of the analysis but, rather, also made qualitative
judgments concerning differences between the characteristics of these
transactions and the Merger that would affect the acquisition values of Penederm
and such acquired companies.

   Exchange Ratio Analysis. Lehman Brothers compared the exchange ratios implied
by average historical prices of Penederm Common Stock and Mylan Common Stock to
the Exchange Ratio. Lehman Brothers reviewed the ratios of the closing stock
prices of Penederm Common Stock and Mylan Common Stock over various time periods
during the twenty-four-month period ended June 17, 1998 and computed the
premiums represented by the Exchange Ratio over the averages of these daily
ratios over various periods. The averages of these daily ratios of the closing
prices of Penederm Common Stock and Mylan Common Stock were 0.48 for the
previous 10 calendar days, 0.44 for the previous 30 calendar days, 0.43 for the
previous 60 calendar days, 0.45 for the previous 90 calendar days, 0.49 for the
previous 180 calendar days and 0.54 for the previous 52 weeks ending June 17,
1998. Lehman Brothers noted that the Exchange Ratio exceeded the high end of
these historical exchange ratios. The Exchange Ratio represented premiums of
42.5%, 55.0%, 58.8%, 49.5%, 38.7% and 26.9%, respectively, over the
aforementioned average exchange ratios of Penederm's and Mylan's stock prices.

   Relative Contribution Analysis. Lehman Brothers analyzed the pro forma
historical and projected financial contribution of Penederm and Mylan to the
combined company assuming consummation of the Merger based upon projections for
Penederm provided by Penederm and published estimates of research analysts for
Mylan. This analysis showed, among other things, that Penederm would contribute
4.6% of projected revenue and 2.8% of the projected operating income of the
combined company for the fiscal year ended March 31, 1999. Lehman Brothers noted
that Penederm Stockholders would own 4.8% of the combined company's common
stock.

   Mylan Common Stock Trading Volume Analysis. Lehman Brothers analyzed the
historical daily trading volume of Mylan Common Stock over various periods. The
10-, 30-, 60-, 90- and 120-day average daily trading volume of Mylan Common
Stock was approximately 642,460, 843,732, 931,688, 908,900 and 863,759 shares,
respectively.

   Pro Forma Analysis. Lehman Brothers analyzed the pro forma effects of the
Merger using Penederm's financial projections and publicly available financial
information for Mylan. Lehman Brothers noted that, at the Exchange Ratio,
assuming no synergy savings and excluding one-time extraordinary charges, the
Merger would be slightly dilutive to Mylan in fiscal years 1999 and 2000.
However, assuming moderate synergy savings, expected by Mylan and Penederm, the
Merger would be neither dilutive nor accretive in 1999 and accretive in 2000.

   Mylan Dividend Analysis. Lehman Brothers reviewed Mylan's dividend history
and indicated that Mylan had declared a quarterly dividend of $0.04 per share on
June 12, 1998. The quarterly dividend of $0.04 per share represented a 15.4%
payout ratio and an annualized dividend yield (assuming a $0.16 annual dividend)
of 0.52% based on the 30-day average trading price of Mylan Common Stock of
$30.89. Lehman Brothers also noted that Penederm does not pay dividends on
Penederm Common Stock and that, based on the Exchange Ratio, Penederm
Stockholders will receive through the Merger an annual $0.11 dividend for each
Penederm share owned.

   Lehman Brothers is an internationally recognized investment banking firm and
in connection with its investment banking activities is regularly engaged in the
evaluation of businesses and their securities in connection with mergers and
acquisitions, negotiated underwritings, competitive bids, secondary
distributions of listed and unlisted securities and private placements, and in
valuations for corporate and other purposes. The Penederm Board selected Lehman
Brothers because of Lehman Brothers' expertise, reputation and familiarity with
biopharmaceutical

                                       26
<PAGE>
 
and generic pharmaceutical companies and because its investment banking
professionals have substantial experience in transactions similar to the Merger.

   As compensation for its services in connection with the Merger under the
Lehman Brothers Engagement Agreement, Penederm has paid Lehman Brothers a
retainer fee of $100,000 upon its engagement and agreed to pay Lehman Brothers a
fee of $300,000 upon delivery of the Lehman Brothers Opinion. In addition,
Penederm has agreed to pay Lehman Brothers a fee of 1.25% of the Merger
Consideration (or approximately $2.6 million) contingent upon the consummation
of the Merger, against which the retainer fee and the opinion fee will be
credited. Penederm has also agreed to reimburse Lehman Brothers for its
reasonable out-of-pocket expenses and has agreed to indemnify Lehman Brothers
against certain liabilities that may arise in connection with its engagement. In
the ordinary course of its business, Lehman Brothers may trade in the securities
of Penederm and Mylan for its own account and for accounts of customers and,
accordingly, may at any time hold a short position in such securities.

Mylan's Reasons for the Merger

   The Board of Directors of Mylan believes that the acquisition of Penederm is
fair to and in the best interests of Mylan and its shareholders. In reaching
such determination, the Board of Directors of Mylan considered the following
material factors:

   (i)  Mylan's review of Penederm, including its business, operations,
        management, earnings and financial condition on an historical and
        prospective basis;

   (ii) the presentations by Warburg Dillon Read to the Board of Directors of
        Mylan on June 19, 1998 and June 23, 1998 and the written opinion
        rendered by Warburg Dillon Read, dated June 23, 1998, to the effect
        that, as of such date, the Exchange Ratio was fair to Mylan from a
        financial point of view;

  (iii) the terms and conditions of the Merger Agreement, including, without
        limitation, provisions relating to the number of shares of Mylan Common
        Stock to be issued in the Merger and the conditions to the consummation
        of the Merger;

   (iv) its belief that the Merger will significantly enhance its ability to
        serve physicians in both the primary care and dermatology markets;

    (v) the potential to leverage Penederm's current research and development
        efforts to assist current Mylan research and development efforts that
        have the potential to be improved by Penederm's potential drug-delivery
        technology; and

   (vi) its belief that the Merger would constitute an additional step towards
        Mylan's strategic goal of establishing proprietary pharmaceutical
        products.

   After reviewing the factors described above in their totality, the Mylan
Board determined that the Merger is in the best interests of Mylan and its
shareholders. In view of the variety of factors considered in connection with
its evaluation of the Merger, the Mylan Board found it impractical to, and did
not, quantify or attempt to assign relative weight to the specific factors
considered in reaching its determination. There can be no assurances that the
expected benefits of the Merger will be realized. See "RISK FACTORS."

Regulatory Approvals

   Under the HSR Act and the rules promulgated thereunder by the FTC, the Merger
may not be consummated until notifications have been given and certain
information has been furnished to the FTC and the Antitrust Division and
specified waiting period requirements have been satisfied. Mylan and Penederm
each filed notification and report forms under the HSR Act with the FTC and the
Antitrust Division on July 21, 1998. The FTC and the Antitrust Division granted
early termination of the waiting period on July 31, 1998. At any time before or
after consummation of the Merger, the Antitrust Division or the FTC could take
such action under the antitrust laws as it deems necessary or desirable in the
public interest, including seeking to enjoin the consummation of the Merger or
seeking divestiture of substantial assets of Mylan or Penederm. At any time
before or after the Effective Time, and

                                       27
<PAGE>
 
notwithstanding that the HSR Act waiting period has been terminated, any state
could take such action under its antitrust laws as it deems necessary or
desirable in the public interest. Such action could include seeking to enjoin
the consummation of the Merger or seeking divestiture of Penederm or businesses
of Mylan or Penederm. Private parties may also seek to take legal action under
antitrust laws under certain circumstances.

   Based on information available to them, Mylan and Penederm believe that the
Merger can be effected in compliance with federal and state antitrust laws.
However, there can be no assurance that a challenge to the consummation of the
Merger on antitrust grounds will not be made or that, if such a challenge were
made, Mylan and Penederm would prevail or would not be required to accept
certain conditions, possibly including certain divestitures, in order to
consummate the Merger.

   Consummation of the Merger is conditioned upon the receipt of all material
governmental authorizations, consents, orders and approvals, subject to waiver
of such conditions, in accordance with the terms of the Merger Agreement.
Although Mylan and Penederm have agreed to use commercially reasonable efforts
to secure all such approvals, there can be no assurance regarding the timing of
such approvals or that such approvals will, in fact, be obtained.

Interests of Certain Persons in the Merger

   In considering the approval by the Penederm Board of the Merger, Penederm
Stockholders should be aware that the members of the Penederm Board and
management of Penederm have certain interests in, and will receive benefits
from, the Merger that are in addition to, and differ from, the interests of and
benefits to Penederm stockholders generally. No director or executive officer of
Penederm had or is expected to have a business relationship with Mylan prior to
the Effective Time.

   Penederm's directors and executive officers have previously been granted
options to purchase Penederm Common Stock. Such options will be assumed by Mylan
at the Effective Time (see "THE MERGER AGREEMENT AND THE RELATED AGREEMENTS--
Treatment of Options"). As of the Record Date, directors and executive officers
of Penederm held options to purchase an aggregate of 900,069 shares of Penederm
Common Stock, including options to purchase an aggregate of 242,500 shares of
Penederm Common Stock held by non-employee directors. Such options are
exercisable at exercise prices ranging from $.55 to $20.50 per share. Pursuant
to a resolution of the Penederm Board adopted in December 1997, all Penederm
stock options, including those held by Penederm executive officers and
directors, will become fully vested immediately upon the consummation of the
Merger.

   In addition, Mylan has consented to (and the Penederm Board intends to
consider) Penederm entering into arrangements with each of Messrs. Lloyd H.
Malchow (Penederm's President and Chief Executive Officer) and Michael A. Bates
(Penederm's Chief Financial Officer) providing for (i) the payment to each of
them, if their employment terminates following the Effective Time, of an amount
equal to the maximum bonus each could have earned under Penederm's existing
bonus guidelines for 1998 if he had remained in his present position through
year-end, and (ii) the payment of six months' salary as severance from Penederm.
Messrs. Malchow and Bates are in discussions with Mylan with respect to the
role, if any, they will play in the combined company after the Effective Time.

   The Merger Agreement provides that for six years after the Effective Time,
Mylan shall cause the Surviving Corporation, and shall guarantee the obligations
of the Surviving Corporation, to (a) maintain in effect the current provisions
regarding indemnification of officers and directors contained in the charter and
bylaws of Penederm and in any indemnification agreements of Penederm and (b)
indemnify the past and present officers and directors of Penederm to the fullest
extent to which Penederm is permitted to indemnify such officers and directors
under its charter, bylaws and applicable law. Further, Mylan shall or shall
cause the Surviving Corporation to provide, for a period of six years from the
Effective Time, the current directors and officers of Penederm an insurance and
indemnification policy that provides coverage for events prior to the Effective
Time that is substantially similar to the policy currently maintained by
Penederm; provided that Mylan or the Surviving Corporation, as applicable, shall
not be required to spend as an annual premium for such insurance an amount in
excess of 200% of the annual premium paid for such insurance in effect prior to
the date of the Merger Agreement.

                                       28
<PAGE>
 
   The Penederm Board was aware of these interests and considered them, among
other matters, in approving the Merger Agreement and the transactions
contemplated thereby.

Accounting Treatment

   The Merger will be accounted for by Mylan under the purchase method of
accounting in accordance with GAAP. Under the purchase method of accounting, all
of the assets and liabilities of Penederm will be recorded in Mylan's
consolidated financial statements at their estimated fair values at the
Effective Time, and the consideration to be paid in the Merger will be allocated
to such assets and liabilities based on such fair values. The amount by which
such consideration exceeds the fair value of the net assets acquired by Mylan
through the Merger will be recorded as goodwill. Mylan's consolidated financial
statements will include the operations of Penederm after the Effective Time.
Income (or loss) of Penederm prior to the Effective Time will not be included in
the income of the combined company.

   The selected unaudited pro forma combined financial data and the unaudited
pro forma combined financial statements contained in this Proxy
Statement/Prospectus have been prepared using the purchase accounting method to
account for the Merger. See "SUMMARY--Selected Unaudited Pro Forma Combined
Financial Data."

Certain Federal Income Tax Consequences

   The following discussion summarizes the material federal income tax
considerations generally applicable to Penederm Stockholders. It is a condition
to the obligation of Mylan to consummate the Merger that Mylan shall have
received an opinion of Buchanan Ingersoll, in form and substance reasonably
satisfactory to Mylan, and it is a condition to the obligation of Penederm to
consummate the Merger that Penederm shall have received an opinion of HEWM, in
form and substance reasonably satisfactory to Penederm, in each case dated as of
the date upon which the Merger is consummated (the "Effective Date") and based
on representations contained in the Merger Agreement, to the effect that the
Merger will constitute a "reorganization" within the meaning of Section 368(a)
of the Code and that Penederm, Mylan and Merger Sub will each be a party to that
reorganization within the meaning of Section 368(b) of the Code. The discussion
below under "--Exchange of Penederm Common Stock for Mylan Common Stock," "--
Cash Received in Lieu of Fractional Shares" and "--Reporting Requirements"
assumes that the Merger will be treated in accordance with the opinions of
Buchanan Ingersoll and HEWM described in the preceding sentence. There can be no
assurance that the Internal Revenue Service (the "IRS") will not take a contrary
view, and no ruling from the IRS has been or will be sought.

   The discussion below is based upon the Code, the applicable Treasury
Department regulations thereunder, judicial authority and current administrative
rulings and practice, all as in effect as of the date hereof. Future
legislative, judicial or administrative changes or interpretations could alter
or modify the statements and conclusions set forth herein, and any such changes
or interpretations could have retroactive effect and could affect the federal
income tax consequences to Penederm Stockholders.

   The following discussion does not address the consequences of the Merger
under state, local or foreign law, nor does the discussion address all aspects
of federal income taxation that may be important to a Penederm Stockholder in
light of such stockholder's particular circumstances or tax issues which may be
significant to Penederm Stockholders subject to special rules, including,
without limitation, financial institutions, insurance companies, foreign
individuals and entities, tax-exempt entities, dealers in securities, persons
who acquired Penederm Common Stock pursuant to the exercise of an employee
option (or otherwise as compensation) or persons holding Penederm Common Stock
as part of an integrated investment (including a "straddle") composed of
Penederm Common Stock and one or more other positions. This discussion assumes
that Penederm Stockholders hold their respective Penederm Common Stock as
capital assets within the meaning of Section 1221 of the Code.

   Exchange of Penederm Common Stock for Mylan Common Stock. Except as discussed
   below under "--Cash Received in Lieu of Fractional Shares," no gain or loss
   will be recognized for federal income tax purposes by Penederm Stockholders
   who exchange their Penederm Common Stock for Mylan Common Stock pursuant to
   the Merger. The aggregate tax basis of Mylan Common Stock received as a
   result of the Merger will be the same as the stockholder's aggregate tax
   basis in the Penederm Common Stock surrendered in the exchange

                                       29
<PAGE>
 
   (reduced by any tax basis allocable to fractional shares exchanged for cash),
   and the holding period of the Mylan Common Stock received will include the
   holding period of the Penederm Common Stock surrendered therefor.

   Cash Received in Lieu of Fractional Shares. The payment of cash to a Penederm
   Stockholder in lieu of a fractional share interest in Mylan Common Stock will
   be treated as if the fractional share had been distributed as part of the
   exchange and then redeemed by Mylan. The cash payment will be treated as
   having been received as a distribution in payment for the Mylan Common Stock
   hypothetically redeemed as provided in Section 302 of the Code and generally
   should result in the recognition of capital gain or loss measured by the
   difference between the amount of cash received and the portion of the tax
   basis of the Penederm Common Stock allocable to such fractional share
   interest. In the case of an individual, capital gain recognized with respect
   to cash received in lieu of fractional share interests in Mylan Common Stock
   generally will be subject to United States federal income tax at a maximum
   rate of 20% if such individual held his or her Penederm Common Stock for more
   than one year at the Effective Time and at ordinary income rates as a short-
   term capital gain if such individual held his or her Penederm Common Stock
   for one year or less at the Effective Time. The deductibility of capital
   losses is subject to limitation.

   Reporting Requirements. Each Penederm Stockholder that receives Mylan Common
   Stock in the Merger will be required to file with such holder's federal
   income tax return a statement setting forth the basis of the Penederm Common
   Stock surrendered and the fair market value of the Mylan Common Stock and any
   other property received in the Merger, and to retain permanent records of
   these facts relating to the Merger.

   Backup Withholding. Unless an exemption applies under applicable law and
   regulations, the Exchange Agent (as defined in "THE MERGER AGREEMENT AND THE
   RELATED AGREEMENTS--Exchange of Shares") is required to withhold, and will
   withhold, 31% of any cash payments to a Penederm Stockholder in the Merger
   unless the stockholder provides the appropriate form as described below. Each
   Penederm Stockholder should complete and sign the Substitute Form W-9
   included as part of the letter of transmittal to be sent to each Penederm
   Stockholder, so as to provide the information (including such stockholder's
   taxpayer identification number) and certification necessary to avoid backup
   withholding, unless an applicable exemption exists and is proved in a manner
   satisfactory to Mylan and the Exchange Agent.

   The preceding discussion does not purport to be a complete analysis or
   discussion of all potential tax effects relevant to the Merger. Thus,
   Penederm Stockholders are urged to consult their own tax advisors as to the
   specific tax consequences to them of the Merger, including tax return
   reporting requirements, the applicability and effect of federal, state, local
   and other applicable tax laws and the effect of any proposed changes in the
   tax laws.

Absence of Appraisal Rights

   Penederm is incorporated under Delaware law, and the DGCL governs the
availability of appraisal rights with respect to mergers involving Penederm.
Penederm Stockholders are not entitled to appraisal rights under the DGCL in
connection with the Merger Agreement and the consummation of the transactions
contemplated thereby.

                 THE MERGER AGREEMENT AND THE RELATED AGREEMENTS

   This Proxy Statement/Prospectus contains a brief summary of certain
provisions of the Merger Agreement, the Stock Option Agreement and the Voting
Agreements. This summary is qualified in its entirety by reference to the full
texts of such agreements, which are included as Appendices A, B and C hereto and
which are incorporated herein by reference.

General

   Pursuant to the Merger Agreement, Merger Sub will be merged with and into
Penederm and Penederm will become a wholly-owned subsidiary of Mylan. At the
Effective Time, each outstanding share of Penederm Common

                                       30
<PAGE>
 
Stock will be converted into the right to receive 0.68 of a share of Mylan
Common Stock (or cash in lieu of fractional shares) as described herein. The
name of the Surviving Corporation shall be "Penederm Incorporated."

Consideration to Be Received in the Merger

   At the Effective Time, each share of Penederm Common Stock issued and
outstanding immediately prior to the Effective Time will, by virtue of the
Merger and without any action on the part of the holder thereof, be converted
into the right to receive 0.68 of a share of Mylan Common Stock.

   No fractional shares of Mylan Common Stock will be issued in the Merger. Each
holder of Penederm Common Stock who upon surrender of certificates representing
such Penederm Common Stock (each, a "Certificate") therefor would be entitled to
receive a fraction of a share of Mylan Common Stock will receive, in lieu of
such fractional share, cash in an amount equal to such fraction multiplied by
the closing price of Mylan Common Stock on the Effective Date, less the amount
of any taxes which may be required to be withheld under any provision of
federal, state, local or foreign tax law.

   Each share of Penederm Common Stock issued and held in Penederm's treasury at
the Effective Time shall, by virtue of the Merger, cease to be outstanding and
shall be cancelled and retired without payment of any consideration thereof.

Exchange of Shares

   As soon as practicable after the Effective Time, Mylan will instruct American
Stock Transfer and Trust Company (the "Exchange Agent") to send to each Penederm
Stockholder of record a letter of transmittal for use in the exchange of
Penederm Common Stock. As soon as practicable after the Effective Time, Mylan
will deposit with the Exchange Agent the aggregate consideration for the Merger
to be paid in respect of the Penederm Common Stock to the holders thereof.

   Upon surrender to the Exchange Agent of a Certificate or Certificates,
together with a properly completed letter of transmittal, the holder of such
Certificate shall be entitled to receive in exchange therefor that number of
Mylan Common Stock which such holder has the right to receive (and any amount of
cash payable in lieu of fractional shares), after giving effect to any required
withholding tax.

   If any portion of the Merger Consideration is to be paid to a person other
than the registered holder of Penederm Common Stock formerly represented by the
Certificate or Certificates surrendered in exchange for the Merger
Consideration, it shall be a condition to such payment that the Certificate or
Certificates so surrendered shall be properly endorsed or otherwise be in proper
form for transfer and that the person requesting such payment shall pay to the
Exchange Agent any transfer or other taxes required as a result of such payment
to a person other than the registered holder of such Penederm Common Stock or
establish to the satisfaction of the Exchange Agent that such tax has been paid
or is not payable.

   Any portion of the Merger Consideration made available to the Exchange Agent
pursuant to these procedures that remains unclaimed by Penederm Stockholders
twelve months after the Effective Time shall be returned to Mylan, upon demand,
and any such person who has not exchanged properly such person's Certificate or
Certificates for the Merger Consideration prior to that time shall thereafter
look only to Mylan for payment of the Merger Consideration. Notwithstanding the
foregoing, Mylan shall not be liable to any person for any amount paid to a
public official pursuant to applicable abandoned property laws.

   No dividends or other distributions with respect to securities of Mylan
constituting part of the Merger Consideration shall be paid to the holder of any
unsurrendered Certificates until such Certificates are properly surrendered.
Upon such surrender, there shall be paid, without interest, to the person in
whose name the Certificates representing the securities of Mylan into which such
Penederm Common Stock were converted are registered, all dividends and other
distributions payable in respect of such securities on a date subsequent to, and
in respect of a record date after, the Effective Time, less the amount of any
required withholding taxes.

                                       31
<PAGE>
 
   PENEDERM STOCKHOLDERS SHOULD NOT FORWARD STOCK CERTIFICATES TO THE EXCHANGE
AGENT UNTIL THEY HAVE RECEIVED TRANSMITTAL LETTERS. PENEDERM STOCKHOLDERS SHOULD
NOT RETURN STOCK CERTIFICATES WITH THE ENCLOSED PROXY.

Treatment of Options

   As of the Record Date, there were a total of _________ shares of Penederm
Common Stock subject to Penederm stock options.

   At the Effective Time, as required by the Merger Agreement, Mylan will assume
Penederm's Stock Option Plans and Penederm's rights and obligations under each
Penederm stock option that is outstanding immediately prior to the Effective
Time (an "Existing Option"). Under each Existing Option existing immediately
after the Effective Time (an "Assumed Option"), the optionee shall have the
right to receive from Mylan, in accordance with the terms and subject to the
conditions of the Existing Option, the number of shares of Mylan Common Stock
equal to the Exchange Ratio multiplied by the number of shares of Penederm
Common Stock that such optionee would have been entitled to receive had the
optionee exercised his or her Existing Option immediately prior to the Effective
Time, but only in accordance with the terms and conditions of the Existing
Option (including payment of the aggregate exercise price thereof, rounded up to
the nearest cent). No Assumed Option shall give the optionee any additional
benefits that the holder thereof did not have under the Existing Option; and the
terms of such Existing Options shall govern the vesting thereof including, if
applicable, any vesting of Existing Options as a result of the Merger. Each
Assumed Option shall constitute a continuation of the Existing Option,
substituting Mylan for Penederm and, in the case of employees, employment by a
Mylan company for employment by Penederm. Mylan has agreed to file, and maintain
the effectiveness of, a registration statement with the Commission covering the
Assumed Options.

Representations and Warranties

   Penederm and Mylan have made representations in the Merger Agreement relating
to, among other things: (a) each of Penederm's and Mylan's capitalization and
organization and similar corporate matters, (b) authorization, execution,
delivery and enforceability of the Merger Agreement and the Stock Option
Agreement, (c) conflicts under governing documents, required consents or
approvals, and violations of any agreements or law, (d) documents filed with the
Commission and the accuracy of information contained therein, (e) absence of
material adverse events, changes or effects, (f) brokers and finders, (g) tax
matters relating to the proposed Merger, (h) the absence of undisclosed
liabilities, (i) compliance with FDA laws, (j) litigation, (k) intellectual
property matters, and (l) the absence of contracts or disputes with labor unions
or organizations.

   Penederm has made additional representations, among others, relating to: (a)
compliance with law, including compliance with environmental and tax laws and
regulations, (b) retirement and other employee plans and matters, (c) the
disclosure and enforceability of certain material contracts, (d) certain
business matters relating to permits and licenses and insurance and accounts
receivables, (e) product warranties, and (f) liabilities with labor unions or
organizations.

   Mylan and Merger Sub made additional representations in the Merger Agreement
concerning Merger Sub relating to, among other things: (a) organization and
similar corporate matters, (b) authorization, execution, delivery and
enforceability of the Merger Agreement, conflicts under governing documents,
required consents or approvals, and violations of any agreements or law, and (c)
the absence of prior business authorities.

   None of the representations and warranties of Penederm, Mylan or Merger Sub
in the Merger Agreement described above will survive the Effective Time.

   In addition, Mylan and Penederm have made representations that serve as the
basis for the tax opinions of Buchanan Ingersoll and HEWM described under "THE
MERGER--Certain Federal Income Tax Consequences."

                                       32
<PAGE>
 
Conduct of Penederm's Business

   Penederm has covenanted to Mylan that, except as contemplated by the Merger
Agreement or agreed to in writing by Mylan, from the date of the Merger
Agreement to the Effective Time, Penederm will, and will cause its subsidiary
to, conduct its business in the ordinary course, consistent with past practice,
and will use commercially reasonable efforts to preserve its business
organization, its relationship with its customers and suppliers and maintain
satisfactory relationships with all persons with which it does business. In
addition, the Merger Agreement contains specific restrictions with respect to
certain matters.

Exclusivity

   Penederm has agreed that it will not, and will not authorize or permit its
subsidiary or any of their respective officers, directors, employees, counsel,
investment bankers, financial advisors, accountants, other representatives and
agents (collectively, the "Penederm Representatives") to, (A) solicit, initiate
or encourage (including by way of furnishing information), or take any other
action to facilitate, any inquiries or the making of any proposal which
constitutes, or may reasonably be expected to lead to, any Takeover Proposal (as
defined below); (B) participate in any discussion or negotiations regarding any
Takeover Proposal; (C) approve or agree to endorse any Takeover Proposal; (D)
enter into any agreement with respect to any Takeover Proposal; or (E) withdraw
or modify, or propose to withdraw or modify, in a manner adverse to Mylan, the
approval or recommendation of the Merger Agreement or the Merger, unless the
Penederm Board determines in good faith, after consulting with its legal
counsel, that it is necessary to withdraw or modify its recommendation because
of the occurrence of a Material Adverse Change with respect to Mylan, or the
occurrence of an event which has or could reasonably be expected to have a
Material Adverse Effect on Mylan (for the meaning of these terms, see "--
Conditions to the Merger"). Penederm and the Penederm Board may, however, at any
time prior to the Special Meeting, engage in the prohibited actions in response
to an unsolicited Takeover Proposal if, and only to the extent that, (x) the
Penederm Board determines in good faith, based upon the advice of its legal
counsel as to legal matters, that it is necessary to do so in order to comply
with its fiduciary duties to Penederm Stockholders under applicable law, (y) the
Penederm Board determines that the Takeover Proposal is a Superior Proposal (as
defined below), and (z) the party who submitted the Takeover Proposal executes a
customary confidentiality agreement.

   In addition, Penederm has agreed to advise promptly Mylan (orally and in
writing) of any Takeover Proposal received by Penederm or any request for
information stated by the proponent to be in contemplation of any Takeover
Proposal, or any inquiry which could reasonably be expected to lead to any
Takeover Proposal, the material terms and conditions of such Takeover Proposal
or request or inquiry and the identity of the person making such Takeover
Proposal, request or inquiry. Penederm has also agreed to keep Mylan reasonably
informed of any material amendment or modification to such Takeover Proposal,
request or inquiry.

   "Takeover Proposal" means any inquiry, proposal or offer from any person
relating to any: (A) tender or exchange offer, merger, consolidation or similar
transaction involving Penederm or its subsidiary; (B) sale, lease or other
disposition directly or indirectly by merger, consolidation, or share exchange
of assets of Penederm or its subsidiary representing 10% or more of the
consolidated assets of Penederm and its subsidiary; (C) issuance, sale or other
disposition of (including by way of merger, consolidation, share exchange or
similar transaction) securities (or options, rights or warrants to purchase, or
securities convertible into, such securities) representing 10% or more of the
voting power of Penederm; or (D) transaction in which any person shall acquire
beneficial ownership (as such term is defined in Rule 13d-3 under the Exchange
Act) or the right to acquire beneficial ownership of, or any "group" (as such
term is defined under the Exchange Act) shall have been formed which
beneficially owns or has the right to acquire beneficial ownership of, 25% or
more of the outstanding Penederm Common Stock.

   "Superior Proposal" means any Takeover Proposal on terms which the Penederm
Board determines in its good-faith judgment, based in part on the advice of a
financial advisor of nationally recognized reputation, to be more favorable to
the Penederm Stockholders than the Merger from a financial point of view and for
which financing is then committed or reasonably likely to be available.

                                       33
<PAGE>
 
Resales of Mylan Common Stock

   All Mylan Common Stock received by Penederm Stockholders in the Merger will
be freely transferable pursuant to the Securities Act, except that Mylan Common
Stock received by persons who are deemed to be "affiliates" (as such term is
defined under the Securities Act) of Penederm at the time that Penederm
Stockholders vote on the Merger may be resold only in transactions permitted by
the resale provisions of Rule 145 promulgated under the Securities Act or as
otherwise permitted under the Securities Act. Under the Merger Agreement,
Penederm intends to designate its directors and executive officers as its
affiliates for purposes of these restrictions and the requirement of the Merger
Agreement that its affiliates sign letters acknowledging these restrictions.
Each Penederm affiliate has executed a written agreement agreeing to comply with
the requirements of the Securities Act (the "Affiliate Letter").

Conditions to the Merger

   The respective obligations of Penederm, Mylan and Merger Sub to effect the
Merger are subject to the fulfillment at or prior to the Effective Time of the
following conditions:

   (a) The Merger Agreement and the Merger shall have been approved and adopted
       by the requisite vote of the Penederm Stockholders;

   (b) All required governmental approvals and contractual consents shall have
       been obtained, and the applicable waiting period under the HSR Act shall
       have expired;

   (c) The Registration Statement shall have become effective under the
       Securities Act and shall not be the subject of any stop order or
       proceeding seeking a stop order;

   (d) The Mylan Common Stock issued in the Merger shall have been approved for
       listing on the NYSE upon official notice of issuance; and

   (e) No legal restraint or prohibition preventing the consummation of the
       Merger shall be in effect.

   The obligations of Penederm to effect the Merger are subject to the
satisfaction or waiver on or before the Effective Time of each of the following
additional conditions:

   (a) No event or circumstance shall have occurred which has or is reasonably
       expected to have a Material Adverse Effect (as defined below) on Mylan
       and its subsidiaries taken as a whole, including, without limitation,
       such event or occurrence caused by: (i) the failure of representations
       and warranties of Mylan and Merger Sub contained in the Merger Agreement
       to continue to be true and correct on and as of the date on which the
       Effective Time occurs, except for changes contemplated in the Merger
       Agreement, with the same force and effect as if made on and as of the
       Effective Date; (ii) the failure of Mylan or Merger Sub to have performed
       or complied with all agreements, conditions and covenants required by the
       Merger Agreement to be performed or complied with by them on or before
       the Effective Date; or (iii) the execution, delivery and performance by
       Mylan of the Merger Agreement and the consummation of the Merger
       resulting in or constituting an event of default under an obligation
       under any agreement of Mylan;

   (b) There shall have been no Material Adverse Change (as defined below) with
      respect to Mylan;

   (c) Penederm shall have received a certificate of an executive officer of
       each of Mylan and Merger Sub certifying as to compliance with the
       conditions set forth in clauses (a) and (b) above;

   (d) Penederm shall have received an opinion of HEWM to the effect that, among
       other things, the Merger will constitute a reorganization within the
       meaning of Section 368(a) of the Code and that Mylan, Merger Sub and
       Penederm shall each be a party to that reorganization within the meaning
       of Section 368(b) of the Code; and

                                       34
<PAGE>
 
   (e) Penederm shall have received from Mylan a certificate confirming certain
       representations and covenants of Mylan contained in the Merger Agreement
       with respect to tax matters relating to the status of the Merger as a
       reorganization within the meaning of Section 368(a) of the Code.

   The obligations of Mylan and Merger Sub to effect the Merger are subject to
the satisfaction or waiver on or before the Effective Time of each of the
following additional conditions:

   (a) No event or circumstance shall have occurred which has or is reasonably
       expected to have a Material Adverse Effect on Penederm, including,
       without limitation, such event or occurrence caused by: (i) the failure
       of representations and warranties of Penederm contained in the Merger
       Agreement to be true and correct on and as of the Effective Date, except
       for changes contemplated in the Merger Agreement, with the same force and
       effect as if made on and as of the Effective Date; (ii) the failure of
       Penederm to have performed or complied with all agreements, conditions
       and covenants required by the Merger Agreement to be performed or
       complied with by Penederm on or before the Effective Date; or (iii) the
       execution, delivery and performance of the Merger Agreement and the
       consummation of the Merger resulting in or constituting an event of
       default under  an obligation under any agreement of Penederm;

   (b) There shall have been no Material Adverse Change with respect to
       Penederm;

   (c) Mylan shall have received a certificate of an executive officer of
       Penederm certifying as to compliance with the conditions set forth in
       clauses (a) and (b) above;

   (d) Mylan shall have received an opinion of Buchanan Ingersoll to the effect
       that, among other things, the Merger will constitute a reorganization
       within the meaning of Section 368(a) of the Code and that Mylan, Merger
       Sub and Penederm shall each be a party to that reorganization within the
       meaning of Section 368(b) of the Code;

   (e) Mylan shall have received from Penederm a certificate confirming certain
       representations and covenants of Penederm contained in the Merger
       Agreement with respect to tax matters relating to the status of the
       Merger as a reorganization within the meaning of Section 368(a) of the
       Code; and

   (f) No shares of preferred stock of Penederm shall be issued or outstanding.

   "Material Adverse Change" or "Material Adverse Effect" means, when used in
the Merger Agreement with respect to Mylan and Penederm, as the case may be, any
event, circumstance, change or effect that is or could reasonably be expected
(as far as can be foreseen at the time) to be so adverse as to result in a
severe and critical impairment of the business, assets, liabilities, financial
condition or results of operations of Mylan and its subsidiaries, taken as a
whole, or Penederm and its subsidiary, taken as a whole, as the case may be.

Termination of the Merger Agreement

   Under the Merger Agreement, Penederm, on the one hand, and Mylan or Merger
Sub, on the other hand, is entitled to abandon the Merger and terminate the
Merger Agreement if the conditions to its respective obligations to effect the
Merger (see "--Conditions to the Merger") shall not have been satisfied or
waived in writing on November 30, 1998.

   In addition, the Merger may be abandoned and the Merger Agreement may be
terminated at any time on or before the Effective Time, whether before or after
approved by Penederm Stockholders:

(a)  by mutual agreement of the Penederm Board and the Boards of Directors of
     each of Mylan and Merger Sub;
(b)  by either Mylan or Merger Sub, on the one hand, or Penederm, on the other,
     if the consummation of the Merger would violate any preliminary injunction
     or restraining order or final and nonappealable order, decree, injunction
     or restraining order or judgment of any United States court or other
     tribunal of competent jurisdiction;

                                       35
<PAGE>
 
(c)  by Mylan if any of the following shall have occurred: (i) any person (other
     than Mylan or any subsidiary of Mylan) shall have commenced (as such term
     is defined in Rule 14d-2 under the Exchange Act), a tender offer or
     exchange offer to purchase any Penederm Common Stock or securities
     convertible into such shares such that, upon consummation of such offer,
     such person would own or control 50% or more of the then outstanding
     Penederm Common Stock and the Penederm Board, within ten business days
     after such tender or exchange offer shall have been so commenced, fails to
     recommend against acceptance of such tender or exchange offer by its
     stockholders; (ii) Penederm or its subsidiary shall have authorized,
     recommended, proposed or publicly announced an intention to authorize,
     recommend or propose, or entered into, an agreement with any person (other
     than Mylan or any subsidiary of Mylan) to (A) effect a merger,
     consolidation or similar transaction involving Penederm or its subsidiary,
     (B) sell, lease or otherwise dispose of assets of Penederm or its
     subsidiary representing 10% or more of the consolidated assets of Penederm,
     (C) issue, sell or otherwise dispose of (including by way of merger,
     consolidation, share exchange or any similar transaction) securities (or
     options, rights or warrants to purchase), or securities convertible into,
     such securities) representing 10% or more of the voting power of Penederm,
     or (D) grant to such person a license of any intellectual property of
     Penederm other than licenses in the ordinary course of business relating to
     the sale of Penederm's products; (iii) any Person (other than Mylan or any
     subsidiary of Mylan) shall have acquired beneficial ownership (as such term
     is defined in Rule 13d-3 under the Exchange Act) or the right to acquire
     beneficial ownership of, or any "group" (as such term is defined under the
     Exchange Act) shall have been formed which beneficially owns or has the
     right to acquire beneficial ownership of, 25% or more of the then
     outstanding Penederm Common Stock; or (iv) the Penederm Board shall have
     withdrawn or modified in a manner adverse to Mylan the recommendation of
     the Penederm Board that the Penederm Stockholders approve the Merger
     Agreement and the Merger;

(d)  by Penederm in connection with entering into an agreement for a Superior
     Proposal as expressly permitted by the Merger Agreement (see "--
     Exclusivity") provided that (i) immediately following such termination
     Penederm executes a definitive agreement to implement such Superior
     Proposal, (ii) prior to any such termination, (x) Penederm shall have
     provided Mylan with four days' notice of the terms of the Superior Proposal
     and (y) Penederm shall, have, and shall have caused its financial and legal
     advisors to have, negotiated in good faith with Mylan with respect to any
     proposal made by Mylan to adjust the terms of the Merger Agreement as would
     enable Penederm, consistent with the fiduciary duties of the Penederm
     Board, to proceed with the Merger, and (iii) Penederm shall have paid Mylan
     the Termination Fee;

(e)  by either Mylan or Penederm if the Merger shall not have been consummated
     on or before November 30, 1998, provided that the right to terminate the
     Merger Agreement on this basis shall not be available to any party whose
     failure to fulfill any obligation under the Merger Agreement has been the
     cause of, or resulted in, the failure of the Effective Time to occur on or
     before November 30, 1998; or

(f)  by Penederm, 10 days after the Special Meeting, if at the Special Meeting
     the Merger Agreement and the Merger shall fail to be approved and adopted
     by the affirmative vote of the Penederm Stockholders as required under the
     DGCL.

Termination Fee; Expenses of the Merger

   If the Merger Agreement is terminated, it shall forthwith become void, but
each party shall be entitled to pursue all of its remedies for any prior breach.

   Except as described below with respect to the Termination Fee, each party is
required by the Merger Agreement to bear all of its own costs and expenses in
connection with the Merger Agreement and the transactions contemplated thereby,
whether or not the Merger is consummated, other than the costs of printing and
mailing this Proxy Statement/Prospectus, which shall be shared equally.

   Penederm is required by the Merger Agreement to pay Mylan a termination fee
(the "Termination Fee") equal to $9 million within two business days of the
occurrence of any of the following events:

                                       36
<PAGE>
 
(a)  Mylan terminates the Merger Agreement on the basis described in paragraph
     (c)(i) under "--Termination of the Merger Agreement," or Mylan had the
     right so to terminate at the time the Merger Agreement was otherwise
     terminated, and within 12 months after such termination Penederm executes a
     definitive agreement to implement a Takeover Proposal (whether or not such
     Takeover Proposal triggered Mylan's termination right);

(b)  Mylan terminates the Merger Agreement on the basis described in paragraph
     (c)(ii) under "--Termination of the Merger Agreement," or Mylan had the
     right so to terminate at the time the Merger Agreement is otherwise
     terminated;

(c)  Mylan terminates the Merger Agreement on the basis described in paragraph
     (c)(iv) under "--Termination of the Merger Agreement," or Mylan had the
     right so to terminate at the time the Merger Agreement is otherwise
     terminated, except that Penederm is not obligated to pay Mylan the
     Termination Fee under those conditions in the event that (i) such actions
     of the Penederm Board that gave rise to Mylan's right to terminate on that
     basis were the result of an event which had, or was reasonably expected to
     have, a Material Adverse Effect on Mylan or had caused, or was reasonably
     expected to cause, Mylan to suffer a Material Adverse Change, and (ii) the
     Penederm Board made a good-faith determination, based on the advice of its
     legal counsel as to legal matters, that such actions were necessary in
     order to comply with its fiduciary duties to Penederm Stockholders under
     applicable law;

(d)  Penederm terminates the Merger Agreement on the basis described in
     paragraph (d) under "--Termination of the Merger Agreement";

(e)  Either Mylan or Penederm terminates the Merger Agreement, following a
     Takeover Proposal, on the basis described in paragraph (e) under "--
     Termination of the Merger Agreement" and within 12 months after such
     termination Penederm executes with a third party a definitive agreement to
     implement a Takeover Proposal; or

(f)  Penederm terminates the Merger Agreement, following a Takeover Proposal, on
     the basis set forth in paragraph (f) under "--Termination of the Merger
     Agreement" and within 12 months after such termination Penederm executes
     with a third party a definitive agreement to implement a Takeover Proposal.

Benefit Plans

   The Merger Agreement provides that the eligibility of Penederm employees (and
their spouses and dependents) to participate in the combined company's welfare
benefit plans after the Effective Time will be determined without regard to any
exclusion or condition to which the employee is not subject under any similar
Penederm plan. Participants in Penederm's welfare benefit plans will receive
credit, under the welfare benefit plan of the combined company in which they
participate after the Effective Time, toward annual co-insurance and deductible
limitations and requirements for any payments made for eligible charges incurred
by them during the calendar year in which the Effective Time occurs, under the
applicable welfare plan of Penederm. In addition, all employees of Penederm
following the Effective Time will receive credit, for purposes of determining
vesting the eligibility under retirement, welfare, vacation and similar plans or
policies, for service with Penederm prior to the Effective Date. All Penederm
employees immediately prior to the Effective Time will be eligible to
participate in the combined company's employment severance programs, and for the
purposes of such programs will receive credit for service with Penederm prior to
the Effective Date.

The Stock Option Agreement

   The Option

   In order to induce Mylan to enter into the Merger Agreement, Penederm entered
into the Stock Option Agreement at Mylan's request. Pursuant to the Stock Option
Agreement, Mylan has been granted the Mylan Option, which gives Mylan the right
to purchase the Option Shares (approximately 19.9% of the outstanding Penederm

                                       37
<PAGE>
 
Common Stock as of June 24, 1998 prior to giving effect to the exercise of the
Mylan Option) at the Option Price ($20 per Option Share, subject to adjustment
under specified circumstances). The Mylan Option was a condition to Mylan's
entering into the Merger Agreement, and it might increase the likelihood of
consummation of the Merger by discouraging competing offers for Penederm.
Certain aspects of the Stock Option Agreement may have the effect of
discouraging persons who may now, or prior to the Effective Time, be interested
in acquiring all of or a significant interest in Penederm from considering or
proposing such an acquisition, even if such persons were prepared to offer to
pay consideration to Penederm Stockholders that had a higher current market
price than the shares of Mylan Common Stock to be received for each share of
Penederm Common Stock pursuant to the Merger Agreement. In addition, if Mylan
were to become entitled to, and did, exercise the Mylan Option, such exercise
could preclude a third party from acquiring Penederm in a transaction intended
to be accounted for as a pooling of interests, and the potential for such
preclusion could further discourage competing offers for Penederm. The Stock
Option Agreement is in effect and is not conditioned on approval by the Penederm
Stockholders.

   The Mylan Option may be exercised by Mylan, in whole or in part, at any time,
or from time to time, following the occurrence of one of the Purchase Events
described in the following paragraph. Mylan may exercise the Mylan Option by
paying the Option Price in cash and receiving the Option Shares (which exercise
requires the satisfaction of certain additional conditions).

   Purchase Events

   The Mylan Option may be exercised on the occurrence of at least one of the
following "Purchase Events":

 

(a)  any of the following occurs prior to the earlier of the Effective Time or
     the termination of the Merger Agreement in accordance with its terms: (i)
     any person (other than Mylan or any of its subsidiaries) shall have
     commenced (as such term is defined in Rule 14d-2 under the Exchange Act) a
     tender offer, or shall have filed a registration statement under the
     Securities Act with respect to an exchange offer, to purchase any shares of
     Penederm Common Stock such that, upon consummation of such offer, such
     person or a "group" (as such term is defined under the Exchange Act) of
     which such person is a member shall have acquired beneficial ownership (as
     such term is defined in Rule 13d-3 of the Exchange Act), or the right to
     acquire beneficial ownership, of 25% or more of the then outstanding
     Penederm Common Stock; (ii) Penederm or any of its subsidiaries shall have
     authorized, recommended, proposed or publicly announced an intention to
     authorize, recommend or propose, or entered into, an agreement including,
     without limitation, an agreement in principle, with any person (other than
     Mylan or any of its subsidiaries) to effect or provide for a Takeover
     Proposal; (iii) any person (other than Mylan or any of its subsidiaries)
     shall solicit proxies or consents or announce a bona fide intention to
     solicit proxies or consents from the Penederm Stockholders (x) in
     opposition to the Merger, the Merger Agreement or any related transactions
     or (y) relating to a Takeover Proposal (other than solicitations of
     stockholders seeking approval of the Merger, the Merger Agreement or any
     related transactions), and the Penederm Stockholders shall have failed to
     approve the Merger; or (iv) any person (other than Mylan or any of its
     subsidiaries) shall have acquired beneficial ownership (as such term is
     defined in Rule 13d-3 under the Exchange Act) or the right to acquire
     beneficial ownership of, or any "group" (as such term is defined under the
     Exchange Act) shall have been formed which beneficially owns or has the
     right to acquire beneficial ownership of, Penederm Common Stock (other than
     trust account shares) aggregating 25% or more of the then outstanding
     Penederm Common Stock;

(b)  the termination of the Merger Agreement under circumstances entitling Mylan
     to immediate payment of the Termination Fee pursuant to the Merger
     Agreement (see "--Termination of the Merger Agreement");

(c)  the execution by Penederm, within 12 months of a termination of the Merger
     Agreement (i) by either Mylan or Penederm on the basis described in
     paragraph (e) under "--Termination of the Merger Agreement" or (ii) by
     Penederm on the basis described in paragraph (f) under "--Termination of
     the Merger Agreement," of a definitive agreement to implement a Takeover
     Proposal with a third party who had submitted a Takeover Proposal prior to
     such termination (a "Proponent"); or

                                       38
<PAGE>
 
(d)  the execution by Penederm, within six months of a termination of the Merger
     Agreement on the basis described in clause (c), of a definitive agreement
     to implement a Takeover Proposal with a third party who is not a Proponent,
     provided Penederm had received a Takeover Proposal from a Proponent prior
     to such termination.

   Mylan's "Put" Rights

   The Stock Option Agreement gives Mylan the right to "put" the Mylan Option
(unless it has expired or terminated) and all Option Shares that have previously
been purchased by Mylan and are still owned by it back to Penederm, and thereby
obligate Penederm to repurchase the Mylan Option and such Option Shares, for a
six-month period commencing upon the first occurrence of a "Repurchase Event,"
as defined in the Stock Option Agreement. The "Put Price" payable by Penederm
upon Mylan's exercise of such put right is the sum of: (i) the aggregate Option
Price paid by Mylan for all Option Shares previously purchased by Mylan that are
still owned by it; (ii) the excess (if any) of the average of the last sales
prices for Penederm Common Stock on NASDAQ for the ten preceding trading days
(the "Market Price") over the aggregate Option Price referred to in clause (i),
multiplied by the number of Option Shares that are still owned by Mylan; and
(iii) the excess (if any) of the Market Price over the Option Price, multiplied
by the number of Option Shares with respect to which the Mylan Option has not
been exercised.

   Mylan's Registration Rights

   The Stock Option Agreement provides that if Mylan desires to sell any of the
Option Shares, Penederm will cooperate with Mylan and any underwriters in
registering such Option Shares for resale including, without limitation,
promptly filing a registration statement which complies with the requirements of
applicable federal and state securities laws. Penederm is not required to have
declared effective more than two such registration statements.

   Termination

   The Stock Option Agreement provides that the Mylan Option will terminate and
be of no further force and effect upon the earliest to occur of (a) the
Effective Time, (b) 12 months after the first occurrence of a Purchase Event of
the type described in subclause (a) or (b) under "--Purchase Events" above and
(c) six months after the first occurrence of a Purchase Event of the type
described in subclause (c) or (d) under "--Purchase Events" above.
Notwithstanding the termination of the Mylan Option, Mylan will be entitled to
purchase the Option Shares if it has exercised the Mylan Option in accordance
with the terms hereof prior to the termination of the Mylan Option and the
termination of the Mylan Option shall not affect any rights hereunder which by
their terms do not terminate or expire prior to or as of such termination.

   Profit Limitation

   Under the Stock Option Agreement, in no event shall Mylan's "Total Profit"
(as hereinafter defined) exceed $24 million (the "Cap"), and if Total Profit
otherwise would exceed the Cap, Mylan, at its sole election, shall either (a)
deliver to Penederm for cancellation Option Shares previously purchased by Mylan
valued at the average of the last sales price for Penederm Common Stock on
NASDAQ for the ten trading days ending on the day immediately preceding such
delivery), (b) pay cash to Penederm, or (c) undertake any combination thereof,
so that Total Profit shall not exceed the Cap after taking into account the
foregoing actions.

   As used herein, the term "Total Profit" shall mean the aggregate amount
(before taxes) of the following: (i) the amount of cash paid or payable by Mylan
as the Termination Fee pursuant to the Merger Agreement; (ii) (x) the amount
paid or payable by Mylan pursuant to the Penederm's repurchase of Option Shares
pursuant to the Stock Option Agreement, less (y) Mylan's purchase price for such
Option Shares; and (iii) (x) the net cash amounts received by Mylan pursuant to
the sale of Option Shares (or any other securities into which such Option Shares
are converted or exchanged) to any unaffiliated party, less (y) Mylan's purchase
price for such Option Shares.

                                       39
<PAGE>
 
The Voting Agreements

   Voting and Proxies

   In order to induce Mylan to enter into the Merger Agreement, each director of
Penederm (in his capacity as a Penederm Stockholder and without limiting or
affecting his obligations as a director) has entered into a voting agreement at
Mylan's request. Pursuant to and during the term of the Voting Agreements, each
director of Penederm has agreed, to vote (or cause to be voted) all of the
Penederm Common Stock beneficially owned by such director and all shares
subsequently acquired by such holder (i) to adopt and approve the Merger and the
Merger Agreement and the approval of the other transactions contemplated by the
Merger Agreement at any meeting of Penederm Stockholders at which such matters
are considered and at every adjournment or postponement thereof and (ii) against
(a) any merger agreement or merger (other than the Merger Agreement and the
Merger), consolidation, combination, sale of substantial assets, reorganization,
recapitalization, dissolution, liquidation or winding up, of or by Penederm, or
any other Takeover Proposal (collectively, "Alternative Transactions") or (b)
any amendment of Penederm's certificate of incorporation ("Penederm's
Certificate") or Penederm's bylaws ("Penederm's Bylaws") or other proposal or
transaction involving Penederm or its subsidiary, which would in any manner
impede, frustrate, prevent or nullify the Merger, the Merger Agreement or any of
the other transactions contemplated by the Merger Agreement (collectively,
"Frustrating Transactions"). In addition, each such director (in his capacity as
a Penederm Stockholder) has granted Mylan an irrevocable proxy to vote shares of
Penederm Common Stock held by such director (i) in favor of the Merger and the
Merger Agreement and (ii) against any Alternative Transactions or Frustrating
Transactions. The Voting Agreements terminate upon the earlier of the Effective
Time or termination of the Merger Agreement in accordance with its terms. See "-
- -Exclusivity."

   The aggregate number of shares of Penederm Common Stock which is subject to
the Voting Agreements is 331,656, or approximately 3.8% of the shares of
Penederm Common Stock outstanding on the Record Date. See, however, "--Alternate
Voting Agreement" for information about circumstances in which the 270,091
shares subject to a Voting Agreement with one director, whose shares of Penederm
Common Stock represent approximately 3.1% of the shares of Penederm Common Stock
outstanding on the Record Date, will cease to be bound by the voting obligations
of such Alternate Voting Agreement.

   Prohibited Actions

   Each director has also agreed (in his capacity as a Penederm Stockholder)
that he will not (i) sell, transfer, pledge, assign or otherwise dispose of, or
enter into any contract, option or other arrangement (including any profit
sharing arrangement) or understanding with respect to the sale, transfer,
pledge, assignment or other disposition of, Penederm Common Stock to any person
other than Mylan or Mylan's designee, (ii) enter into any voting arrangement,
whether by proxy, voting agreement, voting trust, power-of-attorney or
otherwise, with respect to Penederm Common Stock, or (iii) take any other action
that would in any way restrict, limit or interfere with the performance of such
director's obligations under his Voting Agreement or the transactions
contemplated thereby; provided, however, that he may transfer all or part of his
securities of Penederm to any sibling or any other member of his immediate
family or lineal descendants or any trust for the benefit of any of them, so
long as the recipient of the Penederm securities agrees to be bound by the
Voting Agreement.

   Alternate Voting Agreement

   All of the 270,091 outstanding shares of Penederm Common Stock beneficially
owned by one of Penederm's directors are held by him in his capacity as the
general partner of a partnership which is in turn the general partner of an
investment fund. Such shares are owned by the investment fund, which is
scheduled by its governing agreement to be wound up on September 15, 1998. To
facilitate such winding-up and the related distribution of the shares of
Penederm Common Stock owned by such investment fund to its individual investors,
Mylan has entered into an Alternate Voting Agreement with the applicable
director permitting him to effect such distribution as close to September 15,
1998 as is consistent with the fund's obligation to effect the distribution, at
which point he will cease to be bound by the voting obligations of the Alternate
Voting Agreement as to the distributed shares, his irrevocable proxy in favor of
Mylan will terminate as to those shares and the individual distributees will be
free to vote the distributed shares as they choose. Accordingly, if the vote on
the Merger Agreement by the Penederm

                                       40
<PAGE>
 
Stockholders occurs after the distribution, there is no assurance as to how
those shares, which constitute approximately 3.1% of the shares of Penederm
Common Stock outstanding on the Record Date, will be voted thereon.


   Other Provisions

   Each Voting Agreement also contains provisions relating to, among other
things, representations and warranties by the applicable director (in his
capacity as a Penederm Stockholder) and specific enforcement of his Voting
Agreement.

Co-Promotion Agreements

   In December 1997, Penederm and Bertek entered into the Mentax(R) Co-Promotion
Agreement to market Mentax(R) in the United States to primary care physicians
who are called on by members of Bertek's sales force (the "Bertek Audience").
Pursuant to the Mentax(R) Co-Promotion Agreement, Bertek receives a portion of
the profit Penederm earns in connection with revenues generated from
prescriptions written by the Bertek Audience. The initial term of the Mentax(R)
Agreement is four years.

   In July 1998, Penederm and Bertek entered into the Avita(R) Co-Promotion
Agreement, pursuant to which Bertek will co-promote Avita(R) in the United
States to primary care physicians. The terms of the Avita(R) Co-Promotion
Agreement are similar to those of the Mentax(R) Co-Promotion Agreement, except
that the Avita(R) Co-Promotion Agreement provides for a nonrefundable up-front
license fee and an advance on Penederm's share of the profits generated from
revenues on prescriptions written by the Bertek Audience.

   Both the Mentax(R) Co-Promotion Agreement and the Avita(R) Co-Promotion
Agreement are in effect, are independent of the Merger Agreement, are not
conditioned on approval by the Penederm Stockholders and will survive the
termination of the Merger Agreement.

                         COMPARISON OF SHAREHOLDER RIGHTS

   If the Merger is consummated, holders of Penederm Common Stock will become
holders of Mylan Common Stock, which will result in their rights as shareholders
being governed by the laws of the Commonwealth of Pennsylvania and the Amended
and Restated Articles of Incorporation of Mylan ("Mylan's Articles") and the
Bylaws of Mylan ("Mylan's Bylaws"). The rights of holders of Penederm Common
Stock currently are governed by the laws of the State of Delaware and by
Penederm's Certificate and Penederm's Bylaws.

   It is not practicable to describe all of the differences between the laws of
the Commonwealth of Pennsylvania and the laws of the State of Delaware, between
Mylan's Articles and Penederm's Certificate and between Mylan's Bylaws and
Penederm's Bylaws. The following is a summary of certain differences between the
rights of a holder of Penederm Common Stock and the rights of a holder of Mylan
Common Stock.

Shareholder Rights Generally

   Notice of Meetings. Under the Pennsylvania Business Corporation Law of 1988,
as amended (the "PBCL"), holders of Mylan Common Stock are entitled to at least
10 days' prior written notice for a meeting called to consider a fundamental
change (as defined in the PBCL) and five days' prior written notice for any
other meeting. Under the DGCL and Penederm's Bylaws, holders of Penederm Common
Stock are entitled to at least 10 days' prior written notice for a special
meeting called to consider general matters. Under the DGCL, at least 20 days'
notice is required to consider a merger.

   Proxies. Under the DGCL and Penederm's Bylaws, a proxy is invalid after three
years from its date, unless the proxy provides for a longer period. Under the
PBCL, there are no limitations on the duration of proxies except that an
unrevoked proxy is not valid after three years unless a longer time is expressly
provided therein.

                                       41
<PAGE>
 
   Right to Call Special Meetings. Under the PBCL, holders of Mylan Common Stock
have no right to call special meetings of shareholders except that an interested
shareholder (i.e., the beneficial owner of at least 20% of the corporation's
outstanding voting securities) has the right to call a special meeting of
shareholders to approve certain business combinations. Under the DGCL, a special
meeting of stockholders may be called only by the Penederm Board or by such
person or persons as may be authorized by Penederm's Certificate or Penederm's
Bylaws. Under Penederm's Certificate and Penederm's Bylaws, the Chairman of the
Board or the President may call a special meeting of stockholders, but business
transacted must be limited to that stated in the notice of such meeting.

Shareholder Voting Rights

   General Vote Required. Under the PBCL, corporate action taken by
shareholders, including shareholder action to amend the articles of
incorporation or to approve mergers, consolidations or dissolution, generally is
authorized upon receiving the affirmative vote of a majority of the votes cast
by all shareholders entitled to vote thereon (and, if any class of shares is
entitled to vote thereon as a class, the affirmative vote of a majority of the
votes cast in such class). Under the DGCL and Penederm's Bylaws, the affirmative
vote of the holders of a majority of the stock having voting power present in
person or represented by proxy at a meeting at which a quorum is present is
required for stockholder action unless the DGCL requires otherwise. Under the
DGCL, the affirmative vote of the majority of the outstanding shares entitled to
vote thereon generally is required to effect mergers or consolidations.

   Special Vote Required for Certain Business Combinations. Mylan's Articles
require the affirmative vote of at least 75% of the outstanding shares of Mylan
Common Stock entitled to vote in order to effect certain business combinations.
See "DESCRIPTION OF MYLAN CAPITAL STOCK--Special Considerations."

   In addition, Mylan is subject to provisions of the PBCL regarding business
combinations. The PBCL prohibits certain business combinations (as defined in
the PBCL) involving a Pennsylvania corporation that has shares registered under
the Exchange Act and an "interested shareholder" unless one of the five
conditions described below is satisfied or an exemption is found. An "interested
shareholder" is generally defined to include a person who beneficially owns at
least 20% of the votes that all shareholders would be entitled to cast in an
election of directors of the corporation.

   In general, a corporation can effect a business combination involving an
interested shareholder under the PBCL if one of the following five conditions is
satisfied: (i) prior to the date on which the person becomes an interested
shareholder, the board of directors approves the business combination or the
purchase of shares that causes the person to become an interested shareholder;
(ii) the business combination is approved by an affirmative vote of the holders
of all outstanding shares; (iii) the business combination is approved by a
majority of the disinterested shareholders at a meeting called at least five
years after the date the person becomes an interested shareholder; (iv) the
interested shareholder holds 80% or more of the votes that all shareholders
would be entitled to cast in an election of directors of the corporation and the
business combination is approved by a majority of the disinterested shareholders
at a meeting held at least three months after the interested shareholder
acquired such 80% interest, provided that the fair price and procedural
requirements set forth in the PBCL are satisfied; or (v) the business
combination is approved by the shareholders at a meeting called at least five
years after the date the person becomes an interested shareholder, provided that
the fair price and procedural requirements set forth in the PBCL are satisfied.

   The DGCL prohibits certain business combinations (as defined in the DGCL)
between a Delaware corporation that has shares listed on a national stock
exchange, authorized for quotation on The NASDAQ Stock Market or held of record
by more than 2,000 stockholders and an interested stockholder that occur within
three years of the time that such stockholder became an interested stockholder,
unless one of three conditions is satisfied or an exemption is found. An
"interested stockholder" is generally defined to include a person who
beneficially owns at least 15% of the voting stock of the corporation. In
general, a corporation can effect a business combination involving an interested
stockholder under the DGCL within three years of the time that such stockholder
became an interested stockholder if one of the following three conditions is
satisfied: (i) prior to such time, the board of directors approves the business
combination or the transaction that causes the person to become an interested
stockholder; (ii) upon consummation of the transaction which resulted in the
stockholder becoming an interested stockholder, the

                                       42
<PAGE>
 
interested stockholder owned at least 85% of the voting stock at the time the
transaction commenced; or (iii) at or subsequent to such time the business
combination is approved by the board of directors and authorized by the
affirmative vote of two-thirds of the disinterested shareholders.

   Merger or Consolidation Without Shareholder Approval. Under the PBCL, no vote
of the shareholders of a corporation is required to approve a merger or
consolidation if (i) the plan does not alter the corporation's status as a
Pennsylvania corporation or in any respect its articles of incorporation and
each share of its capital stock is to continue as or be converted into an
identical share of the surviving corporation; or (ii) another corporation
directly or indirectly owns 90% or more of shares of each class of the
corporation.

   Under the DGCL, no vote of the stockholders of a corporation is required to
approve a merger or consolidation if (i) the plan does not amend in any respect
the corporation's certificate of incorporation; (ii) each share of its capital
stock is to continue as or be converted into an identical share of the surviving
corporation; or (iii) either no stock of the surviving corporation is to be
issued under the plan or the treasury or unissued authorized shares of the
surviving corporation to be issued plus those shares issuable upon conversion of
other shares to be issued in the merger do not exceed 20% of the outstanding
shares of such corporation immediately prior to the merger.

Shareholder Appraisal Rights

   Under the DGCL, a stockholder of a corporation who does not vote in favor of
certain merger transactions and who demands appraisal of his shares in
connection therewith may, under varying circumstances, be entitled to appraisal
rights pursuant to which such stockholder may receive cash in the amount of the
fair value of his shares (as determined by a Delaware court) in lieu of the
consideration he would otherwise receive in the transaction. Unless the
corporation's certificate of incorporation provides otherwise, such appraisal
rights are not available in certain circumstances, including without limitation
(a) the sale, lease or exchange of all or substantially all of the assets of a
corporation, (b) the merger or consolidation by a corporation the shares of
which are either listed on a national securities exchange or the NASDAQ National
Market or are held of record by more than 2,000 holders if such stockholders
receive only shares of the surviving corporation or shares of any other
corporation which are either listed on a national securities exchange or the
NASDAQ National Market or held of record by more than 2,000 holders, plus cash
in lieu of fractional shares or (c) to stockholders of a corporation surviving a
merger if no vote of the stockholders of the surviving corporation is required
to approve the merger because the merger agreement does not amend the existing
certificate of incorporation, each share of the surviving corporation
outstanding prior to the merger is an identical outstanding or treasury share
after the merger, and the number of shares to be issued in the merger does not
exceed 20% of the shares of the surviving corporation outstanding immediately
prior to the merger and if certain other conditions are met.

   Under the PBCL, a shareholder of a corporation has the right, under varying
circumstances, to dissent from certain corporate transactions (including
mergers, share exchanges, the sale of all or substantially all of the corporate
assets and corporate divisions) and to obtain payment in cash of the fair value
of his shares in lieu of the consideration he would otherwise receive in the
transaction. Such dissenters rights are not available where the shares held by
the shareholder are either listed on a national securities exchange or are held
of record by more than 2,000 shareholders. Notwithstanding this limitation, the
PBCL provides that the bylaws or a resolution of the board of directors may
direct that all or part of the shareholders shall have dissenters' rights in
connection with any corporate transaction that would not otherwise entitle such
shareholder to dissenters' rights. Mylan's Bylaws do not include such a
provision nor has the Board of Directors of Mylan adopted such a resolution.

   The concept of "fair value" in payment for shares upon exercise of appraisal
rights is different under the DGCL and the PBCL. Under the DGCL, "fair value"
must be determined exclusive of any element of value arising from the
accomplishment or expectation of the relevant transaction. The PBCL provides
that the fair value of shares must be determined immediately before the
effectuation of the corporate action to which the dissenter objects taking into
account all relevant factors, but excluding any appreciation or depreciation in
anticipation of the corporate action.

                                       43
<PAGE>
 
Rights With Respect to Shares

   Dividends; Purchases and Redemptions of Shares. Under the PBCL, Mylan may pay
dividends and make stock purchases and redemptions unless, after giving effect
to the distribution: (i) the corporation would be unable to pay its debts as
they become due in the usual course of its business, or (ii) the total assets of
the corporation would be less than the sum of its total liabilities plus the
amount that would be needed, if the corporation were to be dissolved at the time
of distribution, to satisfy the preferential rights upon dissolution of
stockholders whose preferential rights are superior to those receiving the
distribution. The Board of Directors of Mylan may base its determination of
total assets and total liabilities on any factors it considers relevant,
including the book values of the corporation's assets and liabilities as
reflected on its books and records, unrealized appreciation and depreciation of
the corporation's assets or the current value of the corporation's assets and
liabilities, either valued separately or valued in segments or as an entirety as
a going concern.

   The DGCL provides that a corporation shall not redeem its stock for cash or
property if such redemption would cause an impairment of capital of the
corporation. The DGCL further provides that a corporation may pay dividends (i)
out of its capital surplus or (ii) in the event there is no capital surplus, out
of its net profits for the fiscal year in which the dividend is declared and/or
the preceding year.

Fiduciary Duties of Directors

   Both Delaware and Pennsylvania law provide that a corporation's board of
directors has the ultimate responsibility for managing the business and affairs
of the corporation. The PBCL expressly provides that directors of a Pennsylvania
corporation are obligated to perform their duties in good faith, in a manner
they reasonably believe to be in the best interests of the corporation and with
such care, including reasonable inquiry, skill and diligence as a person of
ordinary prudence would use under similar circumstances. Absent breach of
fiduciary duty, lack of good faith or self-dealing, actions taken as a director
of a Pennsylvania corporation are presumed to be in the best interests of the
corporation. The PBCL states that directors of a Pennsylvania corporation may,
but are not required to, take into consideration the effects of their actions
upon various groups affected by such action, including not only shareholders,
but also employees, suppliers, customers, creditors and communities. The PBCL
also makes clear that a director has no greater obligation to justify, or higher
burden of proof with respect to, any act relating to an actual or potential
takeover of the corporation than he or she has with respect to any other act as
a director.

   The DGCL is silent as to the nature of the duties of directors of a Delaware
corporation. Delaware courts have held that the duty of care requires the
directors to exercise an informed business judgment. Under Delaware case law, an
informed business judgment means that the directors have informed themselves of
all material information reasonably available to them. Having become so
informed, they then must act with requisite care in the discharge of their
duties. Delaware courts have also imposed a heightened standard of scrutiny
regarding the conduct of directors in resisting unsolicited takeover attempts.
Liability of directors of a Delaware corporation to the corporation or its
stockholders for breach of the duty of care generally requires a finding by a
court that the directors were grossly negligent. Delaware courts have also held
that the directors of a Delaware corporation owe the corporation and its
stockholders a duty of loyalty, requiring them to act in good faith and in what
they believe to be the best interests of the corporation and its stockholders
and that, whenever their interests with respect to a transaction conflict with
those of the corporation, the transaction be fair to the corporation.

   The duty of loyalty in both states requires that the directors act in good
faith and place the best interests of the corporation and its stockholders above
any individual interests of their own.

Director and Officer Liability and Indemnification

   In accordance with the PBCL, Mylan's Bylaws provide that a director of Mylan
shall not be personally liable for monetary damages for any action taken, or any
failure to take any action, unless the director has breached or failed to
perform the duties required under Pennsylvania law and the breach or failure to
perform constitutes self-dealing, willful misconduct or recklessness.

                                       44
<PAGE>
 
   As permitted by the PBCL, Mylan's Bylaws provide that directors of Mylan are
indemnified under certain circumstances for expenses, judgments, fines or
settlements incurred in connection with suits and other legal proceedings. The
PBCL allows indemnification in cases where the person "acted in good faith and
in a manner he reasonably believed to be in, or not opposed to, the best
interests of the corporation and, with respect to any criminal proceeding, had
no reasonable cause to believe his conduct was unlawful."

   Under the DGCL, a corporation may include in its certificate of incorporation
provisions which eliminate or limit, within prescribed limitations, the personal
liability of a director of the corporation for monetary damages for breach of
fiduciary duty as a director. Penederm's Certificate limits the personal
liability of directors for monetary damages for breaches of their fiduciary duty
as directors to the fullest extent permissible under the DGCL.

   The DGCL generally provides that a corporation may, and in certain
circumstances must, indemnify its directors, officers, employees or agents
("indemnitees") for expenses (including attorneys' fees), judgments, fines or
settlements actually and reasonably incurred by them in connection with suits
and other legal actions or proceedings if they acted in good faith and in a
manner they reasonably believed to be in or not opposed to the best interests of
the corporation and, with respect to any criminal action or proceeding, had no
reasonable cause to believe their conduct was unlawful. In the case of
stockholder derivative suits, the corporation may indemnify its directors,
officers, employees or agents if they acted in good faith and in a manner they
reasonably believed to be in or not opposed to the best interests of the
corporation, except that no indemnification may be made in respect of any claim,
issue or matter as to which such person shall have been adjudged liable to the
corporation unless and only to the extent that the Court of Chancery or the
court in which the action was brought determined upon application that, in view
of all the circumstances of the case, the person is fairly and reasonably
entitled to indemnity for such expenses as the court deems proper. The DGCL also
permits a corporation to adopt procedures for advancing expenses to indemnitees
without the need for a case-by-case determination of eligibility, so long as in
the case of officers and directors they undertake to repay the amounts advanced
if it is ultimately determined that the officer or director was not entitled to
be indemnified.

   Penederm's Certificate requires indemnification of officers, directors,
employees and agents acting on behalf of Penederm to the fullest extent
permissible under the DGCL.

Charter Amendments

   Under the PBCL, amendments to a corporation's articles of incorporation may
only be proposed by its board of directors. Except for certain amendments which
do not require shareholder approval and unless a greater vote is required by its
articles of incorporation, amendments of the articles of incorporation of a
Pennsylvania corporation are to be approved by the affirmative vote of a
majority of the votes cast by all shareholders entitled to vote thereon and, if
any class or series of capital stock is entitled to vote as a class, the
affirmative vote of a majority of the votes cast in each such separate vote.

   To amend a Delaware corporation's certificate of incorporation, the DGCL
requires approval first by that corporation's board of directors and then by the
holders of a majority of the outstanding shares of stock entitled to vote
thereon and a majority of each class of stock entitled to vote thereon as a
class, unless a larger proportion is specified in its certificate of
incorporation or except when the provision being amended or repealed provides
for a supermajority vote of the board or the stockholders, in which case, the
same percentage of the board or the stockholders, as the case may be, is needed
to amend or repeal that provision.

Bylaw Amendments

   Under the PBCL, the shareholders of a Pennsylvania corporation who are
entitled to vote have the power to adopt, amend and repeal its bylaws. The
authority to adopt, amend and repeal bylaws of a Pennsylvania corporation may be
expressly vested by the bylaws in the board of directors, subject to the power
of the shareholders to override such actions and except that a board of
directors may not have the authority to adopt or change a bylaw on any subject
that is committed expressly to the shareholders under the PBCL, unless the
articles of incorporation of that corporation give the board that authority.

                                       45
<PAGE>
 
   Under the DGCL, the stockholders entitled to vote have the power to adopt,
amend or repeal bylaws as do the directors to the extent that the certificate of
incorporation confers such powers on the directors. Penederm's Certificate
expressly grants the Penederm Board the authority to adopt, amend or repeal
Penederm's Bylaws.

                        DESCRIPTION OF MYLAN CAPITAL STOCK

   The authorized capital stock of Mylan consists of 300,000,000 shares of Mylan
Common Stock, of which, as of the date of this Proxy Statement/Prospectus,
122,401,404 shares are outstanding, and 5,000,000 shares of preferred stock,
par value $.50 per share ("Mylan Preferred Stock"), issuable in series, none of
which are outstanding as of the date of this Proxy Statement/Prospectus.

Mylan Common Stock

   Holders of Mylan Common Stock have one vote per share on all matters
submitted to a vote of shareholders. Shareholders do not have cumulative voting
rights. The holders of Mylan Common Stock have the right to receive dividends
when, as and if declared by the Board of Directors of Mylan out of funds legally
available therefor, subject to the rights of the holders of any outstanding
Mylan Preferred Stock to receive preferential dividends. Upon the liquidation of
Mylan, holders of Mylan Common Stock would share ratably in any assets available
for distribution to shareholders after payment of all obligations of Mylan and
the aggregate liquidation preference (including accrued and unpaid dividends) of
any outstanding Mylan Preferred Stock.

   The Mylan Common Stock is not redeemable and has no preemptive, subscription
or conversion rights. Shares of Mylan Common Stock currently outstanding are,
and the Mylan Common Stock to be issued in the Merger will be, validly issued,
fully paid and nonassessable.

   American Stock Transfer Co., New York, New York, is the transfer agent and
registrar for the Mylan Common Stock.

Mylan Preferred Stock

   The authorized Mylan Preferred Stock is available for issuance from time to
time at the discretion of the Board of Directors of Mylan without shareholder
approval. The Board of Directors has authority to prescribe for each series of
Mylan Preferred Stock it establishes the number of shares in that series, the
dividend rate, and the voting rights, conversion privileges, redemption, sinking
fund and liquidation rights, if any, and any other rights, preferences,
qualifications and limitations of the particular series. The issuance of Mylan
Preferred Stock could decrease the amount of earnings and assets available for
distribution to the holders of Mylan Common Stock or adversely affect the rights
and powers, including voting rights, of the holders of Mylan Common Stock. Mylan
has no present plans to issue any Mylan Preferred Stock.

Special Considerations

   Mylan is subject to provisions of the PBCL regarding business combinations.
See "COMPARISON OF SHAREHOLDER RIGHTS--Shareholder Voting Rights."

   In addition, Mylan's Articles provide that each of the following corporate
actions requires approval in compliance with all applicable provisions of the
PBCL and Mylan's Articles and, with certain exceptions, the affirmative vote of
at least 75% of the outstanding shares of Mylan Common Stock entitled to vote,
at a meeting called for such purpose: (i) any merger or consolidation to which
Mylan and an Interested Person (as defined in Mylan's Articles) are parties;
(ii) any sale, lease, exchange or other disposition, in a single transaction or
series of related transactions, of all or substantially all or a Substantial
Part (as defined in Mylan's Articles) of the properties or assets of Mylan to an
Interested Person; (iii) the adoption of any plan or proposal for the
liquidation or dissolution of Mylan under or pursuant to which the rights or
benefits inuring to an Interested Person are different in kind or character from
the rights or benefits inuring to the other holders of Mylan Common Stock; (iv)
any transaction of the foregoing character involving an Affiliate or Associate
(as defined in Mylan's Articles) of an Interested Person or involving an
Associate of any such Affiliate. The 75% voting requirement will not apply if
the

                                       46
<PAGE>
 
Board of Directors shall have approved the transaction by a majority vote of all
directors prior to the time the Interested Person connected with the transaction
became an Interested Person or if the Board of Directors shall have approved the
transaction prior to consummation thereof by a majority vote of all directors,
disregarding the vote of each director who was an Interested Person, or an
Affiliate, Associate or agent of such Interested Person, or an Associate or
agent of any such Affiliate. The affirmative vote of the holders of at least 75%
of the outstanding shares of Mylan Common Stock entitled to vote is required to
amend or repeal the foregoing provisions.

   Mylan's Bylaws provide that a director shall not be personally liable for
monetary damages as such for any action, or any failure to take any action,
unless he has breached or failed to perform his statutory duties and the breach
or failure to perform constitutes self-dealing, willful misconduct or
recklessness; provided, however, that such limitation of liability shall not
apply to the responsibility or liability of a director pursuant to any criminal
statute or to liability for payment of taxes pursuant to local, state or federal
law. If Pennsylvania law is amended in the future to authorize corporate action
further limiting the personal liability of directors, the liability of a
director will be limited to the fullest extent permitted by such amendment.

              UNAUDITED PRO FORMA COMBINED FINANCIAL INFORMATION

   The following tables present the combination of Mylan and its subsidiaries
and Penederm and its subsidiary. The combination will be accounted for by Mylan
under the purchase method of accounting. The results of operations of Penederm
have been converted to a fiscal March 31 year-end and are unaudited.

   The Unaudited Pro Forma Combined Financial Statements reflect the significant
adjustments giving effect to the Merger (including the preliminary purchase
accounting adjustments) that are expected to have a continuing impact on Mylan.
Estimates relating to the fair value of Penederm's assets, liabilities and other
events requiring recognition have been made as more fully described in the Notes
to the Unaudited Pro Forma Combined Financial Statements. Actual adjustments
will be made on the basis of actual assets, liabilities and other items as of
the Effective Date on the basis of appraisals and evaluations, and therefore,
actual fair value amounts are expected to differ from those reflected in the
Unaudited Pro Forma Combined Financial Information.

   The pro forma financial information included herein does not purport to
represent what the consolidated financial position or results of operations
actually would have been if the Merger in fact had occurred on such dates or at
the beginning of the period indicated or to project the consolidated financial
position or results of operations as of any future date or any future period.

   The pro forma financial information included herein should be read in
conjunction with the historical consolidated financial statements of Mylan and
Penederm, including the notes thereto, and other financial information
incorporated by reference into this Proxy Statement/Prospectus. See
"INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE."


                                       47
<PAGE>
 
Mylan Laboratories Inc. and Subsidiaries
Pro Forma Combined Balance Sheet
As of June 30, 1998
(Amounts in thousands)
(Unaudited)

<TABLE>
<CAPTION>
                                                                                        Pro Forma                Pro Forma
                                                          Mylan      Penederm          Adjustments               Combined 
                                                        ---------    ---------         -----------               ---------  
<S>                                                     <C>          <C>               <C>                       <C>
Assets
Current assets:
 Cash and cash equivalents                               $139,111    $  1,732                  --                 $140,843
 Marketable securities                                     17,979       1,000                  --                   18,979
 Accounts receivable                                      137,229       7,280                  --                  144,509
 Inventories                                              150,032       2,385                  --                  152,417
 Deferred income tax benefit                                9,559          --                  --                    9,559
 Prepaid and refundable income tax                          7,890         382                  --                    8,272
 Other current assets                                       6,198          --                  --                    6,198
 In-process research and development                           --          --           $ 145,000   (1)                 --
                                                                                         (145,000)  (3)
                                                      -----------    ---------          ---------                 --------
Total current assets                                      467,998      12,779                  --                  480,777
Property, plant and equipment, net of accumulated         153,207         270                  --                  153,477
 depreciation
Marketable securities, non-current                         21,131          --                  --                   21,131
Intangible assets-net of accumulated amortization         126,855       1,720              67,000   (1)            199,158
                                                                                            3,583   (1)
Other assets                                               89,907          --                  --                   89,907
Investment in and advances to Somerset                     31,801          --                  --                   31,801
                                                      -----------    ---------          ---------                 --------
Total Assets                                             $890,899    $ 14,769           $  70,583                 $976,251
                                                      ===========    =========          =========                 ========

Liabilities and Shareholders' Equity
Current Liabilities:
 Trade accounts payable                                  $ 18,817    $  1,039                  --                 $ 19,856
 Current portion of long-term debt                          9,118          --                  --                    9,118
 Income taxes payable                                      18,376          --                  --                   18,376
 Other current liabilities                                 35,069       6,208           $   2,500   (1)             43,777
 Cash dividend payable                                      4,907          --                  --                    4,907
                                                      -----------    ---------          ---------                 --------
Total current liabilities                                  86,287       7,247               2,500                   96,034
Long-term debt                                              4,000          --                  --                    4,000
Long-term obligations                                      22,417           5                  --                   22,422
Deferred income tax liability                               3,490          --               6,100   (1)(2)           9,590
Shareholders' equity
 Preferred stock                                               --          --                  --                       --
 Common stock                                              61,609          86               2,950   (1)             64,559
                                                                                              (86)  (1)
 Additional paid-in capital                                94,778      61,111             211,550   (1)            306,328
                                                                                          (61,111)  (1)
 Retained earnings (deficit)                              624,134     (53,680)           (145,000)  (3)            479,134
                                                                                           53,680   (1)
 Unrealized gain on investments                                78          --                  --                       78
                                                      -----------    ---------          ---------                 --------
                                                          780,599       7,517              61,983                  850,099
Less:  Treasury stock                                       5,894          --                  --                    5,894
                                                      -----------    ---------          ---------                 --------
 
Net worth                                                 774,705       7,517              61,983                  844,205
                                                      -----------    ---------          ---------                 --------
Total liabilities and shareholders' equity               $890,899    $ 14,769           $  70,583                 $976,251
                                                      ===========    =========          =========                 ========
</TABLE>
See accompanying Notes to the Unaudited Pro Forma Combined Financial Statements.



                                      48
<PAGE>
 
Mylan Laboratories Inc. and Subsidiaries
Pro Forma Combined Income Statement
For the Year Ended March 31, 1998
(Amounts in thousands, except for per share data)
(Unaudited)

<TABLE>
<CAPTION>
                                                                                                    Pro Forma          Pro Forma
                                                                     Mylan       Penederm          Adjustments         Combined
                                                                   ---------    ----------         -----------         ---------
<S>                                                                <C>          <C>                <C>                 <C>
Revenues:                                                                                                           
 Net Sales                                                          $528,601     $  6,470                  --           $535,071
 Other                                                                26,822        3,635                  --             30,457
                                                                   ---------     ---------            --------          --------
Total Revenues                                                       555,423       10,105                  --            565,528
                                                                                                                    
Costs and Expenses:                                                                                                 
 Costs of Sales                                                      288,290        2,624             $ 3,350   (4)      294,264
 Research and Development                                             46,278        8,119                  --             54,397
 Selling, General and Administrative                                  96,708       12,381                 179  (4)      109,268
                                                                   ---------     ---------            --------          --------
Total Costs and Expenses                                             431,276       23,124               3,529            457,929
                                                                                                                    
Equity in Earnings of Somerset                                        10,282           --                  --             10,282
Other Income, net                                                     13,960          409                  --             14,369
                                                                   ---------     ---------            --------          --------
Income (Loss) Before Income Taxes                                    148,389      (12,610)             (3,529)           132,250
Income Taxes                                                          47,612           --              (1,340)  (5)       41,228
                                                                                                       (5,044)  (6) 
                                                                   ---------     ---------            --------          --------
Net Earnings (Loss)  (7)                                            $100,777     $(12,610)            $ 2,855           $ 91,022
                                                                   =========     =========            ========          ========
                                                                                                                    
Net Earnings (Loss) Per Common Share:  (7)                                                                          
  Basic                                                                $0.83       $(1.55)                                 $0.71
  Diluted                                                               0.82        (1.55)                                  0.71
                                                                                                                    
Shares Used in Net Earnings (Loss) Per Common Share
  Computation-Basic                                                  122,094        8,147              (2,607)           127,634
Shares Used in Net Earnings (Loss) Per Common Share
  Computation-Diluted                                                123,043        8,147              (2,529)           128,661
</TABLE>

See accompanying Notes to the Unaudited Pro Forma Combined Financial Statements.




                                      49
<PAGE>
 
Mylan Laboratories Inc. and Subsidiaries
Pro Forma Combined Income Statement
For the Three Months Ended June 30, 1998
(Amounts in thousands, except for per share data)
(Unaudited)

<TABLE>
<CAPTION>
                                                                                                   Pro Forma           Pro Forma
                                                                     Mylan      Penederm          Adjustments          Combined
                                                                   ---------    ---------         -----------          ---------
<S>                                                                <C>          <C>               <C>                  <C>
Revenues:                                                                                                           
 Net Sales                                                          $166,718     $ 4,388                  --            $171,106
 Other                                                                    --       1,936                  --               1,936
                                                                    --------     --------            --------           --------
Total Revenues                                                       166,718       6,324                  --             173,042
                                                                                                                    
Costs and Expenses:                                                                                                 
 Costs of Sales                                                       81,564       1,147             $   838   (4)        83,549
 Research and Development                                             14,084       1,134                  --              15,218
 Selling, General and Administrative                                  25,009       5,230                  45   (4)        29,384
                                                                                                        (900)  (7)  
                                                                    --------     --------            --------           --------
Total Costs and Expenses                                             120,657       7,511                 (17)            128,151
                                                                                                                    
Equity in Earnings of Somerset                                         2,350          --                  --               2,350
Other Income, net                                                      4,034          27                  --               4,061
                                                                    --------     --------            --------           --------
Income (Loss) Before Income Taxes                                     52,445      (1,160)                 17              51,302
Income Taxes                                                          18,263          --                (335)  (5)        17,464
                                                                                                        (464)  (6)  
                                                                    --------     --------            --------           --------
Net Earnings (Loss)  (7)                                            $ 34,182     $(1,160)            $   816            $ 33,838
                                                                    ========     ========            ========           ========
                                                                                                                    
Net Earnings (Loss) Per Common Share:  (7)                                                                                      
  Basic                                                                $0.28      $(0.14)                                  $0.26
  Diluted                                                               0.28       (0.14)                                   0.26
                                                                                                                    
Shares Used in Net Earnings (Loss) Per Common Share
  Computation-Basic                                                  122,295       8,511              (2,724)            128,082
Shares Used in Net Earnings (Loss) Per Common Share
  Computation-Diluted                                                124,078       8,511              (2,389)            130,200
</TABLE>

See accompanying Notes to the Unaudited Pro Forma Combined Financial Statements.



                                      50
<PAGE>
 
Mylan Laboratories Inc. and Subsidiaries
Notes to Pro Forma Combined Financial Statements
(Amounts in thousands, except per share data)

(1) Records the purchase accounting adjustments (pursuant to Accounting
    Principles Board Opinion No. 16) necessary to record Mylan's acquisition of
    Penederm's net assets for approximately $217,000. Intangible assets relate
    principally to existing product patents and trademarks. The allocation of
    the purchase price is subject to change based on final valuation and
    appraisals and was estimated as follows:

    Net worth of Penederm at June 30, 1998               $  7,517
    Intangible assets                                      67,000
    In-process research and development                   145,000
    Goodwill                                                3,583
    Net deferred tax liability                             (6,100)
                                                         --------
    Purchase price                                       $217,000
                                                         ========

    The estimated purchase price includes the issuance of approximately
    5,900,000 shares of Mylan Common Stock for Penederm Common Stock outstanding
    and includes the fair value of vested Penederm stock options assumed by
    Mylan and Mylan's direct acquisition costs estimated at $2,500.

(2) Record the deferred taxes related to the purchase.  Specifically, $20,700 in
    tax benefits associated with Penederm's net operating loss and credit
    carryforwards netted with deferred taxes provided on the $67,000 in
    intangibles assets (principally patents) acquired with no tax basis 
    (calculated as the $67,000 of intangible assets times the 40% tax rate
    which equals $26,800 of deferred tax liability less $20,700 in tax benefits
    acquired).

(3) Records the write-off of the in-process research and development upon
    consummation of the acquisition.

(4) Reflects the estimated amortization of intangibles (including goodwill)
    pursuant to the purchase method of accounting.  Intangibles are being
    amortized on a straight line basis over their economic useful life which is
    estimated to be 20 years.  The allocation of the purchase price and the
    useful life assigned are subject to change based on the final valuation and
    appraisals.  The in-process research and development will be charged to
    research and development expense upon consummation of the Merger but is not
    included in the Unaudited Pro Forma Combined Income Statements as it is
    nonrecurring in nature.

                                               Useful Life             Annual
                               Allocation        (Years)            Amortization
 
    Patents and Trademarks     $67,000               20             $    3,350
    Goodwill                     3,583               20                    179
                                                                    ----------
                                                                    $    3,529
                                                                    ==========

(5) Reflects the tax effect of the amortization of patents and trademarks
    assuming a 40% taxable rate.

      Yearly amortization of intangibles     Taxable Rate         Annual Benefit
                                             ------------         --------------
                                  $3,350         40%              $        1,340

(6) To recognize tax benefit associated with Penederm's current year loss using
    a 40% effective tax rate.

(7) As required by Article 11 of Regulation S-X under the Securities Exchange
    Act of 1934, the pro forma income statements exclude the nonrecurring charge
    for in-process research and development estimated at $145,000 and $900 of
    nonrecurring acquisition costs incurred by Penederm during the three months
    ended June 30, 1998.  The following schedule shows the effect of the write-
    off (had it occurred as of the first day of each period presented) on Pro
    Forma Net (Loss) and Pro Forma Net (Loss) Per Common Share-Basic and
    Diluted.

 
                                        Three Months
                                           Ended                    Year Ended
                                        June 30, 1998             March 31, 1998

    Net (Loss)                          $   (112,062)                $  (53,978)
                                       ==============               ============
    Per Common Share
    Net (Loss)-Basic and Diluted        $      (0.87)                $    (0.42)
                                       ==============               ============

Note:  There are no eliminations of intercompany accounts and balances between
Mylan and Penederm as amounts are immaterial.



                                      51
<PAGE>
 
                                     EXPERTS

   The consolidated financial statements of Mylan at March 31, 1998 and 1997 and
for each of the three years in the period ended March 31, 1998, incorporated in
this Proxy Statement/Prospectus by reference from Mylan's 1998 Form 10-K, have
been audited by Deloitte & Touche LLP, independent auditors, as stated in their
report which is incorporated by reference herein, and have been so incorporated
in reliance upon the report of such firm given upon their authority as experts
in accounting and auditing.

   The consolidated financial statements of Somerset Pharmaceuticals, Inc. at
December 31, 1997 and 1996 and for each of the three years in the period ended
December 31, 1997, incorporated in this Proxy Statement/Prospectus by reference
from Mylan's 1998 Form 10-K, have been audited by Deloitte & Touche LLP,
independent auditors, as stated in their report which is incorporated by
reference herein, and have been so incorporated in reliance upon the report of
such firm given upon their authority as experts in accounting and auditing.

   The consolidated financial statements of Penederm as of December 31, 1997 and
1996, and for each of the three years in the period ended December 31, 1997,
have been incorporated in this Proxy Statement/Prospectus by reference from
Penederm's 1997 Form 10-K, have been audited by Ernst & Young LLP, independent
auditors, as stated in their report which is incorporated by reference herein,
and have been so incorporated in reliance upon the report of such firm given
upon their authority as experts in accounting and auditing.

                                  LEGAL MATTERS

   The validity of the Mylan Common Stock to be issued by Mylan in connection
with the Merger will be passed upon by Buchanan Ingersoll Professional
Corporation, Pittsburgh, Pennsylvania.

   Certain tax matters relating to the Merger will be passed upon for Penederm
by Heller Ehrman White & McAuliffe, Palo Alto, California, and for Mylan by
Buchanan Ingersoll Professional Corporation, Pittsburgh, Pennsylvania.

                              STOCKHOLDER PROPOSALS

   Penederm will hold a 1999 Annual Meeting of Stockholders only if the Merger
is not consummated. In the event that such a meeting is held, any proposal of a
Penederm Stockholder intended to be presented at the 1999 Annual Meeting will be
required to be received by the Secretary of Penederm no later than January 11,
1999 in order to be considered for inclusion in the Penederm 1999 proxy
materials. Any such proposal will be subject to Rule 14a-8 of the Rules and
Regulations under the Exchange Act.

                                       52
<PAGE>

                                  APPENDIX A

 
                          AGREEMENT AND PLAN OF MERGER

                                  BY AND AMONG

                             PENEDERM INCORPORATED

                                      AND

                             MLI ACQUISITION CORP.

                                      AND

                            MYLAN LABORATORIES INC.

                                 June 24, 1998



<PAGE>
 
                               TABLE OF CONTENTS



<TABLE> 
<CAPTION> 
                                                                                                               Page
                                                                                                               ----
<S>      <C> 
1.       NAME OF SURVIVING CORPORATION, CERTIFICATE OF INCORPORATION, BYLAWS......................................2
         1.1      Name of Surviving Corporation...................................................................2
         1.2      Certificate of Incorporation....................................................................2
         1.3      Bylaws; Directors and Officers..................................................................2
         1.4      Filing of Certificate of Merger; Effective Date; Effective Time.................................3
         1.5      Effects of Merger...............................................................................3
         1.6      Tax-Free Reorganization.........................................................................3

2.       STATUS AND CONVERSION OF SECURITIES......................................................................3
         2.1      Company Capital Stock...........................................................................3
                  (a)      Conversion of Company Common Stock Into Parent Common Stock............................3
                  (b)      Delivery of Certificates...............................................................4
                  (c)      Dividends; Transfer Taxes; Withholding.................................................5
                  (d)      No Fractional Shares...................................................................6
                  (e)      Return of Exchange Fund................................................................6
                  (f)      Adjustment of Exchange Ratio...........................................................7
                  (g)      No Further Ownership Rights in Company Common Stock....................................7
                  (h)      Closing of the Company Transfer Books..................................................7
                  (i)      Further Assurances.....................................................................7
         2.2      Subsidiary Common Stock.........................................................................8
         2.3      Assumption of Stock Options; Company Warrant; Employee Stock Purchase Plan......................8
         2.4      Closing.........................................................................................9

3.       REPRESENTATIONS, WARRANTIES AND AGREEMENTS...............................................................9
         3.1      Representations, Warranties and Agreements of the Company.......................................9
                  (a)      Organization, Standing and Power......................................................10
                  (b)      Capital Structure.....................................................................10
                  (c)      Authority.............................................................................12
                  (d)      Consents and Approvals; No Violation..................................................13
                  (e)      SEC Documents and Other Reports.......................................................14
                  (f)      Registration Statement and Prospectus/Proxy Statement.................................15
                  (g)      Absence of Certain Changes or Events..................................................15
                  (h)      Permits and Compliance................................................................16
                  (i)      Tax Matters...........................................................................17
                  (j)      Actions and Proceedings...............................................................18
                  (k)      FDA and Related Matters...............................................................19
                  (l)      Certain Agreements....................................................................20
                  (m)      Material Contracts....................................................................21
                  (n)      Opinion of Financial Advisor..........................................................21
                  (o)      Takeover Provisions Inapplicable......................................................21
                  (p)      Required Vote of the Company Stockholders.............................................21
                  (q)      Finders and Investment Bankers........................................................22
                  (r)      Authorized Stock......................................................................22
</TABLE> 
                                     - i -
<PAGE>
 
<TABLE> 
<S>      <C> 
                  (s)      Company Affiliates....................................................................22
                  (t)      Owned Real Property...................................................................22
                  (u)      Leased Real Estate....................................................................22
                  (v)      Owned and Leased Tangible Personal Property...........................................23
                  (w)      Physical Condition of Property........................................................23
                  (x)      Patents and Certain Other Intellectual Property Rights................................23
                  (y)      Accounts Receivable...................................................................24
                  (z)      Insurance and Bonds...................................................................24
                  (aa)     Product Warranties and Liability......................................................24
                  (bb)     Contracts, Proposals and Bids.........................................................25
                  (cc)     Labor and Employment Matters..........................................................25
                  (dd)     Insider Contracts.....................................................................27
                  (ee)     Other Material Contracts..............................................................27
                  (ff)     Export of Products and Technologies...................................................28
                  (gg)     Absence of Illegal Payments...........................................................28
                  (hh)     Absence of Anti-Boycott Violations....................................................29
                  (ii)     Environmental Matters.................................................................29
                  (jj)     No Adverse Actions....................................................................31
         3.2      Representations, Warranties and Agreements of the Parent.......................................31
                  (a)      Organization, Standing and Power......................................................31
                  (b)      Capital Structure.....................................................................32
                  (c)      Authority.............................................................................33
                  (d)      Consents and Approvals; No Violation..................................................34
                  (e)      SEC Documents and Other Reports.......................................................35
                  (f)      Registration Statement and Prospectus/Proxy Statement.................................36
                  (g)      Absence of Certain Changes or Events..................................................36
                  (h)      Permits and Compliance................................................................36
                  (i)      Actions and Proceedings...............................................................37
                  (j)      FDA Matters...........................................................................38
                  (k)      Labor Relations.......................................................................39
                  (l)      Patents and Certain Other Intellectual Property Rights................................39
                  (m)      Parent Common Stock...................................................................39
                  (n)      Opinion of Financial Advisor..........................................................39
                  (o)      Finders and Investment Bankers........................................................40
                  (p)      Parent Affiliate Agreements...........................................................40
         3.3      Representations and Warranties as to the Merger Subsidiary.....................................40
                  (a)      Organization, Standing, Power and Capitalization of the Merger Subsidiary.............40
                  (b)      Business of the Merger Subsidiary.....................................................40
                  (c)      Authorization; Binding Agreement......................................................40
                  (d)      Compliance With Other Instruments, Etc................................................41
                  (e)      Governmental and Other Consents, Etc..................................................41

4.       COVENANTS...............................................................................................41
         4.1      Covenants of the Company.......................................................................41
                  (a)      Action in Furtherance of Merger.......................................................41
                  (b)      Maintenance of Properties.............................................................42
</TABLE> 
                                    - ii -
<PAGE>
 
<TABLE> 
<S>      <C> 
                  (c)      Access and Information................................................................42
                  (d)      Conduct of Business...................................................................43
                  (e)      Capital Stock.........................................................................44
                  (f)      No Solicitation.......................................................................45
                  (g)      No Final Put Notice...................................................................47
                  (h)      Compensation Matters..................................................................47
                  (i)      Contracts.............................................................................47
                  (j)      Tax Matters...........................................................................47
                  (k)      Amendments to the Schedules...........................................................47
                  (l)      Notification of Certain Matters.......................................................48
                  (m)      Stockholder Approval..................................................................48
                  (n)      Financial Statements..................................................................49
                  (o)      Proxy Statement.......................................................................49
                  (p)      Company Affiliates....................................................................49
                  (q)      Takeover Statutes.....................................................................49
                  (r)      Prohibited Transactions...............................................................49
                  (s)      Accounting Changes....................................................................50
                  (t)      Compliance With Law...................................................................50
                  (u)      Company Affiliates Agreements.........................................................50
         4.2      Covenants of the Parent........................................................................50
                  (a)      Action in Furtherance of Merger.......................................................50
                  (b)      Maintenance of Properties.............................................................51
                  (c)      Access and Information................................................................51
                  (d)      Listing Application...................................................................51
                  (e)      Public Filings........................................................................51
                  (f)      Registration Statement................................................................51
                  (g)      Conduct of Business...................................................................51
         4.3      Covenants as to the Merger Subsidiary..........................................................52
                  (a)      No Business...........................................................................52
                  (b)      Access................................................................................52
                  (c)      Actions in Furtherance of Merger......................................................52
         4.4      Covenants of the Company and the Parent........................................................52
                  (a)      Registration Statement................................................................52
                  (b)      Tax-Free Reorganization Treatment.....................................................52

5.       CONDITIONS TO CLOSING; ABANDONMENT AND TERMINATION......................................................53
         5.1      Conditions to Each Party's Obligation to Effect the Merger.....................................53
                  (a)      Company Stockholder Approval..........................................................53
                  (b)      Consents..............................................................................53
                  (c)      Effectiveness.........................................................................53
                  (d)      Listing...............................................................................53
                  (e)      No Legal Restraints...................................................................53
         5.2      Conditions to the Company's Closing and Its Right to Abandon...................................53
                  (a)      No Material Adverse Effect............................................................54
                  (b)      No Material Adverse Change............................................................54
                  (c)      Officer's Certificate.................................................................54
                  (d)      Tax Opinion...........................................................................54
</TABLE> 
                                    - iii -
<PAGE>
 
<TABLE> 
<S>      <C> 
                  (e)      Tax Certificate.......................................................................55
         5.3      Conditions to the Parent's and the Merger Subsidiary's Closing and Right of the Parent
                  and the Merger Subsidiary to Abandon...........................................................56
                  (a)      No Material Adverse Effect............................................................56
                  (b)      No Material Adverse Change............................................................57
                  (c)      Officer's Certificate.................................................................57
                  (d)      Tax Opinion...........................................................................57
                  (e)      Tax Certificates......................................................................58
                  (f)      Outstanding Shares of Preferred Stock.................................................58
                  (g)      FIRPTA Statement......................................................................58

6.       ADDITIONAL PROVISIONS FOR ABANDONMENT AND TERMINATION...................................................58
         6.1      Provisions of Abandonment and Termination......................................................58
                  (a)      Mutual Agreement......................................................................59
                  (b)      Violation of Order....................................................................59
                  (c)      Other Transactions Involving Company..................................................59
                  (d)      Superior Proposal.....................................................................60
         6.2      Termination of Agreement.......................................................................61
         6.3      Effect of Abandonment or Termination...........................................................61

7.       EXPENSES................................................................................................61
         7.1      Costs and Expenses.............................................................................61
                  (a)      Payment of Own Expenses...............................................................61
                  (b)      Termination Fee.......................................................................61

8.       MISCELLANEOUS...........................................................................................63
         8.1      Certification of the Company's Shareholder Votes, Etc..........................................63
         8.2      Certification of the Parent's Stockholder Votes, Etc...........................................63
         8.3      Termination of Covenants, Representations and Warranties.......................................63
         8.4      Certain Tax Matters............................................................................63
         8.5      Execution in Counterparts......................................................................67
         8.6      Waivers and Amendments.........................................................................67
         8.7      Confidentiality................................................................................67
         8.8      Indemnification; Directors and Officers Insurance..............................................67
         8.9      Notices........................................................................................68
         8.10     Entire Agreement; No Third-Party Beneficiaries; Rights of Ownership............................69
         8.11     Governing Law..................................................................................69
         8.12     Partial Invalidity.............................................................................69
         8.13     Publicity......................................................................................69
         8.14     Defined Terms..................................................................................69
         8.15     Benefit Plans..................................................................................70
         8.16     Enforcement of Agreement.......................................................................70
         8.17     Waiver of Jury Trial...........................................................................70
         8.18     No Presumption Against the Draftsman...........................................................71
</TABLE> 
APPENDIX A  GLOSSARY OF DEFINED TERMS/SECTION REFERENCES
 
                                    - iv -
<PAGE>
 
                                LIST OF EXHIBITS
                                ----------------
EXHIBIT
EXHIBIT A          COMPANY OPTION AGREEMENT                   Recital 7
EXHIBIT B-1        FORM OF VOTING AGREEMENT                   Recital 8
EXHIBIT B-2        FORM OF ALTERNATE VOTING AGREEMENT         Recital 8
EXHIBIT C          FORM OF COMPANY AFFILIATE AGREEMENT        4.1(p), 4.1(u),
                                                              4.4(c)(i), 3.1(t)
                                     - v -
<PAGE>
 
                          AGREEMENT AND PLAN OF MERGER

     THIS AGREEMENT AND PLAN OF MERGER (this "Agreement") is dated June 24,
1998, by and among PENEDERM INCORPORATED, a Delaware corporation (hereinafter
called the "Company"), and MLI ACQUISITION CORP., a Delaware corporation
(hereinafter called the "Merger Subsidiary") (the Company and the Merger
Subsidiary being hereinafter sometimes called the "Constituent Corporations"),
and MYLAN LABORATORIES INC., a Pennsylvania corporation (hereinafter called the
"Parent"), which is joining as a third party and is not a Constituent
Corporation.

RECITALS:

     1.     The Boards of Directors of each of the Parent and the Merger
Subsidiary have determined that it is in the best interests of the Parent and
the Merger Subsidiary and the Board of Directors of the Company has determined
that it is advisable and in the best interests of the Company and is fair to the
stockholders of the Company, for the Parent to acquire the Company upon the
terms and subject to the conditions set forth herein;

     2.     In furtherance of such acquisition, the Boards of Directors of the
Company and the Merger Subsidiary have resolved and approved that the Merger
Subsidiary be merged with and into the Company under and pursuant to the
Delaware General Corporation Law (the "DGCL") into a single corporation (the
"Merger") existing under the laws of the State of Delaware, and the Company
shall be the surviving corporation in the Merger (the Company in its capacity as
such surviving corporation being sometimes referred to herein as the "Surviving
Corporation");

     3.     The Parent, as sole shareholder of the Merger Subsidiary, and the
respective Boards of Directors of each of the Constituent Corporations and the
Parent have approved the Merger upon the terms and conditions hereinafter set
forth and have approved this Agreement;

     4.     The Merger is permitted pursuant to the DGCL;

     5.     For federal income tax purposes, it is intended that the Merger
shall qualify as a reorganization within the meaning of Section 368(a) of the
Internal Revenue Code of 1986, as amended (the "Code");

     6.     For accounting purposes, it is intended that the Merger shall be
accounted for under the purchase method;

     7.     Simultaneously with the execution and delivery of this Agreement and
as a condition and inducement to the Parent's and the Merger Subsidiary's
willingness to enter into this Agreement, the Parent is entering into a Stock
Option Agreement dated the date hereof in the form of Exhibit A (the "Company
                                                      ---------              
Option Agreement") with the Company pursuant to which the Company is granting to
the Parent the right and option to purchase 1,717,878 shares of common 

                                      A-1
<PAGE>
 
stock, par value $.01 per share, of the Company (the "Company Common Stock")
from the Company; and

     8.     Simultaneously with the execution and delivery of this Agreement and
as a condition and inducement to the Parent's and the Merger Subsidiary's
willingness to enter into this Agreement, the Parent is entering into Voting
Agreements in the form of Exhibit B-1 with certain members of the Board of
                          -----------                                     
Directors of the Company in their respective capacities as stockholders of the
Company and a Voting Agreement in the form of Exhibit B-2 with a member of the
                                              -----------                     
Board of Directors of the Company in his capacity as the general partner of a
limited partnership which is a stockholder of the Company (together, the "Voting
Agreements").

     NOW, THEREFORE, in consideration of the premises and the mutual agreements,
provisions and covenants herein contained and for other good and valuable
consideration, the receipt and adequacy of which are hereby acknowledged, the
parties hereto, intending to be legally bound, hereby agree that the Merger
Subsidiary shall be merged with and into the Company at the Effective Time in
accordance with the DGCL, the Company shall be the Surviving Corporation, and
the parties hereto adopt and agree to the following agreements, terms and
conditions relating to the Merger and the mode of carrying the same into effect.

1.          NAME OF SURVIVING CORPORATION, CERTIFICATE OF INCORPORATION, BYLAWS.
            ------------------------------------------------------------------- 
1.1         Name of Surviving Corporation.
            ----------------------------- 
          The name of the Surviving Corporation from and after the Effective
          Time shall be Penederm Incorporated.

1.2         Certificate of Incorporation.
            ---------------------------- 

          The Certificate of Incorporation of the Company as in effect on the
          date hereof shall from and after the Effective Time be and continue to
          be the Certificate of Incorporation of the Surviving Corporation until
          changed or amended as provided by law, except that at the Effective
          Time and upon filing of the Certificate of Merger, the Certificate of
          Incorporation of the Company shall be amended and restated in its
          entirety to read identically with the Certificate of Incorporation of
          the Merger Subsidiary except that the name of the Surviving
          Corporation shall be "Penederm Incorporated" (the "Amended and
          Restated Certificate of Incorporation").

1.3         Bylaws; Directors and Officers.
            ------------------------------ 

          The Bylaws of the Company as in effect immediately prior to the
          Effective Time shall from and after the Effective Time be and continue
          to be the Bylaws of the Surviving Corporation until amended as
          provided therein.  The directors and officers of the Merger Subsidiary
          at the Effective Time shall, from and after the 

                                      A-2
<PAGE>
 
          effectiveness of the Merger, be the directors and officers,
          respectively, of the Surviving Corporation until their successors
          shall have been duly elected or appointed and qualified or until their
          earlier death, resignation or removal in accordance with the Surviving
          Corporation's Amended and Restated Certificate of Incorporation and
          Bylaws.

1.4         Filing of Certificate of Merger; Effective Date; Effective Time.
            --------------------------------------------------------------- 

          Upon fulfillment of the conditions set forth in Article 5 hereof (or
          at such time thereafter as provided in the Certificate of Merger), and
          if this Agreement is not thereafter, and has not theretofore been,
          terminated or abandoned as permitted by the provisions hereof, then a
          Certificate of Merger shall be filed in accordance with Section 103
          and Section 251 of the DGCL.  Said Certificate of Merger shall be
          submitted for filing in accordance with the DGCL as soon as
          practicable after the Closing.  The Merger shall become effective
          immediately upon such filing with the Secretary of State of the State
          of Delaware, which time is herein referred to as the "Effective Time"
          and which date is herein referred to as the "Effective Date."

1.5         Effects of Merger.
            ----------------- 
          The Merger shall have the effects set forth in Section 259 of the
          DGCL.

1.6         Tax-Free Reorganization.
            ----------------------- 

          The Merger is intended to be a reorganization within the meaning of
          Section 368(a) of the Code, and this Agreement is intended to be a
          "plan of reorganization" within the meaning of the regulations
          promulgated under Section 368 of the Code.

2.          STATUS AND CONVERSION OF SECURITIES.
            ----------------------------------- 

     The manner and basis of converting the shares of the capital stock of the
     Constituent Corporations in the Merger and the nature and amount of
     securities of the Parent which the holders of shares of Company Common
     Stock are to receive in exchange for such shares in the Merger are as
     follows:

2.1         Company Capital Stock.
            --------------------- 

(a)         Conversion of Company Common Stock Into Parent Common Stock.  At
the Effective Time, the shares of Company Common Stock, other than Company
Common Stock (if any) owned by the Company, the Parent or the Merger Subsidiary,
shall, by virtue of the Merger and without any action on the part of the Parent,
the Merger Subsidiary, the Company, the Surviving Corporation or the holder
thereof, automatically be cancelled

                                      A-3

<PAGE>
 
and be converted into shares of common stock, par value $.50 per share, of the
Parent (the "Parent Common Stock") at a ratio equal to 0.68 shares of Parent
Common Stock for each share of Company Common Stock (the "Exchange Ratio"),
subject to the provisions of Sections 2.1(b) and 2.1(d). Any shares of Company
Common Stock (if any) owned by the Company, the Parent or the Merger Subsidiary
shall be cancelled and no Parent Common Stock or other consideration shall be
delivered in exchange therefor.

(b)  Delivery of Certificates.

     (i)  The Parent shall authorize American Stock Transfer and Trust Company 
          (or such other Person or Persons as shall be reasonably acceptable to
          the Parent and the Company) to act as Exchange Agent hereunder (the
          "Exchange Agent"). As soon as practicable after the Effective Time,
          the Parent shall deposit with the Exchange Agent, in trust for the
          holders of shares of Company Common Stock converted in the Merger,
          certificates representing the shares of Parent Common Stock issuable
          pursuant to Section 2.1(a) in exchange for outstanding shares of
          Company Common Stock and cash as required to make payments in lieu of
          any fractional shares pursuant to Section 2.1(d) (such cash and shares
          of Parent Common Stock, together with any dividends or distributions
          with respect thereto, being hereinafter referred to as the "Exchange
          Fund"). The Exchange Agent shall deliver the Parent Common Stock
          contemplated to be issued pursuant to Section 2.1(a) out of the
          Exchange Fund.

    (ii)  The Parent shall instruct the Exchange Agent, as soon as practicable 
          after the Effective Time, to mail to each record holder of a
          certificate or certificates which immediately prior to the Effective
          Time represented outstanding shares of Company Common Stock converted
          in the Merger (the "Certificates") a letter of transmittal (which
          shall specify that delivery shall be effected, and risk of loss and
          title to the Certificates shall pass, only upon actual delivery of the
          Certificates to the Exchange Agent, and shall contain instructions for
          use in effecting the surrender of the Certificates in exchange for
          certificates representing shares of Parent Common Stock and cash in
          lieu of fractional shares in accordance with Section 2.1(d)). Upon
          surrender for cancellation to the Exchange Agent of all Certificates
          held by any record holder of a Certificate, together with such letter
          of transmittal, duly executed, the holder of such Certificate shall be
          entitled to receive in exchange therefor a certificate representing
          that number of whole shares of Parent Common Stock into which the
          shares 

                                      A-4
<PAGE>
 
          represented by the surrendered Certificate shall have been converted
          at the Effective Time pursuant to this Article 2, cash in lieu of any
          fractional share in accordance with Section 2.1(d) and certain
          dividends and other distributions in accordance with Section 2.1(c),
          and any Certificate so surrendered shall forthwith be cancelled.

(c)  Dividends; Transfer Taxes; Withholding.  No dividends or other
distributions that are declared on or after the Effective Time on Parent Common
Stock, or are payable to the holders of record thereof on or after the Effective
Time, shall be paid to any Person entitled by reason of the Merger to receive a
certificate representing Parent Common Stock until such Person surrenders the
related Certificate or Certificates, as provided in Section 2.1(b), and no cash
payment in lieu of fractional shares shall be paid to any such Person pursuant
to Section 2.1(d) until such Person shall so surrender the related Certificate
or Certificates.  Subject to the effect of applicable law, there shall be paid
to each record holder of a new certificate representing such Parent Common
Stock:  (A) at the time of such surrender or as promptly as practicable
thereafter, the amount of any dividends or other distributions theretofore paid
with respect to the shares of Parent Common Stock represented by such new
certificate and having a record date on or after the Effective Time and a
payment date prior to such surrender; (B) at the appropriate payment date or as
promptly as practicable thereafter, the amount of any dividends or other
distributions payable with respect to such shares of Parent Common Stock and
having a record date on or after the Effective Time but prior to such surrender
and a payment date on or subsequent to such surrender; and (C) at the time of
such surrender or as promptly as practicable thereafter, the amount of any cash
payable with respect to a fractional share of Parent Common Stock to which such
holder is entitled pursuant to Section 2.1(d).  In no event shall the Person
entitled to receive any such dividends or other distributions be entitled to
receive interest on such dividends or other distributions.  If any cash or
certificate representing shares of Parent Common Stock is to be paid to or
issued in a name other than that in which the Certificate surrendered in
exchange therefor is registered, it shall be a condition of such exchange that
the Certificate so surrendered shall be properly endorsed and otherwise in
proper form for transfer and that the Person requesting such exchange shall pay
to the Exchange Agent any transfer or other taxes required by reason of the
issuance of certificates for such shares of Parent Common Stock in a name other
than that of the registered holder of the Certificate surrendered, or shall
establish to the satisfaction of the Exchange Agent that such tax has been paid
or is not applicable.  The Parent or the Exchange Agent shall be entitled to
deduct and withhold from the consideration otherwise payable pursuant to this
Agreement to any holder of shares of Company Common Stock such amounts as the

                                      A-5
<PAGE>
 
Parent or the Exchange Agent is required to deduct and withhold with respect to
the making of such payment under the Code or under any provision of state, local
or foreign tax law.  To the extent that amounts are so withheld by the Parent or
the Exchange Agent, such withheld amounts shall be treated for all purposes of
this Agreement as having been paid to the holder of the shares of Company Common
Stock in respect of which such deduction and withholding was made by the Parent
or the Exchange Agent.

(d)  No Fractional Shares.  No certificates or scrip representing
fractional shares of Parent Common Stock shall be issuable upon the surrender
for exchange of Certificates pursuant to this Article 2, and no dividend or
other distribution or stock split of the Parent shall relate to any fractional
share, and no fractional share shall entitle the owner thereof to vote or to any
other rights of a security holder of the Parent.  In lieu of any such fractional
share, each holder of Company Common Stock who would otherwise have been
entitled to a fraction of a share of Parent Common Stock upon surrender of
Certificates for exchange pursuant to this Article 2 shall be paid an amount in
cash (without interest), rounded to the nearest cent, determined by multiplying
(i) the per-share closing price on the New York Stock Exchange, Inc. (the
"NYSE") of Parent Common Stock (as reported in the NYSE Composite Transactions)
on the Effective Date (or, if the shares of Parent Common Stock do not trade on
the NYSE on such date, the first date of trading of shares of Parent Common
Stock on the NYSE after the Effective Time) by (ii) the fractional interest to
which such holder would otherwise be entitled.  As promptly as practicable after
the determination of the amount of cash, if any, to be paid to holders of
fractional share interests, the Exchange Agent shall so notify the Parent, and
the Parent shall deposit such amount with the Exchange Agent and shall cause the
Exchange Agent to forward payments to such holders of fractional share interests
subject to and in accordance with the terms of Section 2.1(c) and this Section
2.1(d).

(e)  Return of Exchange Fund.  Any portion of the Exchange Fund which
remains undistributed to the former stockholders of the Company for twelve (12)
months after the Effective Time shall be delivered to the Parent, upon demand of
the Parent, and any such former stockholders who have not theretofore complied
with this Article 2 shall thereafter look only to the Parent for payment of
their claims for Parent Common Stock, any cash in lieu of fractional shares of
Parent Common Stock and any dividends or distributions with respect to Parent
Common Stock.  Neither the Parent nor the Surviving Corporation shall be liable
to any former holder of Company Common Stock for any such shares of Parent
Common Stock, cash and dividends and distributions held in the Exchange

                                      A-6
<PAGE>
 
Fund which are delivered to a public official pursuant to any applicable
abandoned property, escheat or similar law.

(f)  Adjustment of Exchange Ratio.  In the event of any
reclassification, stock split, stock dividend, or other subdivision or
combination, with respect to the Parent Common Stock, any change or conversion
of Parent Common Stock into other securities of the Parent or any other dividend
or distribution with respect to the Parent Common Stock other than normal
quarterly cash dividends as the same may be adjusted from time to time pursuant
to the terms of this Agreement (or if a record date with respect to any of the
foregoing should occur) prior to the Effective Time, appropriate and
proportionate adjustments, if any, shall be made to the Exchange Ratio, and all
references to the Exchange Ratio in this Agreement shall be deemed to be to the
Exchange Ratio as so adjusted.

(g)  No Further Ownership Rights in Company Common Stock.  All shares
of Parent Common Stock issued upon the surrender for exchange of Certificates in
accordance with the terms hereof (including any cash paid pursuant to Section
2.1(d)) shall be deemed to have been issued in full satisfaction of all rights
pertaining to the shares of Company Common Stock represented by such
Certificates.

(h)  Closing of the Company Transfer Books.  At the Effective Time, the
stock transfer books of the Company shall be closed and no transfer of shares of
Company Common Stock shall thereafter be made on the records of the Company.
If, after the Effective Time, Certificates are presented to the Surviving
Corporation, the Exchange Agent or the Parent, such Certificates shall be
cancelled and exchanged as provided in this Article 2.

(i)  Further Assurances.  If at any time after the Effective Time the
Surviving Corporation shall consider or be advised that any deeds, bills of
sale, assignments or assurances or any other acts or things are necessary,
desirable or proper (a) to vest, perfect or confirm, of record or otherwise, in
the Surviving Corporation its right, title or interest in, to or under any of
the rights, privileges, powers, franchises, properties or assets of either of
the Constituent Corporations, or (b) otherwise to carry out the purposes of this
Agreement, the Surviving Corporation and its proper officers and directors or
their designees shall be authorized to execute and deliver, in the name and on
behalf of either of the Constituent Corporations, all such deeds, bills of sale,
assignments and assurances and to do, in the name and on behalf of either
Constituent Corporation, all such other acts and things as may be necessary,
desirable or proper to vest, perfect or confirm the Surviving Corporation's
right, title or interest in, to or under any of the rights, privileges, powers,
franchises, properties or assets of such

                                      A-7
<PAGE>
 
Constituent Corporation and otherwise to carry out the purposes of this
Agreement.

2.2         Subsidiary Common Stock.
            ----------------------- 

          Each share of  common stock, par value $.50 per share, of the Merger
          Subsidiary (the "Subsidiary Common Stock") outstanding immediately
          prior to the Effective Time shall, by virtue of the Merger and without
          any action on the part of the holder thereof, be converted into and be
          one share of the Common Stock of the Surviving Corporation.

2.3         Assumption of Stock Options; Company Warrant; Employee Stock
            ------------------------------------------------------------
            Purchase Plan.
            ------------- 

(a)  Except as expressly provided in this Section 2.3, all rights under any
     stock option granted by the Company pursuant to its Equity Incentive Plan,
     Employee Stock Option Plan, Consultant Stock Option Plan or Nonemployee
     Directors Stock Option Plan (collectively, the "Company Stock Option
     Plans") that remains unexercised immediately prior to the Effective Time
     ("Unexercised Options") shall, together with the Company Stock Option
     Plans, be assumed by the Parent, but shall thereafter represent the right
     to acquire that number of shares of Parent Common Stock to which the
     optionee would have been entitled pursuant to the Exchange Ratio if,
     immediately prior to the Effective Time, the optionee had fully exercised
     the option and had been a stockholder of record of the Company.  The option
     price per share of Parent Common Stock shall be equal to the exercise price
     per share of the Company Common Stock under each option divided by the
     Exchange Ratio, rounded up to the nearest cent.  The Parent and the Company
     shall each take all action necessary to assure that the rights and benefits
     of the optionee under each such option shall not be increased or decreased
     by reason of this Section 2.3, and in addition, each option which is an
     incentive stock option shall be adjusted as required by Section 424 of the
     Code and the regulations promulgated thereunder so as not to constitute a
     modification, extension or renewal of the option within the meaning of
     Section 424(h) of the Code.  The duration and other terms of the options
     shall be the same as the original Company options, except that reference to
     the Company in the Company Stock Option Plans shall be deemed to be
     references to the Parent.

(b)  In the event that the Common Stock Purchase Warrant issued by the Company
     to Promethean Investment Group, L.L.C. (the "Warrant Holder"), dated
     January  21, 1998 (the "Company Warrant"), exercisable for 25,000 shares of
     Company Common Stock (the "Company Warrant Shares") has not been fully
     exercised at the Effective Time, the Company Warrant shall terminate in
     accordance with its terms.  Upon tender to the

                                      A-8
<PAGE>
 
     Surviving Corporation of the aggregate Purchase Price (as defined in the
     Company Warrant) then in effect under the Company Warrant, the Warrant
     Holder shall be entitled, in accordance with the terms of the Company
     Warrant, to receive that number of shares of Parent Common Stock to which
     the Warrant Holder would have been entitled pursuant to the Exchange Ratio
     if, immediately prior to the Effective Time, the Warrant Holder had fully
     exercised the Company Warrant and had been a stockholder of record of the
     Company.


(c)  On the Effective Date, the Parent shall file, and thereafter shall maintain
     the effectiveness of, a registration statement with the Securities and
     Exchange Commission (the "SEC") covering the Unexercised Options and the
     shares issuable under the Company Employee Stock Purchase Plan and the
     Company Warrant Shares and the sale of the Parent Common Stock issued upon
     exercise of the Unexercised Options and, if applicable, the termination of
     the Company Warrant.

(d)  The Employee Stock Purchase Plan of the Company (the "Company Employee
     Stock Purchase Plan") shall remain in effect, without amendment or
     modification, through the Effective Time.

2.4         Closing.
            ------- 

          After all conditions set forth in Article 5 hereof have been satisfied
          (other than those which have been expressly waived), the closing of
          the Merger (the "Closing") shall occur at the offices of Buchanan
          Ingersoll Professional Corporation, 20th Floor, One Oxford Centre,
          Pittsburgh, Pennsylvania, at which the documents to be delivered on
          the Effective Date as described in Article 5 shall be delivered by the
          respective parties.  The Closing shall be scheduled to occur on the
          date set for the Stockholders Meeting as described in Section 4.1(m)
          hereof and immediately after the Stockholders Meeting but in no event
          later than 3:00 p.m., Eastern time (the "Scheduled Closing Date").
          The Closing shall occur on the Scheduled Closing Date unless, on such
          date, any party has a right not to close the Merger and refuses to
          close, in which event the Closing shall be adjourned from Business Day
          to Business Day thereafter until the Closing occurs or until 5:01
          p.m., Eastern time, on November 30, 1998.  As used in this Agreement,
          the term "Business Day" shall mean any day on which the NYSE is open
          for trading.

3.          REPRESENTATIONS, WARRANTIES AND AGREEMENTS.
            ------------------------------------------ 
3.1         Representations, Warranties and Agreements of the Company.
            --------------------------------------------------------- 
          The Company represents and warrants to the Parent and the Merger
          Subsidiary as follows:

                                      A-9
<PAGE>
 
(a)  Organization, Standing and Power.

     (i)  The Company is a corporation duly organized, validly existing and in 
          good standing under the laws of the State of Delaware with all
          requisite corporate power and authority to own, operate and lease its
          properties, to carry on its business as now being conducted, to enter
          into this Agreement and, subject to the approval of the Company's
          stockholders in accordance with the DGCL, to perform its obligations
          hereunder. The Company is duly qualified or licensed to do business
          and in good standing in the state of California and in each other
          jurisdiction which the property owned, leased or operated by it or the
          nature of the business conducted by it makes such qualification or
          licensing necessary, except where the failure to be so qualified or so
          licensed would not, individually or in the aggregate, have a Material
          Adverse Effect on the Company. For purposes of this Agreement,
          "Material Adverse Change" or "Material Adverse Effect" means, when
          used with respect to the Parent or the Company, as the case may be,
          any event, circumstance, change or effect that is or could reasonably
          be expected (as far as can be foreseen at the time) to be so adverse
          as to result in a severe and critical impairment of the business,
          assets, liabilities, financial condition or results of operations of
          the Parent and its Subsidiaries, taken as a whole, or the Company and
          PL, taken as a whole, as the case may be.

     (ii) The Company has only one subsidiary, Penederm Limited (Company No.
          3076653), a company incorporated in England and Wales ("PL"). PL is a
          corporation duly organized and validly existing under the laws of
          England and Wales with all corporate power and authority to own,
          operate and lease its properties and to carry on its business as now
          being conducted. The authorized share capital of PL is (Pounds)1,000
          divided into 1,000 shares of (Pounds)1 each. All of the issued and
          outstanding shares of PL are allotted to the Company free and clear of
          all security interests, liens, claims, pledges, charges or other
          encumbrances of any nature whatsoever, and all such shares have been
          validly issued, fully paid and nonassessable and free of preemptive
          rights. There are no outstanding rights, options, warrants, conversion
          rights or agreements for the purchase or acquisition from, or the sale
          or issuance by, PL of any of its shares.

(b)  Capital Structure.

     (i)  As of the date hereof, the authorized capital stock of the Company 
          consists of 30,000,000 shares of Company Common Stock and

                                     A-10
<PAGE>
 
          10,000,000 shares of preferred stock, par value $.01 per share (the
          "Company Preferred Stock"). At the close of business on June 15, 1998,
          8,620,203 shares of Company Common Stock were issued and outstanding,
          all of which were validly issued, fully paid and nonassessable, and
          free of preemptive rights. As of the date hereof: (A) no shares of
          Company Common Stock are held in the treasury of the Company or PL;
          (B) 1,487,664 shares of Company Common Stock are reserved for future
          issuance pursuant to the Company Stock Option Plans; (C) 25,000 shares
          are reserved for issuance under the Company Warrant; (D) 727,518
          shares are reserved for issuance under that certain Common Stock
          Investment Agreement dated as of January 21, 1998 between Promethean
          Investment Group L.L.C. (the "Investor") and the Company (the "Common
          Stock Investment Agreement"); (E) 70,516 shares are reserved for
          issuance under the Company Employee Stock Purchase Plan; and (F)
          30,000 shares are reserved for issuance under the 401(k) Plan of the
          Company (the "Company 401(k) Plan"). The Company Stock Option Plans,
          the Company Warrant, the Common Stock Investment Agreement, the
          Company Employee Stock Purchase Plan and the Company 401(k) Plan are
          the only benefit plans or arrangements of the Company or PL under
          which any securities of the Company or PL are issuable. No shares of
          Company Preferred Stock are issued and outstanding. As of the date of
          this Agreement, except as set forth above, no shares of capital stock
          or other voting securities of the Company or PL are issued, reserved
          for issuance or outstanding. As of the date of this Agreement, except
          for stock options covering not in excess of 1,220,097 shares of
          Company Common Stock issued under the Company Stock Option Plans
          (collectively, the "Company Stock Options"), the Company Warrant and
          rights to purchase covering approximately 10,000 shares of Company
          Common Stock under the Company Employee Stock Purchase Plans and the
          Company's matching contribution obligations under the 401(k) Plan,
          there are no options, warrants, calls, rights or agreements to which
          the Company or PL is a party or by which either of them is bound
          obligating the Company or PL to issue, deliver or sell, or cause to be
          issued, delivered or sold, additional shares of capital stock of the
          Company or PL or obligating the Company or PL to grant, extend or
          enter into any such option, warrant, call, right or agreement. The
          Company does not have any outstanding bonds, debentures, notes or
          other obligations the holders of which have the right to vote (or
          convertible into or exercisable for securities having the right to
          vote) with the stockholders of the Company on any matter. There are no
          obligations, contingent or otherwise, of the Company to (x)
          repurchase, redeem or otherwise acquire any

                                     A-11
<PAGE>
 
          shares of Company Common Stock or other capital stock of the Company,
          or the capital stock or other equity interests of PL; (y) (other than
          advances to PL in the ordinary course of business) provide material
          funds to, or make any material investment in (in the form of a loan,
          capital contribution or otherwise), or provide any guarantee with
          respect to the obligations of, PL or any other Person; or (z) make
          payment of any Shortfall Compensation (as defined in the Common Stock
          Investment Agreement) to the Investor. The Company contributed 4,651
          shares of Company Common Stock to the Company 401(k) Plan in respect
          of the plan year ended December 31, 1997.

     (ii) The Company has made available to the Parent complete and correct 
          copies of the Company Stock Option Plans, the Company Employee Stock
          Purchase Plan, the Common Stock Investment Agreement, the Company
          401(k) Plan and the Company Warrant. Schedule 3.1(b) sets forth a
                                               ---------------  
          complete and accurate list of (A) all Company Stock Options
          outstanding as of the date of this Agreement and (B) the exercise
          price of each outstanding Company Stock Option.

(c)  Authority.  On or prior to the date of this Agreement, the Board of 
     Directors of the Company has determined the Merger to be advisable and fair
     to and in the best interest of the Company and its stockholders, approved
     this Agreement in accordance with the DGCL, resolved (subject to its
     fiduciary duties) to recommend the approval of this Agreement by the
     Company's stockholders and directed that this Agreement be submitted to the
     Company's stockholders for approval. The Company has all requisite
     corporate power and authority to enter into this Agreement and the Company
     Option Agreement, to consummate the transactions contemplated by the
     Company Option Agreement and, subject to approval by the stockholders of
     the Company of this Agreement, to consummate the transactions contemplated
     hereby. The execution and delivery of this Agreement and the Company Option
     Agreement by the Company and the consummation by the Company of the
     transactions contemplated hereby and thereby have been duly authorized by
     all necessary corporate action on the part of the Company, subject, in the
     case of this Agreement, to (x) approval of this Agreement by the
     stockholders of the Company and (y) the filing of a Certificate of Merger
     as required by the DGCL. This Agreement and the Company Option Agreement
     have been duly executed and delivered by the Company and (assuming the
     valid authorization, execution and delivery of this Agreement by the Parent
     and the Merger Subsidiary and the Company Option Agreement by the Parent
     and the validity and binding effect of this Agreement on the Parent and the
     Merger Subsidiary and the Company Option Agreement on the Parent)
     constitute

                                     A-12
<PAGE>
 
     the valid and binding obligation of the Company enforceable against the
     Company in accordance with their respective terms, except to the extent
     that enforceability thereof may be limited by applicable bankruptcy,
     insolvency, reorganization or other similar laws affecting the enforcement
     of creditors' rights generally and by principles of equity regarding the
     availability of remedies. The Company has taken all necessary action to
     render its Shareholders Rights Plan dated November 20, 1996 (the "Company
     Rights Plan") inapplicable to the transactions contemplated by this
     Agreement. The filing of a combined prospectus and proxy statement to be
     included in the Registration Statement (together with any amendments or
     supplements thereto, the "Prospectus/Proxy Statement") with the SEC and the
     issuance of the shares of Company Common Stock pursuant to the Company
     Option Agreement have been duly authorized by the Company's Board of
     Directors.


(d)  Consents and Approvals; No Violation.  Assuming that all consents, 
     approvals, authorizations and other actions described in this Section
     3.1(d) have been obtained and all filings and obligations described in this
     Section 3.1(d) have been made, except as set forth on Schedule 3.1(d), the
                                                           ---------------
     execution and delivery of this Agreement and the Company Option Agreement
     do not, and the consummation of the transactions contemplated hereby and
     thereby and compliance with the provisions hereof and thereof will not,
     result in any violation of, or default (with or without notice or lapse of
     time, or both) under, or give to others a right of termination,
     cancellation or acceleration of any obligation or the loss of a material
     benefit under, or result in the creation of any lien, security interest,
     charge or encumbrance upon any of the properties or assets of the Company
     or PL under, any provision of (i) the Certificate of Incorporation or
     Bylaws of the Company, (ii) any provision of the charter or organization
     documents of PL, (iii) any loan or credit agreement, note, bond, mortgage,
     indenture, lease or other agreement, instrument, permit, concession,
     franchise or license applicable to the Company or PL, including, without
     limitation, the intellectual property listed on Schedule 3.1(x) and the in-
                                                     ---------------
     licenses, out-licenses, co-promotion and co-marketing agreements listed on
     Schedule 3.1(bb), or (iv) any judgment, order, decree, statute, law,
     ----------------
     ordinance, rule or regulation applicable to the Company or PL or any of
     their respective properties or assets, other than, in the case of clauses
     (ii), (iii) or (iv), any such violations, defaults, rights, liens, security
     interests, charges or encumbrances that, individually or in the aggregate,
     would not have a Material Adverse Effect on the Company, materially impair
     the ability of the Company to perform its obligations hereunder or under
     the Company Option Agreement or prevent the consummation of any of the
     transactions contemplated hereby or thereby. No filing or registration
     with, or authorization, consent or approval of, any domestic (federal and
     state), foreign or supranational court, commission, governmental body,

                                     A-13
<PAGE>
 
     regulatory agency, authority or tribunal (a "Governmental Entity") is
     required by or with respect to the Company or PL in connection with the
     execution and delivery of this Agreement or the Company Option Agreement by
     the Company or is necessary for the consummation of the Merger and the
     other transactions contemplated by this Agreement or the Company Option
     Agreement, except for (i) in connection, or in compliance, with the
     provisions of the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as
     amended (the "HSR Act"), the Securities Act of 1933, as amended (together
     with the rules and regulations promulgated thereunder, the "Securities
     Act") and the Securities Exchange Act of 1934, as amended (together with
     the rules and regulations promulgated thereunder, the "Exchange Act"), (ii)
     the filing of the Certificate of Merger with the Secretary of State of the
     State of Delaware and appropriate documents with the relevant authorities
     of other states in which the Company is qualified to do business, (iii)
     such filings, registrations, authorizations, consents or approvals as may
     be required with respect to PL, (iv) applicable requirements, if any, of
     the National Association of Securities Dealers ("NASD") and the National
     Association of Securities Dealers Automated Quotation National System
     ("NASDAQ"), (v) as may be required under foreign laws, (vi) the consents
     and approvals listed on Schedule 3.1(d), and (vii) such other consents,
                             ---------------
     orders, authorizations, registrations, declarations and filings the failure
     of which to be obtained or made would not, individually or in the
     aggregate, have a Material Adverse Effect on the Company, materially impair
     the ability of the Company to perform its obligations hereunder or under
     the Company Option Agreement or prevent the consummation of any of the
     transactions contemplated hereby or thereby.

(e)  SEC Documents and Other Reports.  The Company has filed all required 
     documents with the SEC since January 1, 1995 (the "Company SEC Documents").
     As of their respective dates, the Company SEC Documents complied in all
     material respects with the requirements of the Securities Act or the
     Exchange Act, as the case may be, and, at the respective times they were
     filed, none of the Company SEC Documents contained any untrue statement of
     a material fact or omitted to state a material fact required to be stated
     therein or necessary to make the statements therein, in light of the
     circumstances under which they were made, not misleading. The consolidated
     financial statements (including, in each case, any notes thereto) of the
     Company included in the Company SEC Documents (the "Company Financial
     Statements") as of their respective dates complied as to form in all
     material respects with applicable accounting requirements and the published
     rules and regulations of the SEC with respect thereto, were prepared in
     accordance with generally accepted accounting principles (except, in the
     case of the unaudited statements, as permitted by Form 10-Q of the SEC)
     applied on a consistent basis during the periods involved

                                     A-14
<PAGE>
 
     (except as may be indicated therein or in the notes thereto) and fairly
     presented in all material respects the consolidated financial position of
     the Company and PL as at the respective dates thereof and the consolidated
     results of their operations and their consolidated cash flows for the
     periods then ended. Except as disclosed in the Company SEC Documents or as
     required by generally accepted accounting principles, the Company has not,
     since March 31, 1998, made any change in the accounting practices or
     policies applied in the preparation of the Company Financial Statements.
     Neither the Company nor PL had as of March 31, 1998 any liabilities or
     obligations of any nature, whether or not accrued, contingent or otherwise,
     that would be required by generally accepted accounting principles to be
     reflected on the consolidated balance sheet of the Company and PL at March
     31, 1998 (including the notes thereto) included in the Company Financial
     Statements that are not so reflected.

(f)  Registration Statement and Prospectus/Proxy.  None of the information to 
     be supplied by the Statement Company (as to the Company) for inclusion or
     incorporation by reference in the Registration Statement or the
     Prospectus/Proxy Statement will (i) in the case of the Registration
     Statement, at the time it becomes effective, contain any untrue statement
     of a material fact or omit to state any material fact required to be stated
     therein or necessary in order to make the statements therein not misleading
     or (ii) in the case of the Prospectus/Proxy Statement, at the time of the
     mailing of the Prospectus/Proxy Statement, at the time of the Stockholders
     Meeting and at the Effective Time, contain any untrue statement of a
     material fact or omit to state any material fact required to be stated
     therein or necessary in order to make the statements therein, in light of
     the circumstances under which they are made, not misleading. If, at any
     time prior to the Effective Time, any event with respect to the Company,
     its officers and directors or PL shall occur which is required at that time
     to be described in the Prospectus/Proxy Statement, such event shall be so
     described, and an appropriate amendment or supplement shall be promptly
     filed with the SEC and, as required by law, disseminated to the
     stockholders of the Company. The Prospectus/Proxy Statement will comply
     (with respect to the Parent) as to form in all material respects with the
     provisions of the Securities Act, and (with respect to the Company) as to
     form in all material respects with the provisions of the Exchange Act.


(g)  Absence of Certain Changes or Events.  Except as disclosed in the
     Company SEC Documents filed with the SEC prior to the date of this
     Agreement, since March 31, 1998 and except as set forth on Schedule 3.1(g),
                                                                ----------------
     (i) the Company and PL have not incurred any material liability or
     obligation (indirect, direct or contingent), or entered into any material
     oral or written agreement or other transaction, that is not in the ordinary
     course of business consistent with past practice or that would

                                     A-15
<PAGE>
 
     result in a Material Adverse Effect on the Company; (ii) the Company and PL
     have not sustained any loss or interference with their business or
     properties from fire, flood, windstorm, accident or other calamity (whether
     or not covered by insurance) that has had a Material Adverse Effect on the
     Company; (iii) there has been no change in the capital stock of the Company
     except for the issuance of shares of Company Common Stock pursuant to
     Company Stock Options and the Company Employee Stock Purchase Plan and no
     dividend or distribution of any kind declared, paid or made by the Company
     on any class of its stock; (iv) there has not been (A) any granting by the
     Company or PL to any executive officer of the Company or PL of any increase
     in compensation, except in the ordinary course of business consistent with
     prior practice or as was required under employment agreements in effect as
     of the date of the most recent audited financial statements included in the
     Company SEC Documents, (B) any granting by the Company or PL to any such
     executive officer of any increase in severance or termination agreements in
     effect as of the date of the most recent audited financial statements
     included in the Company SEC Documents, or (C) any entry by the Company or
     PL into any employment, severance or termination agreement with any such
     executive officer; (v) any delivery of a "put notice," as defined in the
     Common Stock Investment Agreement, or any issuance of any shares of Company
     Common Stock pursuant to the Common Stock Investment Agreement; and (vi)
     there has been no event causing a Material Adverse Effect on the Company or
     any developments that would, individually or in the aggregate, result in a
     Material Adverse Effect on the Company.

(h)  Permits and Compliance.  Each of the Company and PL is in possession of 
     all franchises, grants, authorizations, licenses, permits, easements,
     variances, exceptions, consents, certificates, approvals and orders of any
     Governmental Entity necessary for the Company or PL to own, lease and
     operate its properties or to carry on its business as it is now being
     conducted (the "Company Permits"), except where the failure to have any of
     the Company Permits would not, individually or in the aggregate, have a
     Material Adverse Effect on the Company, and, as of the date of this
     Agreement, no suspension or cancellation of any of the Company Permits is
     pending or, to the knowledge of the Company, threatened, except where the
     suspension or cancellation of any of the Company Permits would not,
     individually or in the aggregate, have a Material Adverse Effect on the
     Company. Neither the Company nor PL is in violation of (i) its charter, by-
     laws or other organizational documents, (ii) any applicable law, ordinance,
     administrative or governmental rule or regulation, or (iii) any order,
     decree or judgment of any Governmental Entity having jurisdiction over the
     Company or PL, except, in the case of clauses (i), (ii) and (iii), for any
     violations that, individually or in the aggregate, would not have a
     Material Adverse Effect on the Company. Except as set forth in the

                                     A-16
<PAGE>
 
     Company SEC Documents filed prior to the date of this Agreement, no event
     of default or event that, but for the giving of notice or the lapse of time
     or both, would constitute an event of default exists or, upon the
     consummation by the Company of the transactions contemplated by this
     Agreement or the Company Option Agreement, will exist under any indenture,
     mortgage, loan agreement, note or other agreement or instrument for
     borrowed money, any guarantee of any agreement or instrument for borrowed
     money or any lease, contractual license or other agreement or instrument to
     which the Company or PL is a party or by which the Company or PL is bound
     or to which any of the properties, assets or operations of the Company or
     PL is subject, other than any defaults that, individually or in the
     aggregate, would not have a Material Adverse Effect to on the Company. On
     May 13, 1998, the Company's revolving credit facility with Silicon Valley
     Bank terminated in accordance with the terms thereof, the Company having
     satisfied in full all of its obligations thereunder.


(i)  Tax Matters.  Except as set forth on Schedule 3.1(i), (i) the
                                          ---------------         
     Company and PL have filed all federal, and all material state, local,
     foreign and provincial, Tax Returns required to have been filed or
     appropriate extensions therefor have been properly obtained, and such Tax
     Returns are correct and complete, except to the extent that any failure to
     so file or any failure to be correct and complete would not, individually
     or in the aggregate, have a Material Adverse Effect on the Company; (ii)
     all Taxes shown to be due on such Tax Returns have been timely paid or
     extensions for payment have been properly obtained; (iii) the Company and
     each of its Subsidiaries have complied in all material respects with all
     rules and regulations relating to the withholding of Taxes except to the
     extent that any failure to comply with such rules and regulations would
     not, individually or in the aggregate, have a Material Adverse Effect on
     the Company; (iv) neither the Company nor PL has waived or extended any
     statute of limitations in respect of its Taxes; (v) to the knowledge of the
     Company, no Tax Returns referred to in clause (i) relating to federal and
     state income Taxes have been examined by the Internal Revenue Service
     ("IRS") or the appropriate state taxing authority for any period; (vi) no
     issues have been raised in writing by the relevant taxing authority in
     connection with the examination of the Tax Returns referred to in clause
     (i); (vii) all deficiencies asserted or assessments made as a result of any
     examination of such Tax Returns by any taxing authority have been paid in
     full or are being timely and properly contested; and (viii) the Company is
     not a "United States real property holding company" as defined in Section
     897(c) of the Code. The Company has not filed a consent of the type
     described in Section 341(f) of the Code. The Company is not and has never
     been a member of an affiliated group of corporations (within the meaning of
     Section 1504 of the Code). The

                                     A-17
<PAGE>
 
     Company is not a party to, is not bound by and does not have any obligation
     under any tax sharing, tax indemnity or similar agreement. For purposes of
     this Agreement: (i) "Taxes" means any federal, state, local, foreign or
     provincial income, gross receipts, property, sales, use, license, excise,
     franchise, employment, payroll, withholding, alternative or added minimum,
     ad valorem, value-added, transfer or excise tax, or other tax, custom,
     duty, governmental fee or other like assessment or charge of any kind
     whatsoever, together with any interest or penalty imposed by any
     Governmental Entity, and (ii) "Tax Return" means any return, report or
     similar statement (including the attached schedules) required to be filed
     with respect to any Tax, including, without limitation, any information
     return, claim for refund, amended return or declaration of estimated Tax.


(j)  Actions and Proceedings.  Except as set forth in the Company SEC
     Documents filed prior to the date of this Agreement or on Schedule 3.1(j),
                                                               ---------------
     there are no outstanding orders, judgments, injunctions, awards or decrees
     of any Governmental Entity against or involving the Company or PL, or
     against or involving any of its or their present or, to the knowledge of
     the Company, former directors, officers, employees, consultants or agents
     of the Company or PL, in their capacities as such, any of its or their
     properties, assets or business or any Employee Benefit Plan of the Company
     that, individually or in the aggregate, would have a Material Adverse
     Effect on the Company or materially impair the ability of the Company to
     perform its obligations hereunder or under the Company Option Agreement. As
     of the date of this Agreement, there are no actions, suits, labor disputes
     or claims or legal, administrative or arbitrative proceedings or
     governmental investigations pending or, to the knowledge of the Company,
     threatened against or involving the Company or PL or any of its or their
     present or, to the knowledge of the Company, former directors, officers,
     employees, consultants or agents in their capacities, as such, or any of
     its or their properties, assets or business or any Employee Benefit Plan of
     the Company that, individually or in the aggregate, would have a Material
     Adverse Effect on the Company or materially impair the ability of the
     Company to perform its obligations hereunder or under the Company Option
     Agreement. As of the date hereof, there are no actions, suits, labor
     disputes or other litigation, legal or administrative proceedings or
     governmental investigations pending or, to the knowledge of the Company,
     threatened against or affecting the Company or PL or any of its or their
     present or, to the knowledge of the Company, former officers, directors,
     employees, consultants or agents, in their capacities as such, or any of
     its or their properties, assets or business relating to the transactions
     contemplated by this Agreement and the Company Option Agreement. For
     purposes of this Agreement, the term "knowledge of the Company" shall mean
     the actual knowledge of the officers and directors of the Company.

                                     A-18
<PAGE>
 
(k)  FDA and Related Matters.

(i)  Schedule 3.1(k) sets forth a list, for the period between January 1, 1993
     ---------------                                                          
     and the date hereof, of (A) all Regulatory or Warning Letters, Notices of
     Adverse Findings and Section 305 Notices and similar letters or notices
     issued by the Food and Drug Administration ("FDA") (or any other federal,
     state, local or foreign governmental entity that is concerned with the
     safety, efficacy, reliability or manufacturing of drug products (each, a
     "Drug Regulatory Agency")) to the Company or PL that, individually or in
     the aggregate, would have a Material Adverse Effect on the Company, (B) all
     product recalls, notifications and safety alerts conducted by the Company
     or PL, whether or not required by the FDA, and any request from the FDA or
     any Drug Regulatory Agency requesting the Company or PL to cease to
     investigate, test or market any product, which recalls, notifications,
     safety alerts or requests would, individually or in the aggregate, have a
     Material Adverse Effect on the Company, and (C) any criminal, injunctive,
     seizure or civil penalty actions begun or threatened by the FDA or any Drug
     Regulatory Agency against the Company or PL and known by the Company or PL
     and all related consent decrees (including plea agreements) issued with
     respect to the Company or PL.  Copies of all documents referred to in
     Schedule 3.1(k) have been made available to the Parent.
     ---------------                                        

(ii) The Company has made submissions to obtain material approvals,
     certifications, authorizations, clearances and permits for marketing, and
     has made filings with, or notifications to, the FDA and Drug Regulatory
     Agencies (or has documented a basis for not making such filings or
     notifications) pursuant to applicable requirements of the Federal Food,
     Drug and Cosmetics Act, as amended (the "FDA Act"), and applicable laws,
     regulations and rules with respect to each of the products sold by the
     Company or PL that is listed on Schedule 3.1(k).  The products listed on
                                     ---------------                         
     Schedule 3.1(k) collectively constitute in excess of 95% of the gross
     ---------------                                                      
     revenues generated during the twelve (12)-month period ending December 31,
     1997 by that portion of the business of the Company and PL which is subject
     to the jurisdiction of the FDA or any Drug Regulatory Agency.  The Company
     and PL have no reason to believe that any of the material approvals,
     clearances, authorizations, registrations, certifications, permits, filings
     or notifications that it or any of its Subsidiaries has received or made to
     the FDA or any Drug Regulatory Agency that relate to the marketing of the
     products listed on Schedule 3.1(k) have been or are being revoked;
                        ---------------                                
     provided, however, the FDA or any other Drug

                                     A-19
<PAGE>
 
      Regulatory Agency may disagree with the Company's or PL's assessment and
      undertake actions, at any time, to remove from commercial distribution any
      such product.

(iii) Except as disclosed on Schedule 3.1(k), neither the Company nor PL
                             ---------------                          
has knowledge (or has been notified by the Contract Manufacturer) of any pending
regulatory action of any sort (other than non-material routine or periodic
inspections or reviews) against any of the Company, PL or the contract
manufacturer of the Company's products (the "Contract Manufacturer") by the FDA
or any Drug Regulatory Agency or any other duly authorized governmental
authority which regulates the sale of drugs in any jurisdiction which could have
a Material Adverse Effect on the Company or in any material way limit or
restrict the ability of the Company or PL to market existing products.  Except
as set forth on Schedule 3.1(k), none of the Company, PL or, to the knowledge of
                ---------------                                                 
the Company, the Contract Manufacturer has knowingly committed or permitted to
exist any violation of the rules and regulations of the FDA or any Drug
Regulatory Agency or any other duly authorized governmental authority which
regulates the sale of drugs which has not been cured by the Company, PL or, to
the knowledge of the Company, the Contract Manufacturer or waived by the FDA or
any such regulatory authority; provided, however, the FDA or any other Drug
Regulatory Agency may disagree with the Company's assessment and undertake
enforcement actions at any time.

(l)  Certain Agreements.  Except as set forth in Schedule 3.1(l), neither
                                                 ---------------
     the Company nor PL is a party to any oral or written employment agreement
     or plan, including any employment agreement, severance agreement, stock
     option plan, stock appreciation rights plan, restricted stock plan or stock
     purchase plan, any of the benefits of which shall be increased, or the
     vesting of the benefits of which will be accelerated, by the occurrence of
     any of the transactions contemplated by this Agreement or the Company
     Option Agreement or the value of any of the benefits of which will be
     calculated on the basis of any of the transactions contemplated by this
     Agreement or the Company Option Agreement (collectively, "Transaction
     Agreements"). No holder of any option to purchase shares of Company Common
     Stock, or shares of Company Common Stock granted in connection with the
     performance of services for the Company or PL, is or will be entitled to
     receive cash from the Company or PL in lieu of or in exchange for such
     option or shares as a result of the transactions contemplated by this
     Agreement or the Company Option Agreement. Schedule 3.1(l) sets forth (i)
                                                --------------
     for each officer, director or employee who is a party to, or will receive
     benefits (other than as a result of Section 2.3)

                                     A-20
<PAGE>
 
     under, any Transaction Agreement, the total amount that each such Person
     may receive, or is eligible to receive, assuming that the transactions
     contemplated by this Agreement are consummated on the date hereof, and (ii)
     the total amount of indebtedness owed to the Company or PL from each
     officer or director of the Company and PL. Except as set forth in the
     Certificate of Incorporation and Bylaws of the Company or PL, neither the
     Company nor PL is a party to any indemnification agreement with any of its
     present or future directors, officers, employees, agents or other Persons
     who serve or served in any other capacity with any other enterprise at the
     request of the Company or of PL.

(m)  Material Contracts.  Except as set forth in Schedule 3.1(m) or on any
                                                 ---------------
     other Schedule hereto, as of the date hereof, neither the Company nor PL is
     a party to, or is bound by, (i) any material agreement, indenture or other
     instrument relating to the borrowing of money by the Company or PL or the
     guarantee by the Company or PL of any such obligation (other than trade
     payables and instruments relating to transactions entered into in the
     ordinary course of business) or (ii) any other material contract or
     agreement or amendment thereto that (A) is not described in, or filed as an
     exhibit to, a Form 10-K, a Form 10-Q or a Form 8-K filed by the Company
     with the SEC, (B) places any material restrictions on the ability of the
     Company to engage in any material business activity currently conducted, or
     (C) is material to the business, properties, assets, liabilities, financial
     condition, results of operations or prospects of the Company and PL, taken
     as a whole (collectively, the "Company Contracts"). Neither the Company nor
     PL is in default under any Company Contract, which default is reasonably
     likely to have, either individually or in the aggregate, a Material Adverse
     Effect on the Company, and there has not occurred any event that with the
     lapse of time or the giving of notice or both would constitute such a
     default.


(n)  Opinion of Financial Advisor.  The Company has received the written 
     opinion of Lehman Brothers Inc., dated the date hereof, to the effect that,
     as of the date hereof, from a financial point of view, the Exchange Ratio
     to be offered to the stockholders of the Company is fair to the Company's
     stockholders, a copy of which opinion has been delivered to the Parent.

(o)  Takeover Provisions Inapplicable.  As of the date hereof and at all times 
     on or prior to the Effective Time, Section 203 of the DGCL is, and shall
     be, inapplicable to the Merger, the Company Option Agreement, the Voting
     Agreements and the transactions contemplated thereby.

(p)  Required Vote of the Company Stockholders.  The affirmative vote of the 
     holders of a majority of the outstanding shares of Company Common Stock is
     required to adopt this Agreement. No other vote of the

                                     A-21
<PAGE>
 
     securityholders of the Company is required by law, the Certificate of
     Incorporation or Bylaws of the Company or otherwise in order for the
     Company to consummate the Merger and the transactions contemplated hereby
     and in the Company Option Agreement.


(q)  Finders and Investment Bankers.  Except for Lehman Brothers, Inc., whose 
     fees will be paid by the Company, there is no investment banker, broker,
     finder or other intermediary which has been retained by or is authorized to
     act on behalf of the Company or PL who might be entitled to any fee or
     commission in connection with the transactions contemplated by this
     Agreement.

(r)  Authorized Stock.  The Company has taken all necessary corporate
     and other action to authorize and reserve and to permit it to issue, and,
     at all times from the date hereof until the obligation to deliver Common
     Stock when the Company Option Agreement terminates, will have reserved for
     issuance, upon exercise of the Option (as defined in the Company Option
     Agreement), shares of Common Stock necessary for the Parent to exercise the
     Option, and the Company shall take all necessary corporate action to
     authorize and reserve for issuance all additional shares of Common Stock or
     other securities which may be issued pursuant to the Company Option
     Agreement upon exercise of the Option. The shares of Common Stock to be
     issued upon due exercise of the Option, including all additional shares of
     Common Stock or other securities which may be issuable pursuant to the
     Company Option Agreement, upon issuance pursuant thereto, shall be duly and
     validly issued, fully paid and nonassessable and shall be delivered free
     and clear of all liens or encumbrances of any kind or nature whatsoever,
     including any preemptive rights of any stockholder.

(s)  Company Affiliates.  Schedule 3.1(s) contains a list (reasonably
                          ---------------
     satisfactory to counsel for the Parent) identifying all Persons who may be
     deemed to be "affiliates" of the Company on the date hereof as that term is
     used in paragraphs (c) and (d) of Rule 145 under the Securities Act (the
     "Company Affiliates").

(t)  Owned Real Property.  The Company owns no real property.

(u)  Leased Real Estate.  The Company is the lessee under the real estate
     leases described on Schedule 3.1(u). Schedule 3.1(u) contains the number of
                         ---------------  ---------------
     square feet leased by the Company under each lease, the current rent
     payable thereunder and the expiration date of each lease. True, correct and
     complete copies of said leases have been delivered by the Company to the
     Parent. The Company now enjoys quiet and undisturbed possession under each
     of said leases. To the knowledge of the Company, such leased real estate is
     free and clear of any zoning, use or building restriction or any

                                     A-22
<PAGE>
 
     pending, proposed or threatened zoning or use or building restriction which
     would, either singly or in the aggregate, adversely interfere with the
     present or any intended use of any of such leased real estate. To the
     knowledge of the Company, said leases are valid and binding and in full
     force and effect. The Company is not in default as to the payment of rent
     and has not received written notice of any other default thereunder.


(v)  Owned and Leased Tangible Personal Property.  Title to all of the 
     Company's owned equipment, vehicles, furniture and fixtures and other items
     of owned tangible personal property is held by the Company free and clear
     of any claim, lease, mortgage, security interest, conditional sale
     agreement or other title retention agreement, restriction or lien or
     encumbrance of any kind or nature whatsoever, except as set forth on
     Schedule 3.1(v). The Company has a valid leasehold interest in all tangible
     ---------------
     personal property material to its business held by it under lease, and
     true, correct and complete copies of said leases have been delivered by the
     Company to the Parent. To the knowledge of the Company, said leases are
     valid and binding and in full force and effect. The Company is not in
     default as to the payment of rent and has not received written notice of
     any other default thereunder.

(w)  Physical Condition of Property.  To the knowledge of the Company, all of 
     the leased real estate of the Company and the structures erected thereon
     and all of the owned and leased tangible personal property of the Company
     are in good repair and condition and are suitable for the conduct of the
     present business of the Company.

(x)  Patents and Certain Other Intellectual Property Rights.


(i)  Schedule 3.1(x) lists all of the patents (including all reissues,
     ---------------                                                  
     divisions, continuations and extensions thereof), patent applications,
     patent disclosures, docketed inventions, trademarks, trademark
     applications, trade names and copyrights owned by the Company.

(ii) The Company owns, or possesses the right to use, all of the intellectual
     property rights necessary to the conduct of the business of the Company as
     presently conducted except for rights which, if not so owned or possessed,
     would not individually or in the aggregate have a Material Adverse Effect
     on the Company.  Such ownership or right to use, as the case may be, is
     free and clear of all liens, security interests, claims and rights to use
     of third parties except those which would not, individually or in the
     aggregate, have a Material Adverse Effect on the Company.

                                     A-23
<PAGE>
 
(iii)Except pursuant to licenses listed in Schedule 3.1(bb) or in the Company 
                                           ----------------
     SEC Documents, there are no material royalties, honoraria, fees or other
     payments payable as of the date hereof by the Company to any person by
     reason of the ownership, use, license, sale or disposition of any of the
     Company's intellectual property rights.

(iv) The Company is not, to the knowledge of the Company, infringing the right
     of any other party with respect to any intellectual property rights which
     would, individually or in the aggregate, be reasonably likely to have a
     Material Adverse Effect on the Company.

(y)  Accounts Receivable.  No customer(s) representing 10% or more of the 
     total revenues of the Company is (are) delinquent in the payment of its
     (their) accounts with the Company.

(z)  Insurance and Bonds.  Attached hereto, made part hereof and marked 
     Schedule 3.1(z) is a true and correct listing of all of the policies of
     ---------------
     insurance and all surety and other bonds to which the Company now is a
     party, or during the immediately preceding sixty (60) months was a party.
     All of such policies and bonds which have expired were valid and in full
     force and effect during their respective terms, all other of such policies
     and bonds are valid and in full force and effect at the present time, and
     no claim has been made, or notice given, to cancel or avoid any of said
     policies or bonds or to reduce the coverage provided thereby, except where
     the existence of any claim or notice of cancellation, avoidance or
     reduction of coverage, or invalidity, unenforceability or ineffectiveness,
     would not have a Material Adverse Effect on the Company.

(aa) Product Warranties and Liability.


(i)  No reserves have been provided for by the Company to cover potential claims
     under existing customer indemnification agreements.

(ii) Except as to claims, actions, proceedings or investigations which have been
     asserted but as to which no notice has been given to the Company, and
     except as set forth on Schedule 3.1(aa), there are no product liability
                            ----------------                                
     claims, actions, proceedings or investigations pending or, to the knowledge
     of the Company, threatened against the Company or its assets or state of
     facts existing which could give rise to any such product liability claim,
     action, proceeding or investigation.

(iii)To the knowledge of the Company, no claims have been made that the 
     products sold by the Company are not effective for the uses

                                     A-24
<PAGE>
 
     such products purport to serve. To its knowledge, the Company has not
     received any written notice that any product manufactured by it has not
     been manufactured in accordance with "current Good Manufacturing Practices"
     (as such term is commonly understood within the Company's industry) or has
     not been properly labeled for its approved use.

(bb) Contracts, Proposals and Bids.  Schedule 3.1(bb) is a list of all of the
                                     ----------------
     in-license, out-license, co-promotion and co-marketing agreements and
     similar agreements relating to the intellectual property rights of the
     Company necessary for the conduct of the business of the Company as
     currently conducted, customer contracts for product sales and all bids or
     proposals for product or customer contracts not yet received, bid or
     awarded.

(cc) Labor and Employment Matters.  Except as set forth on Schedule 3.1(cc):
                                                           ----------------

(i)  The Company is not a party to or obligated to contribute to any employee
     benefit plan as defined in Section 3(3) of the Employee Retirement Income
     Security Act of 1974 ("ERISA") (an "Employee Benefit Plan"), guaranteed
     annual income plan, fund or arrangement, or any incentive, bonus, profit
     sharing, deferred compensation, stock option or purchase plan, agreement or
     arrangement, or any written or, to the knowledge of the Company, oral
     employment or consulting agreement (except employment offer letters), or
     any non-competition agreement, or any severance or written, or to the
     knowledge of Company, oral termination pay plans or policies, any
     hospitalization, disability or other insurance plans, or any other employee
     fringe benefit plans, or any collective bargaining agreement, or any other
     agreement, plan or arrangement similar to or in the nature of the
     foregoing, oral or written, whether or not an Employee Benefit Plan, except
     those set forth on Schedule 3.1(cc).  True, correct and complete copies of
                        ----------------                                       
     all of the written Employee Benefit Plans and other written plans and
     agreements and true, correct and complete written descriptions of all of
     such oral arrangements described in Schedule 3.1(cc) have heretofore been
                                         ----------------                     
     delivered by the Company to the Parent.  The Company does not have any
     unfunded liabilities on account of or in connection with any such Employee
     Benefit Plan, other plan, agreement or arrangement which is a non-
     multiemployer plan.

(ii) With respect to any non-multiemployer Employee Benefit Plan, (A) neither
     such Employee Benefit Plan nor any fiduciary has engaged in a prohibited
     transaction as defined in Section 406 of ERISA (for which no individual or
     class exemption exists under

                                     A-25
<PAGE>
 
     Section 408 of ERISA) or any prohibited transaction as defined in Section
     4975 of the Code (for which no individual or class exemption exists under
     Section 4975 of the Code), which may reasonably be expected to have a
     Material Adverse Effect on the Company; (B) all filings and reports as to
     such Employee Benefit Plan required to have been made on or before the date
     hereof to the IRS, to the United States Department of Labor or, if
     applicable, to the Pension Benefit Guaranty Corporation have been made on
     or before the date hereof (to the extent not granted a valid extension of
     the date of filing); (C) all disclosures to plan participants relating to
     such Employee Benefit Plan required by ERISA to have been made on or before
     the date hereof have been or will be duly made on or before that date; (D)
     there is no litigation, disputed claim (other than routine claims for
     benefits), governmental proceeding or investigation pending or threatened
     with respect to any such Employee Benefit Plan, its related trust or any
     fiduciary, administrator or sponsor of such Employee Benefit Plan; (E) each
     Employee Benefit Plan has been established, maintained, funded and
     administered materially in accordance with its governing documents and any
     applicable provisions of ERISA, the Code, other applicable law and all
     regulations and rulings promulgated thereunder; and (F) the Company has
     delivered to the Parent a true, correct and complete copy of (1) the most
     recent Form 5500 for each such Employee Benefit Plan filed with the IRS and
     the Department of Labor and, with respect to each Employee Benefit Plan
     which is an "employee pension benefit plan" within the meaning of Section
     3(2) of ERISA, the most recent determination letter received from the IRS,
     (2) each trust or custodial agreement and each deposit administration,
     group annuity, insurance or other funding contract associated with such
     Employee Benefit Plan, (3) the most recent financial information for each
     Employee Benefit Plan, (4) where applicable, the most recent actuarial
     report or valuation relating to each such Employee Benefit Plan which has
     been delivered to the Company by its actuaries, and (5) where applicable, a
     summary of any "reportable event" within the meaning of Section 4043(b) of
     ERISA.

(iii)The Company has never been a party to or obligated to contribute to any 
     multiemployer Employee Benefit Plan.

(iv) There has not been any (A) termination or partial termination of any
     Employee Pension Benefit Plan maintained by the Company (or by any Person
     which is or was under common control, within the meaning of Section 414(b),
     (c), (m) or (o) of the Code, with the Company (a "Section 414 Affiliate")
     during the period of such

                                     A-26
<PAGE>
 
     common control, at a time when Title IV of ERISA applied to such Plan, (B)
     commencement of any proceeding to terminate any such Plan pursuant to ERISA
     or otherwise, or (C) written notice given to the Company or any affiliate
     of the intention to commence or seek the commencement of any such
     proceeding, which (under (A)) resulted or (under (B) or (C)) would result
     in an insufficiency of plan assets necessary to satisfy benefit commitments
     under Title IV of ERISA or benefits vested under the Plan. Neither the
     Company nor any Section 414 Affiliate has incurred withdrawal liability,
     complete or partial, contingent or otherwise, under the Multiemployer
     Pension Plan Amendments Act of 1980.

(v)  The Company (A) is not a party to any collective bargaining agreement or
     discussions or negotiations with any Person or group looking toward any
     such agreement, (B) has not within the last three (3) years experienced any
     strike, lockout, work stoppage, slowdown, unfair labor practice claim or
     other labor difficulty (other than grievances and unfair labor practice
     claims in which the Company's only exposure was to monetary damages of
     $50,000 or less), and (C) to the knowledge of the Company, is not aware of
     a threatened strike, lockout, work stoppage, slowdown, unfair labor
     practice claim or other such labor difficulty.  The Company has no
     knowledge of any facts which would form the basis for the assertion of any
     grievance or unfair labor practice claim or other charge or complaint
     against the Company by or before the National Labor Relations Board or any
     state labor relations board or commission or representative thereof, and is
     not aware of any filing by any employee or employee group seeking
     recognition as a collective bargaining representative or unit.

(dd) Insider Contracts.  Except as set forth in the Company SEC Documents or on
     Schedule 3.1(dd) or as set forth and identified as such on any other
     ----------------
     Schedule hereto, there are no contracts, agreements, purchase orders,
     commitments, leases, understandings or arrangements, including loan
     arrangements, between the Company and any of its respective officers
     (except employment offer letters), directors or shareholders, or any
     related or affiliated Person, corporation or other entity (a true, correct
     and complete copy of each such written document and a true, correct and
     complete written description of each such oral relationship having
     heretofore been delivered by the Company to the Parent).

(ee) Other Material Contracts.  Schedule 3.1(ee) is a true, correct and 
                                ---------------
     complete list of all other (i.e., not identified on one or more of the
     foregoing Schedules hereto) material contracts, agreements, understandings
     and arrangements, oral and written, to which the Company is a party or by

                                     A-27
<PAGE>
 
     which the Company is bound. For purposes of this Section 3.1(ee),
     "material" shall mean containing an obligation (i) requiring, or reasonably
     anticipated to require, payment of more than $100,000 in any one (1) year
     period, or (ii) not terminable by or on the Company's behalf, without
     penalty, within ninety (90) days after the Closing, or (iii) terminable by
     or on behalf of the other party on ninety (90) days' notice or less, or
     (iv) having a term of more than twenty-four (24) months, or (v) of guaranty
     or suretyship, irrespective of the term or amount involved. True, correct
     and complete copies of such written material contracts have heretofore been
     delivered by the Company to the Parent. All material contracts are valid
     and binding, in full force and effect and enforceable in accordance with
     their terms, and there exists no default, and to the knowledge of the
     Company, no event has occurred which through notice or the passage of time
     or otherwise may result in a default, under the terms of any of the
     material contracts, except as set forth on Schedule 3.1(ee) and except
                                                ----------------
     where the invalidity, nonbinding nature, unenforceability, ineffectiveness
     or default would not have a Material Adverse Effect on the operations or
     financial condition of the Company taken as a whole.

(ff) Export of Products and Technologies.  To the knowledge of the Company, 
     there are no United States government restrictions prohibiting or, except
     for export licensing requirements which the Company has fulfilled or
     satisfied to date, otherwise affecting the Company in exporting its
     existing products and know-how to the foreign countries to which such are
     currently being exported (a description of all of such products and know-
     how and foreign countries being listed on Schedule 3.1(ff)).
                                               ----------------

(gg) Absence of Illegal Payments.  The Company has not authorized any of its 
     officers, directors, employees or non-employee agents to make, and to the
     knowledge of the Company, no officer, director, employee or non-employee
     agent of the Company has authorized or made, any offer, payment or promise
     to pay any money, or offered, given or promised to give anything of value,
     to any domestic or foreign government official, political party or official
     thereof or any candidate for political office (domestic or foreign), or to
     any other Person, while knowing or having reason to know that all or a
     portion of such money or thing of value would be offered, given or
     promised, directly or indirectly, to any of such Person(s) for purposes of
     (A) influencing any act or decision of such entity or Person, including a
     decision to fail to perform his or her official functions, or (B) inducing
     such entity or Person to use his or her influence with a domestic or
     foreign government or instrumentality thereof to affect or influence any
     act or decision of such government or instrumentality in order to assist
     the Company in obtaining or retaining business for or with, or directing
     business to, any Person, which offer, payment or promise

                                     A-28
<PAGE>
 
     constitutes a violation by the Company of the Foreign Corrupt Practices Act
     of 1977, as amended.

(hh) Absence of Anti-Boycott Violations.  To the knowledge of the Company, the 
     Company has not violated or is not in violation of any statute, law,
     decree, order, rule or regulation of any governmental body of the United
     States which prohibits or regulates the boycotting of or refusal to deal
     with any Person or entity, including without limitation the Export
     Administration Amendments of 1977 (50 U.S.C. App. (S) 2401 et seq.), the
                                                                -------
     Ribicoff Amendments to the Tax Reform Act of 1976 (Internal Revenue Code
     (S) 999) or the Sherman Act (15 U.S.C. (S) l et seq.), or any rule or
                                                  -------
     regulation promulgated pursuant thereto.

(ii) Environmental Matters.

(i)  Except as disclosed in Schedule 3.1(ii):  (A) the Company is currently in
                            ----------------                                  
     compliance with all applicable Environmental Laws, and has obtained all
     permits and other authorizations needed to operate its facilities, except
     where failure to comply with applicable Environmental Laws or where failure
     to obtain such permits and other authorizations would not have a Material
     Adverse Effect on the Company; (B) the Company has not violated any
     applicable Environmental Law, except where such violation would not have a
     Material Adverse Effect; (C) there are no present requirements of any
     applicable Environmental Laws which will increase materially the Company's
     costs of complying with the Environmental Laws nor to the Company's
     knowledge are any such requirements currently threatened to be imposed; (D)
     all past on-site generation, treatment, storage, disposal and other
     management of Regulated Substances by the Company and, to the knowledge of
     Company, by any prior owner, operator or occupant of any property presently
     or previously owned, leased or occupied by the Company was, when done, in
     compliance with then applicable Environmental Laws, except where failure of
     compliance would not have a Material Adverse Effect on the Company; (E) no
     past on-site generation, treatment, storage, disposal or other management
     of Regulated Substances:  (1) has resulted in the presence of Regulated
     Substances on, in, under or migrating from any property of the Company in
     violation of applicable Environmental Laws, except where such violation
     would not have a Material Adverse Effect on the Company; or (2) requires
     the investigation, cleanup, removal or remediation of any Regulated
     Substances, in order to comply with Environmental Laws, except where such
     investigation, cleanup, removal or remediation would not have a Material
     Adverse Effect on the Company; (F) all past

                                     A-29
<PAGE>
 
     off-site transportation, treatment, storage, disposal and other management
     of Regulated Substances generated by the Company was, when done, in
     compliance with then applicable Environmental Laws, except where failure of
     compliance would not have a Material Adverse Effect on the Company; (G) the
     Company did not, directly or indirectly, arrange for the treatment, storage
     or disposal of any Regulated Substances at any property or facility
     identified or, to the knowledge of the Company, is proposed to be
     identified on any list of contaminated properties or other properties which
     pursuant to Environmental Laws are the subject of an investigation or
     remediation action by any federal, state or, to the knowledge of the
     Company, local, government agency or instrumentality; (H) no property
     currently owned, leased or otherwise occupied by the Company and no
     property previously owned, leased or otherwise occupied by the Company is
     identified, or to the knowledge of the Company is proposed to be
     identified, on any list of contaminated properties or other properties
     which pursuant to Environmental Laws are the subject of an investigation or
     remediation action by any federal, state or, to the knowledge of the
     Company, local government agency or instrumentality; (I) the Company has
     not received any notice of any kind that the Company is or may be
     considered a party with potential responsibility under Environmental Laws
     for the costs of responding to a release or threatened release of any
     Regulated Substance which has not been resolved; (J) the Company has not
     filed or failed to file any notice required under any applicable
     Environmental Law reporting a release of any Regulated Substance; (K) no
     environmental lien and no unrecorded environmental lien has attached to any
     property of the Company, nor, to the knowledge of the Company, is there a
     reasonable basis to believe that such a lien may be attached to any
     property of the Company; and (L) during the period when the Company
     occupied any property now or formerly owned, leased or operated by the
     Company or, to the knowledge of the Company, during any period prior to its
     ownership, occupation or operation of such property: (1) there were no
     underground storage tanks or surface impoundments, (2) there was no
     asbestos-containing material in friable form, and (3) there were no
     polychlorinated biphenyls ("PCBs") other than those used, maintained or
     disposed of in compliance with all applicable Environmental Laws.

(ii) As used in this Section 3.1(ii), the following terms shall be defined as
     follows:  (A) "Environmental Laws" include but are not limited to any
     federal, state, local or foreign laws (including the common law), statutes,
     charters, ordinances, codes, rules or regulations,

                                     A-30
<PAGE>
 
     permits or permit conditions, licenses or authorizations, consent or
     administrative orders, agreements or understandings (whether previously
     existing, now existing or hereafter enacted, promulgated, issued or entered
     into) which pertain to the protection of human health or the environment or
     worker safety, including, without limitation, the Comprehensive
     Environmental Response, Compensation and Liability Act, 42 U.S.C. (S) 9601
     et seq.; the Resource Conservation and Recovery Act, 42 U.S.C. (S) 6901
     -- ----              
     et seq.;  the Hazardous Materials Transportation Act, 49 U.S.C. (S) 1801
     -- ----                
     et seq.; the Toxic Substance Control Act, 15 U.S.C. (S) 2601 et seq.; the 
     -- ----                                                      -- ---
     Federal Water Pollution Control Act, 33 U.S.C. (S) 1251 et seq.; the 
                                                             -- ----
     Federal Safe Drinking Water Act, 42 U.S.C. (S)(S) 300f-300j; the Federal 
     Air Pollution Control Act, 42 U.S.C. (S) 7401 et seq.; the Oil Pollution 
                                                   -- ---- 
     Act, 33 U.S.C. (S) 2701 et seq.; the Federal Insecticide, Fungicide and 
                             -- ---- 
     Rotenticide Act, 7 U.S.C. (S)(S) 136-136y; and the Occupational Safety 
     and Health Act, 29 U.S.C. (S) 651 et seq., as each may be amended from 
                                       -- ----                        
     time to time, regulations promulgated under the foregoing or any equivalent
     state statutes and regulation, and any judicial or administrative
     interpretation of such laws, statutes, charters, ordinances, codes, rules
     or regulations, permits or permit conditions, consent or administrative
     orders, agreements or understandings, including, without limitation, any
     judicial or administrative orders or judgments; and (B) "Regulated
     Substance" includes any substance the manufacturing, processing, sale,
     generation, treatment, storage, disposal, transportation, labeling,
     removal, remediation or other management of which is regulated by any
     applicable Environmental Law.

(jj) No Adverse Actions.  There is no existing, pending or, to the
knowledge of the Company, threatened termination, cancellation, limitation,
modification or change in the business relationship of the Company with any
supplier, customer or other Person or entity, except such actions which would
not have a Material Adverse Effect on the Company.

3.2         Representations, Warranties and Agreements of the Parent.
            -------------------------------------------------------- 
          The Parent represents and warrants to the Company as follows:

(a)  Organization, Standing and Power.  The Parent is a corporation
duly organized, validly existing and in good standing under the laws of the
Commonwealth of Pennsylvania with all requisite corporate power and authority to
own, operate and lease its properties, to carry on its business as now being
conducted and to enter into this Agreement and perform its obligations
hereunder.  Each Subsidiary of the Parent is duly organized,

                                     A-31
<PAGE>
 
validly existing and in good standing under the laws of the jurisdiction in
which it is organized and has the requisite corporate power and authority to
carry on its business as now being conducted, except where the failure to be so
organized, existing or in good standing or to have such power or authority would
not, individually or in the aggregate, have a Material Adverse Effect on the
Parent. The Parent and each of its Subsidiaries are duly qualified to do
business, and are in good standing, in each jurisdiction where the character of
their properties owned or held under lease or the nature of their activities
makes such qualification necessary, except where the failure to be so qualified
would not, individually or in the aggregate, have a Material Adverse Effect on
the Parent. For purposes of this Agreement, a "Subsidiary" of the Parent means
any corporation, partnership, limited liability company, joint venture or other
legal entity of which the Parent (either alone or through or together with any
other Subsidiary) owns, directly or indirectly, 50% or more of the stock or
other equity interests the holders of which are generally entitled to vote for
the election of the board of directors or other governing body of such
corporation, partnership, limited liability company, joint venture or other
legal entity.

(b)    Capital Structure.

(i)  The Parent.  As of the date hereof, the authorized capital stock of the
     Parent consists of 300,000,000 shares of Parent Common Stock, par value
     $.50 per share, and 5,000,000 shares of preferred stock, par value $.50 per
     share ("Parent Preferred Stock").  At the close of business on May 29,
     1998, (A) 122,341,004 shares of Parent Common Stock were issued and
     outstanding, all of which were validly issued, fully paid and
     nonassessable, and free of preemptive rights, (B) 850,328 shares of Parent
     Common Stock were held in the treasury of the Parent, and (C) 12,576,826
     shares of Parent Common Stock were reserved for future issuance pursuant to
     stock option arrangements of the Parent (collectively, the "Parent Stock
     Option Plans"), of which 3,512,826 shares were reserved for future issuance
     under stock options granted as of May 29, 1998.  The Parent Stock Option
     Plans are the only benefit plans of the Parent or its Subsidiaries under
     which any securities of the Parent or any of its Subsidiaries are issuable.
     No shares of Parent Preferred Stock are outstanding.  As of the date of
     this Agreement, except as set forth above, no shares of capital stock or
     other voting securities of the Parent were issued, reserved for issuance or
     outstanding.  As of the date of this Agreement, except for stock options
     covering not in excess of 3,512,826 shares of Parent Common Stock issued
     under the Parent Stock Option Plans (collectively, the "Parent Stock
     Options"), there are no options,

                                     A-32
<PAGE>
 
     warrants, calls, rights or agreements to which the Parent or any of its
     Subsidiaries is a party or by which any of them is bound obligating the
     Parent or any of its Subsidiaries to issue, deliver or sell, or cause to be
     issued, delivered or sold, additional shares of capital stock of the Parent
     or any of its Subsidiaries or obligating the Parent or any of its
     Subsidiaries to grant, extend or enter into any such option, warrant, call,
     right or agreement. Each outstanding share of capital stock of each
     Subsidiary of the Parent that is a corporation is duly authorized, validly
     issued, fully paid and nonassessable, and each such share is owned by the
     Parent or another Subsidiary of the Parent free and clear of all security
     interests, liens, claims, pledges, options, rights of first refusal,
     agreements, limitations on voting rights, charges and other encumbrances of
     any nature whatsoever. The Parent does not have any outstanding bonds,
     debentures, notes or other obligations the holders of which have the right
     to vote (or convertible into or exercisable for securities having the right
     to vote) with the stockholders of the Parent on any matter.

(ii) The Merger Subsidiary.  The Merger Subsidiary has, as of the date hereof,
     authorized capital stock consisting of 1,000 shares of Subsidiary Common
     Stock, of which 1,000 shares are issued and outstanding and owned by the
     Parent.  The Merger Subsidiary is a corporation duly organized, validly
     existing and in good standing under the laws of the State of Delaware.  All
     of the issued and outstanding shares of the Merger Subsidiary have been
     validly issued, are fully paid and nonassessable and are free of preemptive
     rights.  There are no outstanding rights, options, warrants, conversion
     rights or agreements for the purchase or acquisition from, or the sale or
     issuance by, the Merger Subsidiary of any shares of its capital stock,
     other than this Agreement.  Since its organization, the Merger Subsidiary
     has conducted no business activities, except such as are related to this
     Agreement and the performance of its obligations hereunder.

(c)  Authority.  On or prior to the date of this Agreement, the Board of
Directors of the Parent has declared the Merger advisable and fair to and in the
best interest of the Parent and its shareholders. The Parent has all requisite
corporate power and authority to enter into this Agreement and the Company
Option Agreement, to consummate the transactions contemplated by the Company
Option Agreement and to consummate the transactions contemplated hereby. The
execution and delivery of this Agreement and the Company Option Agreement by the
Parent and the consummation by the Parent of the transactions contemplated
hereby and thereby have been duly authorized by all necessary corporate action
on the

                                     A-33
<PAGE>
 
part of the Parent, subject, in the case of this Agreement, to the filing
of a Certificate of Merger as required by the DGCL. This Agreement and the
Company Option Agreement have been duly executed and delivered by the Parent and
(assuming the valid authorization, execution and delivery of this Agreement and
the Company Option Agreement by the Company and the validity and binding effect
of this Agreement and the Company Option Agreement on the Company) constitute
the valid and binding obligation of the Parent enforceable against the Parent in
accordance with their respective terms, except to the extent that enforceability
thereof may be limited by applicable bankruptcy, insolvency, reorganization or
other similar laws affecting the enforcement of creditors' rights generally and
by principles of equity regarding the availability of remedies. The issuance of
shares of Parent Common Stock to be issued in the Merger and the filing of a
registration statement on Form S-4 with the SEC by the Parent under the
Securities Act for the purpose of registering the shares of Parent Common Stock
to be issued in the Merger (together with any amendments or supplements thereto,
whether prior to or after the effective date thereof, the "Registration
Statement") have been duly authorized by the Parent's Board of Directors.

(d)  Consents and Approvals; No Violation.  Assuming that all consents, 
approvals, authorizations and other actions described in this Section 3.2(d)
have been obtained and all filings and obligations described in this Section
3.2(d) have been made, the execution and delivery of this Agreement and the
Company Option Agreement do not, and the consummation of the transactions
contemplated hereby and thereby and compliance with the provisions hereof and
thereof will not, result in any violation of, or default (with or without notice
or lapse of time, or both) under, or give to others a right of termination,
cancellation or acceleration of any obligation or the loss of a material benefit
under, or result in the creation of any lien, security interest, charge or
encumbrance upon any of the properties or assets of the Parent or any of its
Subsidiaries under, any provision of (i) the Articles of Incorporation or Bylaws
of the Parent, (ii) any provision of the comparable charter or organization
documents of any of the Parent's Subsidiaries, (iii) any loan or credit
agreement, note, bond, mortgage, indenture, lease or other agreement,
instrument, permit, concession, franchise or license applicable to the Parent or
any of its Subsidiaries, or (iv) any judgment, order, decree, statute, law,
ordinance, rule or regulation applicable to the Parent or any of its
Subsidiaries or any of their respective properties or assets, other than, in the
case of clauses (ii), (iii) or (iv), any such violations, defaults, rights,
liens, security interests, charges or encumbrances that, individually or in the
aggregate, would not have a Material Adverse Effect on the Parent, materially
impair the ability of the Parent to perform its obligations hereunder or under
the Company Option Agreement or prevent the consummation of any of the

                                     A-34
<PAGE>
 
transactions contemplated hereby or thereby. No filing or registration with, or
authorization, consent or approval of, any Governmental Entity is required by or
with respect to the Parent or any of its Subsidiaries in connection with the
execution and delivery of this Agreement or the Company Option Agreement by the
Parent or is necessary for the consummation of the Merger and the other
transactions contemplated by this Agreement or the Company Option Agreement,
except for (i) in connection, or in compliance, with the provisions of the HSR
Act, the Securities Act and the Exchange Act, (ii) the filing of the Certificate
of Merger with the Secretary of State of the State of Delaware, (iii) applicable
requirements, if any, of state securities or "blue sky" laws and the NYSE, (iv)
approval for listing the Parent Common Stock to be issued in the Merger on the
NYSE, and (v) such other consents, orders, authorizations, registrations,
declarations and filings the failure of which to be obtained or made would not,
individually or in the aggregate, have a Material Adverse Effect on the Parent,
materially impair the ability of the Parent to perform its obligations hereunder
or under the Company Option Agreement or prevent the consummation of any of the
transactions contemplated hereby or thereby.


(e) SEC Documents and Other Reports. The Parent has filed all required documents
with the SEC since January 1, 1995 (the "Parent SEC Documents"). As of their
respective dates, the Parent SEC Documents complied in all material respects
with the requirements of the Securities Act or the Exchange Act, as the case may
be, and, at the respective times they were filed, none of the Parent SEC
Documents contained any untrue statement of a material fact or omitted to state
a material fact required to be stated therein or necessary to make the
statements therein, in light of the circumstances under which they were made,
not misleading. The consolidated financial statements (including, in each case,
any notes thereto) of the Parent included in the Parent SEC Documents (the
"Parent Financial Statements") complied as to form in all material respects with
applicable accounting requirements and the published rules and regulations of
the SEC with respect thereto, were prepared in accordance with generally
accepted accounting principles (except, in the case of the unaudited statements,
as permitted by Form 10-Q of the SEC) applied on a consistent basis during the
periods involved (except as may be indicated therein or in the notes thereto)
and fairly presented in all material respects the consolidated financial
position of the Parent and its consolidated Subsidiaries as at the respective
dates thereof and the consolidated results of their operations and their
consolidated cash flows for the periods then ended. Except as disclosed in the
Parent SEC Documents or as required by generally accepted accounting principles,
the Parent has not, since March 31, 1998, made any change in the accounting
practices or policies applied in the preparation of the Parent Financial
Statements. Neither the

                                     A-35
<PAGE>
 
Parent nor any of its Subsidiaries had as of March 31, 1998 any liabilities or
obligations of any nature, whether or not accrued, contingent or otherwise, that
would be required by generally accepted accounting principles to be reflected on
the consolidated balance sheet of the Parent and its Subsidiaries (including the
notes thereto) included in the Financial Statements that are not so reflected.


(f)  Registration Statement and Prospectus/Proxy Statement.  None of
the information to be supplied by the Parent for inclusion or incorporation by
reference in the Registration Statement or the Prospectus/Proxy Statement will
(i) in the case of the Registration Statement, at the time it becomes effective,
contain any untrue statement of a material fact or omit to state any material
fact required to be stated therein or necessary in order to make the statements
therein not misleading or (ii) in the case of the Prospectus/Proxy Statement, at
the time of the mailing of the Prospectus/Proxy Statement, at the time of each
of the Stockholders Meeting and at the Effective Time, contain any untrue
statement of a material fact or omit to state any material fact required to be
stated therein or necessary in order to make the statements therein, in light of
the circumstances under which they are made, not misleading.  If at any time
prior to the Effective Time any event with respect to the Parent, its officers
and directors or any of its Subsidiaries shall occur which is required at that
time to be described in the Prospectus/Proxy Statement or the Registration
Statement, such event shall be so described, and an appropriate amendment or
supplement shall be promptly filed with the SEC and, as required by law,
disseminated to the stockholders of the Parent.  The Registration Statement will
comply (with respect to the Parent) as to form in all material respects with the
provisions of the Securities Act, and the Prospectus/Proxy Statement will comply
(with respect to the Parent) as to form in all material respects with the
provisions of the Exchange Act.

(g)  Absence of Certain Changes or Events.  Except as disclosed in the
Parent SEC Documents filed with the SEC prior to the date of this Agreement,
since March 31, 1998, there has been no event causing a Material Adverse Effect
on the Parent, or any development that would, individually or in the aggregate,
result in a Material Adverse Effect on the Parent.

(h)  Permits and Compliance. The Parent is in possession of all franchises, 
grants, authorizations, licenses, permits, easements, variances, exceptions,
consents, certificates, approvals and orders of any Governmental Entity
necessary for the Parent to own, lease and operate its properties or to carry on
its business as it is now being conducted (the "Parent Permits"), except where
the failure to have any of the Parent Permits would not, individually or in the
aggregate, have a Material Adverse Effect on the Parent, and, as of the date of
this Agreement, no suspension or cancellation of any of the

                                     A-36
<PAGE>
 
Parent Permits is pending or, to the knowledge of the Parent, threatened, except
where the suspension or cancellation of any of the Parent Permits would not,
individually or in the aggregate, have a Material Adverse Effect on the Parent.
Parent is not in violation of (i) its charter, by-laws or other organizational
documents, (ii) any applicable law, ordinance, administrative or governmental
rule or regulation, or (iii) any order, decree or judgment of any Governmental
Entity having jurisdiction over the Parent, except, in the case of clauses (i),
(ii) and (iii), for any violations that, individually or in the aggregate, would
not have a Material Adverse Effect on the Parent. As of the date hereof, there
is no contract or agreement, not entered into in the ordinary course of
business, that is material to the business, properties, assets, liabilities,
financial condition, results of operations or prospects of the Parent and its
Subsidiaries, taken as a whole. Except as set forth in the Parent SEC Documents
filed prior to the date of this Agreement, no event of default or event that,
but for the giving of notice or the lapse of time or both, would constitute an
event of default exists or, upon the consummation by the Parent of the
transactions contemplated by this Agreement or the Company Option Agreement,
will exist under any indenture, mortgage, loan agreement, note or other
agreement or instrument for borrowed money, any guarantee of any agreement or
instrument for borrowed money or any lease, contractual license or other
agreement or instrument to which the Parent is a party or by which the Parent is
bound or to which any of the properties, assets or operations of the Parent is
subject, other than any defaults that, individually or in the aggregate, would
not have a Material Adverse Effect on the Parent.

(i)  Actions and Proceedings.  Except as set forth in the Parent SEC
Documents filed prior to the date of this Agreement, there are no outstanding
orders, judgments, injunctions, awards or decrees of any Governmental Entity
against or involving the Parent or any of its Subsidiaries, or against or
involving any of the present or, to the knowledge of the Parent, former
directors, officers, employees, consultants or agents of the Parent or any of
its Subsidiaries, in their capacities as such, any of its or their properties,
assets or business or employee benefit plan of the Parent that, individually or
in the aggregate, would have a Material Adverse Effect on the Parent or
materially impair the ability of the Parent to perform its obligations hereunder
or under the Company Option Agreement.  As of the date of this Agreement, there
are no actions, suits, labor disputes or claims or legal, administrative or
arbitrative proceedings or governmental investigations pending or, to the
knowledge of the Parent, threatened against or involving the Parent or any of
its Subsidiaries or any of its or their present or, to the knowledge of the
Parent, former directors, officers, employees, consultants, agents or
stockholders, in their capacities as such, or any of its or their properties,

                                     A-37
<PAGE>
 
assets or business or any employee benefit plan of the Parent that, individually
or in the aggregate, would have a Material Adverse Effect on the Parent or
materially impair the ability of the Parent to perform its obligations hereunder
or under the Company Option Agreement.  As of the date hereof, there are no
actions, suits, labor disputes or other litigation, legal or administrative
proceedings or governmental investigations pending or, to the knowledge of the
Parent, threatened against or affecting the Parent or any of its Subsidiaries or
any of its or their present or, to the knowledge of the Parent, former officers,
directors, employees, consultants, agents or stockholders, in their capacities
as such, or any of its or their properties, assets or business relating to the
transactions contemplated by this Agreement and the Company Option Agreement.
For purposes of this Agreement, the term "knowledge of the Parent" shall mean
the actual knowledge of the officers and directors of the Parent.

(j)  FDA Matters.  Neither the Parent nor any of its Subsidiaries (i)
is a party to any pending investigation or proceeding by or before the FDA or
any other duly authorized Drug Regulatory Agencies or any other duly authorized
governmental authority which regulates the sale of drugs and controlled
substances in any jurisdiction; (ii) has knowledge of any pending regulatory
action of any sort (other than non-material routine or periodic inspections or
reviews) against the Parent or any of its Subsidiaries by the FDA or any other
duly authorized Drug Regulatory Agencies or any other governmental authority
which regulates the sale of drugs and controlled substances in any jurisdiction
which could have a Material Adverse Effect on the Parent, or in any material way
limit or restrict the ability of the Parent or any of its Subsidiaries to market
existing products; (iii) has knowingly committed or permitted to exist any
violation of the rules and regulations of the FDA or any other duly authorized
Drug Regulatory Agencies or any other governmental authority which regulates the
sale of drugs and controlled substances in any jurisdiction which has not been
cured by the Parent or any of its Subsidiaries or waived by the FDA or any such
regulatory authority; (iv) has received notice from any third party (whether or
not in writing), or has knowledge of, any claim, dispute or controversy relating
to the supply of regulated materials used in the products of the Parent or any
of its Subsidiaries, or the quality, formulation, potency, toxicity or efficacy
of such materials; or (v) anticipates, or knows of any pending, threatened or
potential action by any duly authorized Drug Regulatory Agencies or any other
governmental authority which regulates the sale of drugs and controlled
substances in any jurisdiction which could have a Material Adverse Effect on the
Parent or in any material way limit or restrict the ability of the Parent or any
of its Subsidiaries to market existing products.  To the knowledge of the
Parent, it and each of its Subsidiaries have

                                     A-38
<PAGE>
 
fulfilled in all material respects all regulatory requirements necessary or
requisite to the continued marketing of their existing products.


(k)  Labor Relations.   To the knowledge of the Parent, the Parent has a
good relationship with its employees and has no reason to believe that there
will be any adverse change in any such relationship, whether as a result of the
consummation of the transactions provided for by this Agreement or otherwise.


(l)  Patents and Certain Other Intellectual Property Rights.

(i)  The Parent owns, or possesses the right to use, all of the necessary
     intellectual property rights to the conduct of the business of the Parent
     as presently conducted except for rights to which, if not so owned or
     possessed, would not individually or in the aggregate have a Material
     Adverse Effect on the Parent.  Such ownership or right to use, as the case
     may be, is free and clear of all liens, security interests, claims and
     rights to use of third parties except those which would not, individually
     or in the aggregate have a Material Adverse Effect on the Parent.

(ii) There are no material royalties, honoraria, fees or other payments,
     incurred outside the ordinary course of business, payable as of the date
     hereof by the Parent to any person by reason of the ownership, use,
     license, sale or disposition of any of the Parent's intellectual property
     rights.

(iii)The Parent is not, to the knowledge of the Parent, infringing the right of
     any other party with respect to any intellectual property rights which
     would, individually or in the aggregate, be reasonably likely to have a
     Material Adverse Effect on the Parent.

(m) Parent Common Stock. The shares of Parent Common Stock to be issued in
accordance with this Agreement will be, upon issuance, duly authorized, validly
issued, fully paid and nonassessable, with no personal liability attaching to
the ownership thereof. Such issuance of shares of Parent Common Stock will be
free of any restrictions on transfer imposed by the Parent, other than those
contemplated by this Agreement. There are no preemptive rights or other anti-
dilution rights which would become effective upon or prohibit such issuance of
shares of Parent Common Stock.

(n)  Opinion of Financial Advisor.  The Parent has received the written
opinion of SBC Warburg Dillon Read Inc. ("Dillon Read"), dated the date hereof,
to the effect that, as of the date hereof, the Exchange Ratio is fair to the

                                     A-39
<PAGE>
 
Parent from a financial point of view, a copy of which opinion has been
delivered to the Company.

(o)  Finders and Investment Bankers.  Except for Dillon Read, whose
fees will be paid by the Parent, there is no investment banker, broker, finder
or other intermediary which has been retained by or is authorized to act on
behalf of the Parent or the Merger Subsidiary who might be entitled to any fee
or commission in connection with the transactions contemplated by this
Agreement.

(p)  Parent Affiliate Agreements.  Schedule 3.2(p) contains a list
                                   ---------------                
(reasonably satisfactory to counsel for the Company) identifying those Persons
who may be deemed to be "affiliates" of the Parent on the date hereof, as that
term is used in paragraphs (c) and (d) of Rule 145 under the Securities Act (the
"Parent Affiliates").

3.3         Representations and Warranties as to the Merger Subsidiary.
            ---------------------------------------------------------- 
          The Parent and the Merger Subsidiary represent and warrant to the
          Company as follows:

(a)  Organization, Standing, Power and Capitalization of the Merger
Subsidiary.  The Merger Subsidiary is a corporation duly organized, validly
existing and in good standing under the laws of the state of Delaware with all
requisite corporate power and authority to carry on the business to be conducted
by it prior to the Effective Date and to enter into this Agreement and perform
its obligations hereunder.  The Merger Subsidiary is not, and is not required to
be, qualified to do business in any jurisdiction other than the state of
Delaware.  The Merger Subsidiary has duly authorized capital stock consisting of
1,000 shares of common stock, par value $.50 per share, all of which are issued
and outstanding and owned by the Parent.  All of such issued and outstanding
shares have been validly issued, are fully paid and nonassessable, and are free
of preemptive rights.  There are no outstanding rights, options, warrants,
conversion rights or agreements for the purchase or acquisition from, or the
sale or issuance by, the Merger Subsidiary of any shares of its capital stock
other than in connection with this Agreement.

(b)  Business of the Merger Subsidiary.  Since its organization, the
Merger Subsidiary has not engaged in any business activities, entered into any
transactions or incurred any liabilities whatsoever, except such as are related
to the transactions contemplated by this Agreement.  The Merger Subsidiary has
no subsidiaries.

(c)  Authorization; Binding Agreement.  Pursuant to its Certificate of
Incorporation, the Merger Subsidiary has requisite corporate power and

                                     A-40
<PAGE>
 
authority to execute and deliver this Agreement and to consummate the
transactions contemplated hereby. The execution and delivery of this Agreement
and the consummation of the transactions contemplated hereby, including but not
limited to the Merger, have been duly and validly authorized by the Parent as
sole stockholder of the Merger Subsidiary and by the Merger Subsidiary's Board
of Directors and no other corporate proceedings on the part of the Merger
Subsidiary are necessary to authorize the execution and delivery of this
Agreement or to consummate the transactions so contemplated. This Agreement has
been duly and validly authorized, executed and delivered by the Merger
Subsidiary and constitutes the legal, valid and binding agreement of the Merger
Subsidiary, enforceable against it in accordance with its terms, except to the
extent that enforceability thereof may be limited by applicable bankruptcy,
insolvency, reorganization or other similar laws affecting the enforcement of
creditors' rights generally and by principles of equity regarding the
availability of remedies.

(d)  Compliance With Other Instruments, Etc.  Neither the execution or
delivery of this Agreement nor the consummation of the transactions contemplated
hereby will conflict with, result in any violation of or constitute a default
under the Certificate of Incorporation or Bylaws of the Merger Subsidiary or any
judgment, decree, order or any material law or regulation by which the Merger
Subsidiary is bound or affected.

(e)  Governmental and Other Consents, Etc.  No consent, approval or
authorization of or designation, declaration or filing with any Governmental
Entity on the part of the Merger Subsidiary is required in connection with the
execution or delivery of this Agreement by the Merger Subsidiary or the Merger
Subsidiary's consummation of the transactions contemplated hereby other than (i)
filings in the State of Delaware in accordance with the DGCL and (ii) filings
under the HSR Act.

4.          COVENANTS.
            --------- 
4.1         Covenants of the Company.
            ------------------------ 
          The Company agrees that prior to the Effective Date:

(a)  Action in Furtherance of Merger.  Subject to the terms and
conditions herein provided, the Company agrees to use commercially reasonable
efforts to take, or cause to be taken, such action, and to do, or cause to be
done, such things as are necessary, proper or advisable to consummate and make
effective as promptly as practicable the Merger and the transactions
contemplated by this Agreement, including (i) the defending of any lawsuits or
other legal proceedings, whether judicial or administrative,

                                     A-41
<PAGE>
 
challenging this Agreement or the consummation of the transactions contemplated
hereby, (ii) obtaining all governmental consents required for the consummation
of the Merger and the transactions contemplated thereby, and (iii) making all
necessary filings under the HSR Act. Upon the terms and subject to the
conditions hereof, the Company agrees to use commercially reasonable efforts to
take, or cause to be taken, such actions and to do, or cause to be done, such
things as are necessary to satisfy the other conditions of the Closing set forth
herein. The Company shall consult with counsel for the Parent as to, and shall
permit such counsel, at the Parent's expense, to participate in the decision-
making process as to the strategy to be employed in, any lawsuits or proceedings
referred to in clause (i) above brought against the Company, but not against the
Parent, provided that counsel for the Company shall retain control of any such
lawsuits or proceedings.

(b)  Maintenance of Properties.  The Company shall, and shall cause PL
to, maintain all of its and their respective properties in customary repair,
order and condition, reasonable wear and use and damage by fire or other
casualty excepted, and shall maintain, and shall cause PL to maintain, insurance
upon all of its and their properties and with respect to the conduct of its and
their businesses in amounts and kinds comparable to that in effect on the date
of this Agreement.

(c)  Access and Information.  Between the date of this Agreement and
the Effective Date, upon reasonable notice, the Company and PL shall give the
Parent and its authorized representatives (including its financial advisors,
accountants and legal counsel) access, at all reasonable times and in a manner
which shall not cause unreasonable disturbance, to all plants, offices,
warehouses and other facilities and to all contracts, agreements, commitments,
books and records (including Tax Returns) of the Company and PL (except to the
extent any such agreements or contracts by their terms restrict access to third
parties and the consent of the other party(ies) thereto cannot be obtained after
commercially reasonable efforts to do so), shall permit the Parent to make such
inspections as it may reasonably require and shall cause its officers and those
of PL promptly to furnish the Parent with such financial and operating data and
other information with respect to the business and properties of the Company and
PL, as may from time to time be reasonably requested.  All data and information
so received from the Company shall be deemed received pursuant to the
Confidentiality Agreement, and the Parent shall cause its officers, directors,
employees, auditors, counsel, financial advisors and agents to comply with the
provisions of the Confidentiality Agreement with respect to such data and
information.

                                     A-42
<PAGE>
 
(d)  Conduct of Business.  Except as expressly contemplated by this
Agreement or as otherwise agreed in writing by the Parent, during the period
from the date of this Agreement through the Effective Time, the Company shall,
and the Company shall cause PL to, conduct its business in the ordinary course
consistent with past practice, and the Company shall, and the Company shall
cause PL to, use commercially reasonable efforts to (i) preserve intact its
business organization, (ii) keep available the services of its officers and
employees, (iii) preserve its relationships with customers and suppliers, and
(iv) maintain satisfactory relationships with all other Persons with which it
does business.  Without limiting the generality of the foregoing, and except as
otherwise expressly provided in this Agreement or otherwise agreed to in writing
by the Parent, prior to the Effective Time, neither the Company nor PL shall,
without the prior written consent of the Parent:

(i)  amend or propose to amend its Certificate of Incorporation or Bylaws;

(ii) other than in the ordinary course of business consistent with past
     practice:  (A) create, incur or assume any indebtedness for borrowed money
     or obligations in respect of capital leases; (B) assume, guarantee, endorse
     or otherwise become liable or responsible (whether directly, indirectly,
     contingently or otherwise) for the obligations of any other Person except
     the Company or PL; (C) make any loans, advances or capital contributions
     to, or investments in, any other Person (other than customary travel or
     business advances to employees  made in the ordinary course of business
     consistent with past practice); (D) make any capital expenditure or
     expenditures which, individually, is in excess of $10,000 or, in the
     aggregate, are in excess of $50,000; (E) enter into or amend any agreement
     or contract material to the Company; or (F) incur any material liability or
     obligation (absolute, accrued, contingent or otherwise);

(iii)sell, transfer, lease, license or otherwise dispose of, or mortgage
     or encumber, or agree to sell, transfer, lease, license or otherwise
     dispose of, or mortgage or encumber, any assets or properties, real,
     personal, intangible or mixed, other than the sale, transfer or disposition
     of the Company's products in the ordinary course of business;

(iv) in the case of the Company, except as expressly provided in this Agreement,
     amend or terminate the Company Rights Plan prior to the earlier of the
     Effective Time or the termination of this

                                     A-43
<PAGE>
 
     Agreement, unless required to do so by a court of competent jurisdiction;

(v)  in the case of the Company, deliver any "put notices" under the Common
     Stock Investment Agreement or issue any shares of Company Common Stock
     pursuant thereto; or

(vi) authorize, recommend, propose or announce an intention to do any of the
     foregoing, or enter into any contract, agreement, commitment or arrangement
     to do any of the foregoing.

(e)  Capital Stock.  Between the date hereof and the Effective Time,
except as specifically contemplated by this Agreement or the Company Option
Agreement, neither the Company nor PL shall, unless otherwise agreed to in
writing by Parent, (i) make any changes in its authorized capital stock; (ii)
authorize or issue any securities convertible into, or exchangeable with, the
capital stock of the Company or PL; (iii) issue any stock options, warrants or
other rights calling for the issue, transfer, sale or delivery of its capital
stock or other securities except pursuant to the Company Stock Option Plans, the
Company Employee Stock Purchase Plan or the Company 401(k) Plan consistent with
past practice; provided, however, the Company shall not issue any "performance
share awards" and "stock purchase rights" under the Equity Incentive Plan of the
Company; (iv) declare or pay any stock dividend or effect any recapitalization,
split-up, combination, exchange of shares or other reclassification in respect
of its outstanding shares of capital stock; (v) issue, transfer, sell or deliver
any shares of its capital stock, except Company Common Stock to be issued:  (A)
upon the exercise of stock options previously granted pursuant to existing
Company Stock Option Plans or granted in accordance with this Section 4.1(e),
(B) pursuant to the exercise of the Company Warrant, or (C) as required by the
terms of the Company Employee Stock Purchase Plan or the Company 401(k) Plan;
(vi) purchase, redeem or otherwise acquire any outstanding shares of its capital
stock or any other securities of the Company or any rights, warrants or options
to acquire any such shares or securities; or (vii) declare, pay or set apart for
payment any dividends on, or make any other actual, constructive or deemed
distributions in respect of its capital stock or otherwise make any payments to
its stockholders in their capacity as such.  Except in a manner consistent with
past practice, no award or grant under the Company Stock Option Plans or any
other benefit plan or program shall be made without the consent of the Parent.
Except as specifically contemplated by this Agreement, the Company shall not
make any material amendment to any of (i) the Company Stock Option Plans or
options outstanding thereunder, or (ii) any other option or warrant agreement,
including, without limitation, the Company Warrant.

                                     A-44
<PAGE>
 
(f)  No Solicitation.

(i)  The Company shall cease, and shall cause PL to cease and shall use
     commercially reasonable efforts to cause its and PL's respective officers,
     directors, employees, counsel, investment bankers, financial advisers,
     accountants, other representatives and agents (collectively, the "Company
     Representatives") to cease, in each case immediately after the date hereof,
     any discussions or negotiations with any parties that may be ongoing with
     respect to a Takeover Proposal.  Neither the Company nor the Board of
     Directors of the Company shall, nor shall either of them authorize or
     permit PL or any Company Representative to:  (A) solicit, initiate or
     encourage (including by way of furnishing information), or take any other
     action to facilitate, any inquiries or the making of any proposal which
     constitutes, or may reasonably be expected to lead to, any Takeover
     Proposal; (B) participate in any discussion or negotiations regarding any
     Takeover Proposal; (C) approve or agree to or endorse any Takeover
     Proposal; (D) enter into any agreement with respect to any Takeover
     Proposal; or (E) other than as permitted by Section 4.1(m), withdraw or
     modify, or propose to withdraw or modify in a manner adverse to Parent, the
     approval or recommendation of this Agreement or the Merger; provided,
     however, that, notwithstanding any other provision hereof, the Company and
     the Board of Directors of the Company may, at any time prior to the time
     the stockholders of the Company shall have approved the Merger, engage in
     the actions prohibited by this Section 4.1(f)(i) in response to an
     unsolicited Takeover Proposal which did not result from a breach of this
     Section 4.1(f)(i) and subject to compliance with Section 4.1(f)(ii) if, and
     only to the extent that, (x) the Board of Directors of the Company
     determines in good faith, based upon the advice of its legal counsel as to
     legal matters, that it is necessary to do so in order to comply with its
     fiduciary duties to the Company's shareholders under applicable law, (y)
     the Board of Directors of the Company determines that the Takeover Proposal
     is a Superior Proposal, and (z) the party who submitted the Takeover
     Proposal executes a customary confidentiality agreement (as determined by
     the Company after receiving such Takeover Proposal and after consultation
     with its outside legal counsel), the benefits of the terms of which if more
     favorable to the other party than those contained in the confidentiality
     agreement in place with Parent, shall be extended to Parent,

(ii) In addition to the obligations of the Company set forth in Section
     4.1(f)(i), the Company shall promptly advise Parent orally and in

                                     A-45
<PAGE>
 
     writing of any Takeover Proposal received by Company or any request for
     information stated by the proponent to be in contemplation of any Takeover
     Proposal, or any inquiry which could reasonably be expected to lead to any
     Takeover Proposal, the material terms and conditions of such Takeover
     Proposal or request or inquiry and the identity of the Person making such
     Takeover Proposal, request or inquiry. The Company shall keep the Parent
     reasonably informed of any material amendment or modification to such
     Takeover Proposal, request or inquiry.


(iii) "Takeover Proposal" means any inquiry, proposal or offer from any
      Person relating to any: (A) tender or exchange offer, merger,
      consolidation or similar transaction involving the Company or PL, (B)
      sale, lease or other disposition directly or indirectly by merger,
      consolidation, or share exchange of assets of the Company or PL
      representing 10% or more of the consolidated assets of the Company or PL,
      (C) issuance, sale or other disposition of (including by way of merger,
      consolidation, share exchange or similar transaction) securities (or
      options, rights or warrants to purchase, or securities convertible into,
      such securities) representing 10% or more of the voting power of the
      Company, (D) transaction in which any Person shall acquire beneficial
      ownership (as such term is defined in Rule 13d-3 under the Exchange Act),
      or the right to acquire beneficial ownership or any "group" (as such term
      is defined under the Exchange Act) shall have been formed which
      beneficially owns or has the right to acquire beneficial ownership of 25%
      or more of the outstanding Common Stock, in each case, other than the
      transactions with Parent contemplated by this Agreement or the Company
      Option Agreement referred to in the recitals to this Agreement.

(iv) "Superior Proposal" means any Takeover Proposal on terms which the Board of
     Directors of the Company determines in its good-faith judgment, based in
     part on the advice of a financial advisor of nationally recognized
     reputation (which opinion shall be provided promptly to Parent), to be more
     favorable to the stockholders of the Company than the Merger from a
     financial point of view and for which financing is then committed or
     reasonably likely to be available.

(v)  For purposes of this Agreement, the term "Person" shall mean any
     individual, corporation, partnership, trust, unincorporated association,
     limited liability company, governmental agency or any other entity.

                                     A-46
<PAGE>
 
(g)  No Final Put Notice.  The Company shall refrain from delivering a
"final put notice" in respect of the "put notice" delivered under the Common
Stock Investment Agreement on June 4, 1998.

(h)  Compensation Matters.  Except with the prior written consent of
the Parent, neither the Company nor PL shall (i) pay, agree to pay or accelerate
the payment of any bonus, severance or other compensation to any officer or
employee not currently required under an existing agreement or employee benefit
plan or arrangement (and with respect to officers and directors, only to the
extent such agreement, plan or arrangement is described in the Company's 1998
Proxy Statement) except for increases in compensation of employees who are not
officers or directors of the Company consistent with past practices, (ii) make
payment of any bonus, severance or other compensation to any officer or employee
which is permitted hereunder in any property other than cash, (iii) create any
new employee benefit plan or arrangement, (iv) modify any existing employee
benefit plan, arrangement or agreement in any respect which would materially
increase the compensation payable thereunder to employees, or (v) enter into any
new employment agreement or modify any existing employment agreement of any
employee who is an officer or director of the Company or PL.

(i)  Contracts.  Except as otherwise agreed to in writing by the
Parent, neither the Company nor PL shall enter into, terminate or modify in any
material respect any contract, agreement or commitment material to the Company
without the prior written consent of the Parent, which consent shall not be
unreasonably withheld.

(j)  Tax Matters.  The Company and PL shall continue to file when due
all federal, state, local, foreign and other tax returns, reports and
declarations required to be filed by them, and shall pay or make full and
adequate provision for the payment of all taxes and governmental charges due or
payable by them.  Neither the Company nor PL shall prepare or file any Tax
Return inconsistent with past practice or, on any such Tax Return, take any
position, make any election, or adopt any method that is inconsistent with
positions taken, elections made or methods used in preparing or filing similar
Tax Returns in prior periods or make any tax election or settle or compromise
any material federal, state, local or foreign income tax liability.

(k)  Amendments to the Schedules.  The Company shall make such
amendments to the Schedules referred to in Section 3.1 as are necessary to
reflect therein the occurrence of events or transactions occurring after the
date hereof and shall deliver a copy of each such amendment to the Parent on the
same date as the date of the amendment.  The Company shall

                                     A-47
<PAGE>
 
deliver such additional amendments from time to time as are necessary to reflect
any material event occurring between the date hereof and the Effective Date.

(l)  Notification of Certain Matters.  The Company shall give prompt
notice to the Parent of:  (i) any notice of, or other communication relating to,
a default or event which, with notice or lapse of time or both, would become a
default under any agreement, indenture or instrument to which the Company or PL
is a party or is subject which default could reasonably be expected to have a
Material Adverse Effect on the Company; (ii) any notice or other communication
from any third party alleging that the consent of such third party is or may be
required in connection with the transactions contemplated by this Agreement
including the Merger; (iii) any notice or other communication from any
regulatory authority or national securities exchange in connection with the
transactions contemplated by this Agreement; (iv) any Material Adverse Change
suffered by the Company, or the occurrence of an event which would be reasonably
expected to have a Material Adverse Effect on the Company; and (v) any claims,
actions, proceedings or investigations commenced or threatened in writing
involving or affecting the Company or PL, or any of their respective property or
assets, or any employee, consultant, director or officer, in his or her capacity
as such, of the Company or PL, which, if pending on the date hereof, would have
been required to have been disclosed pursuant to this Agreement or which relates
to the consummation of the Merger.

(m)  Stockholder Approval.  The Company shall take all steps necessary
to duly call, give notice of, convene and hold, no later than thirty-five (35)
days after the Registration Statement has been declared effective by the SEC, a
special meeting of its stockholders in accordance with the DGCL to consider and
vote upon the adoption and approval of this Agreement and the Merger and the
transactions contemplated hereby (the "Stockholders Meeting").  The Company,
through its Board of Directors, shall adopt a recommendation to the stockholders
of the Company that they adopt and approve this Agreement, shall use
commercially reasonable efforts, consistent with its legal obligations, to
obtain any necessary approval by its stockholders of the transactions
contemplated hereby and shall not withdraw or modify such recommendation, except
as permitted by Section 4.1(f)(i) or on the basis of the occurrence of a
Material Adverse Change with respect to the Parent or the occurrence of an event
which has, or can reasonably be expected to have, a Material Adverse Effect on
the Parent and the Board of Directors of the Company determines in good faith,
based upon the advice of its counsel as to legal matters, that it is necessary
to do so in order to comply with its fiduciary duties to the Company's
stockholders under applicable law.  Without limiting the

                                     A-48
<PAGE>
 
generality of the foregoing, the Company agrees that its obligations pursuant to
the first sentence of this Section 4.1(m) shall not be affected by the
commencement, public proposal, public disclosure or communication to the Company
of a Takeover Proposal.

(n)  Financial Statements.  The Company, promptly after the preparation
thereof, shall send to the Parent any financial statements prepared by or on
behalf of it for periods subsequent to March 31, 1998 as to which the
representations and warranties regarding the Company Financial Statements set
forth in Section 3.1(e) shall apply.

(o)  Proxy Statement.  The Company shall deliver to the Parent the
final form of proxy statement which the Company intends to distribute to its
stockholders in connection with the adoption and approval of this Agreement and
the Merger.

(p)  Company Affiliates.  The Company shall deliver to the Parent an
updated Schedule 3.1(s) reflecting any change in the identity of the Company
        ---------------                                                     
Affiliates within five (5) days of the Company having knowledge of such change.
In the event additional Persons become Company Affiliates after the date hereof,
the Company shall use commercially reasonable efforts to cause each such Person
to deliver to the Parent a written agreement in substantially the form of
Exhibit C hereto with each such Person within ten (10) days after the Company
- ---------                                                                    
has knowledge that such Person has become a Company Affiliate.

(q)  Takeover Statutes.  If any "business combination," "fair price,"
"control share acquisition" or "moratorium" statute or other similar statute or
regulation or any state "blue sky" or securities law statute shall become
applicable to the transactions contemplated hereby, the Company and the Board of
Directors of the Company shall, to the extent consistent with applicable law,
grant such approvals and take such actions as are reasonably necessary so that
the transactions contemplated hereby and thereby may be consummated as promptly
as practicable on the terms contemplated hereby and otherwise act to minimize
the effects of such statute or regulations on the transactions contemplated
hereby.

(r)  Prohibited Transactions.  The Company shall not acquire or agree
to acquire by merging or consolidating with, or by purchasing a substantial
portion of the assets of or equity in, or by any other manner, any business or
any corporation, limited liability company, partnership, association or other
business organization or division thereof or otherwise acquire or agree to
acquire any assets, other than transactions that are in the ordinary course of
business consistent with past practice and not material to the Company and PL
taken as a whole.  The Company shall not alter (through

                                     A-49
<PAGE>
 
merger, liquidation, reorganization, restructuring or in any other fashion) the
corporate structure or ownership of the Company or PL.

(s)  Accounting Changes.  The Company shall not make any change to
accounting policies or procedures (other than actions required to be taken by
generally accepted accounting principles).

(t)  Compliance With Law.  The Company shall not knowingly violate or
knowingly fail to perform any obligation or duty imposed upon it or PL by any
applicable federal or state law or regulation, guideline or ordinance.

(u)  Company Affiliates Agreements.  The Company shall use commercially
reasonable efforts to cause each Company Affiliate to deliver to the Parent
within ten (10) days of the date hereof a written agreement in substantially the
form of Exhibit C hereto, executed by each such Person.
        ---------                                      

4.2         Covenants of the Parent.
            ----------------------- 
          The Parent agrees that prior to the Effective Date:

(a)  Action in Furtherance of Merger.  Subject to the terms and
conditions herein provided, the Parent agrees to use commercially reasonable
efforts to take, or cause to be taken, such actions, and to do, or cause to be
done, such things as are necessary, proper or advisable to consummate and make
effective as promptly as practicable the Merger and the transactions
contemplated by this Agreement, including (i) defending any lawsuits or other
legal proceedings, whether judicial or administrative, challenging this
Agreement or the consummation of the transactions contemplated hereby, (ii)
obtaining all governmental consents required for the consummation of the Merger
and the transactions contemplated thereby, (iii) making all necessary filings
under the HSR Act, (iv) filing the Registration Statement and causing the same
to become effective; and (v) to the extent that the shares of Company Common
Stock are not voted in accordance with the terms of the Voting Agreements,
voting the irrevocable proxies granted to the Parent in the Voting Agreements in
favor of approving this Agreement and the transactions contemplated hereby, all
on the terms and conditions provided for herein.  Upon the terms and subject to
the conditions hereof, the Parent agrees to use commercially reasonable efforts
to take, or cause to be taken, such actions and to do, or cause to be done, such
things as are necessary to satisfy the other conditions of the Closing set forth
herein.  The Parent shall consult with counsel for the Company as to, and shall
permit such counsel, at the Company's expense, to participate in the decision-
making process as to the strategy to be employed in any lawsuits or proceedings
referred to in clause (i) above (which shall not include any such lawsuits or
proceedings to the extent that they relate to the Registration Statement)
brought against

                                     A-50
<PAGE>
 
the Parent, but not against the Company, provided that counsel for the Parent
shall retain control of any such lawsuits or proceedings. In case at any time
after the Effective Date any further action is necessary or desirable to carry
out the purposes of this Agreement, the officers and directors of the Surviving
Corporation shall take such necessary action and the Parent shall cause them to
do so.


(b)  Maintenance of Properties.  The Parent shall, and shall cause each
of its Subsidiaries to, maintain all of its and their respective properties in
customary repair, order and condition, reasonable wear and use and damage by
fire or other casualty excepted, and shall maintain, and shall cause each of its
Subsidiaries to maintain, insurance upon all of its and their properties and
with respect to the conduct of its and their businesses in amounts and kinds
comparable to that in effect on the date of this Agreement.

(c)  Access and Information.  Between the date of this Agreement and
the Effective Date, upon reasonable notice, the Parent shall give the Company
and its authorized representatives (including its financial advisors,
accountants and legal counsel) access, at all reasonable times and in a manner
which shall not cause unreasonable disturbance, to officers and senior
executives of the Parent as well as to financial and operating data and other
information as may from time to time be reasonably requested by the Company.
All data and information so received from the Parent shall be deemed received
pursuant to the Reciprocal Confidentiality Agreement, and the Company shall
cause its officers, directors, employees, auditors, counsel, financial advisors
and agents to comply with the provisions of the Reciprocal Confidentiality
Agreement with respect to such data and information.
 
(d)  Listing Application.  The Parent shall use commercially reasonable
efforts to effect listing of the Parent Common Stock to be delivered in
accordance with this Agreement on the NYSE upon notice of issuance.

(e)  Public Filings.  The Parent shall promptly file all periodic
reports required to be filed with the SEC and provide the Company with a copy of
such reports promptly after such filing.

(f)  Registration Statement.  The Parent shall deliver to the Company
the final form of Registration Statement which the Parent intends to have
declared effective by the SEC.

(g)  Conduct of Business.  Except as expressly contemplated by this
Agreement, during the period from the date of this Agreement to the Effective
Date, the Parent shall, and the Parent shall cause each of its

                                     A-51
<PAGE>
 
Subsidiaries to, conduct its business in the ordinary course and consistent with
past practice.


4.3         Covenants as to the Merger Subsidiary.
            ------------------------------------- 
          The Parent and the Merger Subsidiary agree that prior to the Effective
          Date:

(a)  No Business.  The Merger Subsidiary shall not engage in any
business activities or enter into any transaction whatsoever, except such as are
related to this Agreement and the performance of its obligations hereunder.

(b)  Access.  Until the Effective Date or until the abandonment of the
Merger as permitted by this Agreement, the Merger Subsidiary shall give to the
Company and its representatives full access, during normal business hours and
upon reasonable notice, to all of its properties, books, contracts, documents
and records, and shall furnish to the Company such financial and other
information concerning the Merger Subsidiary as the Company and its
representatives may from time to time reasonably request.

(c)  Actions in Furtherance of Merger.  The Merger Subsidiary shall use
commercially reasonable efforts to obtain such consents and authorizations of
third parties, to make such filings, and to give such notices to third parties,
which may be necessary or reasonably required on the part of the Merger
Subsidiary in order to effect, or in connection with, the transactions
contemplated by this Agreement.

4.4         Covenants of the Company and the Parent.
            --------------------------------------- 

(a)  Registration Statement.  The Company shall cooperate with the
Parent in the preparation by the Parent of, and the Parent shall file, the
Registration Statement with the SEC and shall use commercially reasonable
efforts to cause it to become effective.  The Parent shall use commercially
reasonable efforts to qualify such securities, if required, under applicable
state securities laws and to cause the shares of Parent Common Stock which are
to be delivered pursuant to this Agreement to be listed on the NYSE.  The
Prospectus/Proxy Statement shall include the prospectus which forms a part of
the Registration Statement.  The obligations of the Company pursuant to this
Section 4.4 shall be limited to providing the information required by items 15
and 18 of Form S-4, and the expense of providing such information shall be borne
by the Company.

(b)  Tax-Free Reorganization Treatment.  Each of the Company and the
Parent shall use commercially reasonable efforts to cause the Merger to be
treated as a "reorganization" within the meaning of Section 368 of the Code.

                                     A-52
<PAGE>
 
5.          CONDITIONS TO CLOSING; ABANDONMENT AND TERMINATION.
            -------------------------------------------------- 
5.1         Conditions to Each Party's Obligation to Effect the Merger.
            ---------------------------------------------------------- 

          The respective obligations of each party to this Agreement to effect
          the Merger shall be subject to the satisfaction prior to the Effective
          Date of the following conditions, and the Company or the Parent shall
          (x) not be required to close the Merger if any of the following shall
          not be true or shall not have occurred and (y) have the right to
          abandon the Merger and terminate this Agreement if any of the
          following shall not be true or shall not have occurred, as the case
          may be, by 5:00 p.m., Eastern time, on November 30, 1998:

(a)  Company Stockholder Approval.  This Agreement and the Merger shall
have been approved and adopted by the affirmative vote of at least a majority of
the votes cast by holders of the Company Common Stock entitled to vote thereon.

(b)  Consents.  Except to the extent such consents are not required at
the Effective Date:  (i) the Company shall have received the consents or
exemptions, or made the filings, as the case may be, which are referred to in
Section 3.1(d); (ii) the Parent shall have received the consents or exemptions,
or made the filings, as the case may be, which are referred to in Section 3.2(d)
hereof; and (iii) all notification and report forms required to be filed on
behalf of the parties to this Agreement with the Federal Trade Commission and
the Department of Justice under the HSR Act and rules thereunder shall have been
filed, and the waiting period required to expire under the HSR Act and rules
thereunder, including any extension thereof, shall have expired or early
termination of the waiting period shall have been granted.

(c)  Effectiveness.  The Registration Statement shall have become
effective under the Securities Act and shall not be the subject of any stop
order or proceeding seeking a stop order.

(d)  Listing.  The Parent Common Stock to be issued in the Merger shall
have been approved for listing on the NYSE upon notice of issuance.

(e)  No Legal Restraints.  No temporary restraining order, preliminary
or permanent injunction or other order issued by a court of competent
jurisdiction or other legal restraint or prohibition preventing the consummation
of the Merger shall be in effect.

5.2         Conditions to the Company's Closing and Its Right to Abandon.
            ------------------------------------------------------------ 

          The Company shall (x) not be required to close the Merger if any of
          the following shall not be true or shall not have occurred or shall
          not have been waived in

                                     A-53
<PAGE>
 
          writing by the Company at the Closing and (y) have the right to
          abandon the Merger and terminate this Agreement if any of the
          following shall not be true or shall not have occurred, or shall not
          have been waived in writing by the Company, as the case may be, by
          5:00 p.m., Eastern time, on November 30, 1998:

(a)  No Material Adverse Effect.  No event or circumstance shall have
occurred which has, or is reasonably expected to have, a Material Adverse Effect
on the Parent, including, without limitation, any Material Adverse Effect caused
by any of the following:

(i)  The failure of the representations and warranties of the Parent and Merger
     Subsidiary herein contained to be true and correct in all respects on and
     as of the Effective Date with the same force and effect as though made on
     and as of the Effective Date except as affected by transactions
     specifically contemplated by this Agreement;

(ii) The failure of either the Parent or the Merger Subsidiary to have performed
     all its obligations and agreements and complied with all covenants
     contained in this Agreement to be performed and complied with by it on or
     prior to the Effective Date; and

(iii)The execution, delivery and performance by the Parent of this
     Agreement and the consummation of the Merger having, directly or
     indirectly, resulted in a breach of, constituted an event of default under
     or resulted in the acceleration of, with or without the giving of notice,
     lapse of time or both, an obligation under any agreement of the Parent.

(b)  No Material Adverse Change.  Between the date hereof and the
Effective Date, there shall have been no Material Adverse Change with respect to
the Parent.

(c)  Officer's Certificate.  The Company shall have received a
certificate of the Chairman of the Board, the President or any Vice-President of
each of the Parent and the Merger Subsidiary, dated the Effective Date,
certifying as to the absence of any of the matters mentioned in Sections 5.2(a)
and (b).

(d)  Tax Opinion.  The Company shall have received an opinion of Heller
Ehrman White & McAuliffe, in form and substance reasonably satisfactory to the
Company, dated the Effective Time, substantially to the effect that on the basis
of facts, representations and assumptions set forth in such opinion which are
consistent with the state of facts existing as of the Effective Time, for
federal income tax purposes:

                                     A-54
<PAGE>
 
(i)  the Merger shall constitute a "reorganization" within the meaning of
     Section 368(a) of the Code, and the Company, the Merger Subsidiary and the
     Parent shall each be a party to that reorganization within the meaning of
     Section 368(b) of the Code;

(ii) no gain or loss shall be recognized by the Parent, the Merger Subsidiary or
     the Company as a result of the Merger;

(iii)no gain or loss shall be recognized by stockholders of the Company
     who exchange their shares of Company Common Stock solely for shares of
     Parent Common Stock pursuant to the Merger, except to the extent of cash,
     if any, received in lieu of fractional shares of Parent Common Stock;

(iv) the aggregate tax basis of the shares of Parent Common Stock received in
     exchange for shares of Company Common Stock pursuant to the Merger
     (including any fractional share of Parent Common Stock deemed to have been
     received) shall be the same as the aggregate tax basis of such shares of
     Company Common Stock surrendered in exchange therefor;

(v)  the holding period for shares of Parent Common Stock received in exchange
     for shares of Company Common Stock pursuant to the Merger shall include the
     holder's holding period for such shares of Company Common Stock surrendered
     in exchange therefor, provided such shares of Company Common Stock were
     held as capital assets by the holder at the Effective Time; and

(vi) the receipt of cash in lieu of a fractional share of Parent Common Stock by
     a stockholder of the Company will be treated as if the fractional share
     were distributed as part of the exchange and then redeemed by the Parent,
     and the cash payment will be treated as having been received as a
     distribution in full payment in exchange for the fractional shares redeemed
     and taxed as provided in Section 302(a) of the Code.

In rendering such opinion, Heller Ehrman White & McAuliffe may rely as to
matters of fact upon the representations contained herein and may require and
rely upon representations from the Parent, the Company and others.

(e)  Tax Certificate.  The Parent shall have delivered to the Company a
certificate confirming the accuracy of the representations and warranties and
the performance of the covenants on the part of the Parent and the Merger
Subsidiary as set forth in Section 8.4(a) hereof.

                                     A-55
<PAGE>
 
5.3         Conditions to the Parent's and the Merger Subsidiary's Closing and
            ------------------------------------------------------------------
            Right of the Parent and the Merger Subsidiary to Abandon.
            -------------------------------------------------------- 

          The Parent and Merger Subsidiary shall (x) not be required to close
          the Merger if any of the following shall not be true or shall not have
          occurred or shall not have been waived in writing by the Parent at the
          Closing and (y) have the right to abandon the Merger and terminate
          this Agreement if any of the following shall not be true or shall not
          have occurred, or shall not have been waived in writing by the Parent,
          as the case may be, by 5:00 p.m., Eastern time, on November 30, 1998:

(a)  No Material Adverse Effect.  No event or circumstance shall have
occurred which has, or is reasonably expected to have, a Material Adverse Effect
on the Company, including, without limitation, any Material Adverse Effect
caused by any of the following:

(i)  The failure of the representations and warranties of the Company herein
     contained to be true and correct in all respects on and as of the Effective
     Date;

(ii) The failure of the Disclosure Schedules, as amended immediately prior to,
     but on the same day as, the Merger on the Effective Date for events or
     transactions occurring after the date of this Agreement, to be true and
     correct in all respects on and as of the Effective Date with the same force
     and effect as though made on and as of the Effective Date;

(iii)The disclosure by any amendment to the Disclosure Schedules of the
     existence of any adverse change in the business, assets, financial
     condition or the results of operation of the Company and PL, taken as a
     whole;

(iv) The failure of the Company to have performed all its obligations and
     agreements and complied with all covenants contained in this Agreement to
     be performed and complied with by it on or prior to the Effective Date; and

(v)  The execution, delivery and performance by the Company of this Agreement
     and the consummation of the Merger having, directly or indirectly, resulted
     in a breach of, constituted an event of default under or resulted in the
     acceleration of, with or without the giving of notice, lapse of time, or
     both, an obligation under any agreement of the Company.

                                     A-56
<PAGE>
 
(b)  No Material Adverse Change.  Between the date hereof and the
Effective Date, there shall have been no Material Adverse Change with respect to
the Company.

(c)  Officer's Certificate.  The Parent and the Merger Subsidiary shall
have received a certificate of the Chairman of the Board, the President or any
Vice-President of the Company, dated the Effective Date, certifying as to:

(i)  the absence of any of the matters mentioned in Sections 5.3(a) and (b);

(ii) the number of shares of Company Preferred Stock issued and outstanding;

(iii)the number of Outstanding Shares of Company Common Stock; and

(iv) the information relating to the Company supplied by the Company in writing
     specifically for inclusion in the Registration Statement.

(d)  Tax Opinion.  The Parent shall have received an opinion of
Buchanan Ingersoll Professional Corporation, in form and substance reasonably
satisfactory to the Parent, dated the Effective Date, substantially to the
effect that on the basis of facts, representations and assumptions set forth in
such opinion which are consistent with the state of facts existing as of the
Effective Time, for federal income tax purposes:

(i)  the Merger shall constitute a "reorganization" within the meaning of
     Section 368(a) of the Code, and the Company, the Merger Subsidiary and the
     Parent shall each be a party to that reorganization within the meaning of
     Section 368(b) of the Code;

(ii) no gain or loss shall be recognized by the Parent, the Merger Subsidiary or
     the Company as a result of the Merger;

(iii)no gain or loss shall be recognized by stockholders of the Company
     who exchange their shares of Company Common Stock solely for shares of
     Parent Common Stock pursuant to the Merger, except to the extent of cash,
     if any, received in lieu of fractional shares of Parent Common Stock;

(iv) the aggregate tax basis of the shares of Parent Common Stock received in
     exchange for shares of Company Common Stock pursuant to the Merger
     (including any fractional share of Parent Common Stock deemed to have been
     received) shall be the same

                                     A-57
<PAGE>
 
     as the aggregate tax basis of such shares of Company Common Stock
     surrendered in exchange therefor;

(v)  the holding period of the shares of Parent Common Stock received in
     exchange for shares of Company Common Stock pursuant to the Merger shall
     include the holder's holding period for such shares of Company Common Stock
     surrendered in exchange therefor, provided such shares of Company Common
     Stock were held as capital assets by the holder at the Effective Time; and

(vi) the receipt of cash in lieu of a fractional share of Parent Common Stock by
     a stockholder of the Company will be treated as if the fractional share
     were distributed as part of the exchange and then redeemed by the Parent,
     and the cash payment will be treated as having been received as a
     distribution in full payment in exchange for the fractional shares redeemed
     and taxed as provided in Section 302(a) of the Code.

In rendering such opinion, Buchanan Ingersoll Professional Corporation may rely
as to matters of fact upon the representations contained herein and may require
and rely upon representations from the Parent, the Company and others.


(e)  Tax Certificate.  The Company shall have delivered to the Parent a
certificate confirming the accuracy of the representations and warranties and
the performance of the covenants on the part of the Company and the Surviving
Corporation as set forth in Section 8.4(b) hereof.

(f)  Outstanding Shares of Preferred Stock.  No shares of the Company
Preferred Stock shall be issued or outstanding.

(g)  FIRPTA Statement.  The Company shall have delivered to the Parent
a statement that the interest in Company is not a United States real property
interest as contemplated by Section 1.1445-2(c)(3) of the regulations
promulgated under the Code.

6.          ADDITIONAL PROVISIONS FOR ABANDONMENT AND TERMINATION.
            ----------------------------------------------------- 
6.1         Provisions of Abandonment and Termination.
            ----------------------------------------- 

          In addition to the provisions of Article 5 hereof, the Merger may be
          abandoned and this Agreement may be terminated at any time on or
          before the Effective Time, whether before or after approval by the
          stockholders of the Company:

                                     A-58
<PAGE>
 
(a)  Mutual Agreement.  By mutual agreement of the Boards of Directors
of the Parent, the Merger Subsidiary and the Company pursuant to resolutions
adopted by such Boards, notwithstanding any prior adoption of this Agreement or
approval of the Merger by the respective stockholders of the Merger Subsidiary
or the Company;

(b)  Violation of Order.  By either the Parent or the Merger
Subsidiary, on the one hand, or the Company, on the other, if consummation of
the Merger would violate any preliminary injunction or restraining order or
final, nonappealable order, decree, injunction, restraining order or judgment of
any United States court or other tribunal of competent jurisdiction;

(c)  Other Transactions Involving the Company.  By the Parent if any of
the following shall have occurred:

(i)  Any Person (other than the Parent or any Subsidiary of the Parent) shall
     have commenced (as such term is defined in Rule 14d-2 under the Exchange
     Act), a tender offer or exchange offer to purchase any Company Common Stock
     or securities convertible into such shares such that, upon consummation of
     such offer, such Person would own or control 50% or more of the then
     outstanding Company Common Stock and the Board of Directors of the Company,
     within ten (10) Business Days after such tender or exchange offer shall
     have been so commenced, fails to recommend against acceptance of such
     tender or exchange offer by its stockholders;

(ii) The Company or PL shall have authorized, recommended, proposed or publicly
     announced an intention to authorize, recommend or propose, or entered into,
     an agreement with any Person (other than the Parent or any Subsidiary of
     the Parent) to (A) effect a merger, consolidation or similar transaction
     involving the Company or PL, (B) sell, lease or otherwise dispose of assets
     of the Company or PL representing 10% or more of the consolidated assets of
     the Company and PL, (C) issue, sell or otherwise dispose of (including by
     way of merger, consolidation, share exchange or any similar transaction)
     securities (or options, rights or warrants to purchase), or securities
     convertible into, such securities) representing 10% or more of the voting
     power of the Company, or (D) grant to such Person a license of any
     intellectual property of the Company other than licenses in the ordinary
     course of business relating to the sale of the Company's products;

(iii)Any Person (other than the Parent or any Subsidiary of the Parent)
     shall have acquired beneficial ownership (as such term is defined

                                     A-59
<PAGE>
 
     in Rule 13d-3 under the Exchange Act) or the right to acquire beneficial
     ownership of, or any "group" (as such term is defined under the Exchange
     Act) shall have been formed which beneficially owns or has the right to
     acquire beneficial ownership of, 25% or more of the then outstanding
     Company Common Stock; or

(iv) The Company's Board of Directors shall have withdrawn or modified in a
     manner adverse to the Parent the recommendation of the Company's Board of
     Directors that the stockholders approve this Agreement and the Merger (it
     being understood and agreed that any communication by the Company or its
     Board of Directors to the stockholders of the Company that the Company's
     Board of Directors had determined not to withdraw or modify such
     recommendation, in whole or in part, because such action would or might
     give rise to a right on the part of the Parent to terminate this Agreement
     and/or obligate the Company to pay the Termination Fee shall nevertheless
     be deemed an adverse modification of such recommendation for purposes of
     this Section 6.1(c)(iv)).

(d)  Superior Proposal.  By the Company, in connection with entering
into an agreement for a Superior Proposal as expressly permitted by Section
4.1(f), provided that:  (i) the Company has complied with all provisions
thereof; (ii) immediately following such termination the Company executes a
definitive agreement to consummate the Superior Proposal; (iii) prior to any
such termination:  (x) the Company shall have provided the Parent with four (4)
days' notice of the terms of the Superior Proposal, and (y) the Company shall
have, and shall have caused the Company Representatives to have, negotiated in
good faith, during such four (4) day period, with respect to any proposal made
by the Parent to adjust the terms and conditions of this Agreement as would
enable the Company, consistent with the fiduciary duties of its Board of
Directors, to proceed with the Merger; and (iv) the Company shall have paid the
Parent the Termination Fee.

(e)  By either the Parent or the Company if the Merger shall have not been
consummated on or before November 30, 1998 (the "Termination Date"); provided,
however, that the right to terminate this Agreement under this Section 6.1(e)
shall not be available to any party whose failure to fulfill any obligation
under this Agreement has been the cause of, or resulted in, the failure of the
Effective Time to occur on or before Termination Date.

(f)  By the Company ten (10) days after the Stockholders Meeting (including any
adjournment thereof) if at the Stockholders Meeting (including any adjournment
thereof) this Agreement and the Merger shall fail to be

                                     A-60
<PAGE>
 
approved and adopted by the affirmative vote of the stockholders of the Company
as required under DGCL.

6.2         Termination of Agreement.
            ------------------------ 

          Subject to the provisions of Section 6.1(e), the Merger shall be
          abandoned and this Agreement shall be automatically terminated on the
          Termination Date, or such later date as the Board of Directors of the
          Parent, the Merger Subsidiary and the Company may mutually agree
          pursuant to resolutions adopted by such Boards.

6.3         Effect of Abandonment or Termination.
            ------------------------------------ 

          In the event of termination of this Agreement by either the Parent or
          the Company, as provided in Section 6.1, Section 6.2 or in Article 5
          of this Agreement, this Agreement shall forthwith become void and of
          no further force and effect; provided, however, that:  (a) each of the
          parties shall be entitled to pursue, exercise and enforce any and all
          remedies, rights, powers and privileges available to it at law or in
          equity for any breach of this Agreement ("Remedies") which occurred
          prior to such termination, which, in the case of the Parent, shall be
          in addition to its rights under Section 7.1(b); and (b) Sections
          3.1(d), 3.1(o) and 4.1(a) (insofar as such representations and
          warranties relate to the Company Option Agreement and the transactions
          contemplated thereby), Section 4.1(c), Section 4.2(c), Article 7,
          Section 8.7, Section 8.9, Section 8.10, Section 8.11 and Section 8.12
          shall survive the termination of this Agreement.

7.          EXPENSES.
            -------- 
7.1         Costs and Expenses.
            ------------------ 

(a)  Payment of Own Expenses.  Except as set forth in Section 7.1(b),
whether or not the Merger is consummated, all costs and expenses incurred in
connection with this Agreement and the transactions contemplated hereby shall be
paid by the party incurring such expense, and in connection therewith, each of
the Parent and the Company shall pay, with its own funds, any and all property
or transfer taxes imposed on such party, except that expenses incurred in
connection with printing and mailing the Prospectus/Proxy Statement to the
holders of Company Common Stock shall be shared equally by the Parent and the
Company and that the expenses incurred by either the Parent or the Company
pursuant to the Company Option Agreement shall be borne as provided therein.

(b)  Termination Fee.

(i)  If this Agreement is terminated by the Parent pursuant to Section 6.1(c)(i)
     or (iii) or, at the time of the termination of this

                                     A-61
<PAGE>
 
     Agreement, the Parent had the right to so terminate, and within 12 months
     after such termination the Company executes a definitive agreement to
     implement a Takeover Proposal (whether or not such Takeover Proposal
     triggered the termination right), then the Company shall pay to the Parent
     Termination Fee in an amount equal to $9 million (the "Termination Fee")
     within two (2) Business Days after the execution of such definitive
     agreement.

(ii) If this Agreement is terminated by the Parent pursuant to Section
     6.1(c)(ii), or, at the time of the termination of this Agreement, the
     Parent had the right to so terminate, then within two (2) Business Days
     after any of the conditions set forth in Section 6.1(c)(ii) are satisfied,
     the Company shall pay to the Parent the Termination Fee.

(iii)If this Agreement is terminated by the Parent pursuant to Section
     6.1(c)(iv), or at the time of the termination of this Agreement, the Parent
     had the right to so terminate, then within two (2) Business Days after such
     termination, the Company shall pay to the Parent the Termination Fee;
     provided, however, that the Company shall not be obligated to pay the
     Parent the Termination Fee pursuant to this Section 7.1(b)(iii) in the
     event that (y) the actions of Board of Directors of the Company that gave
     rise to the Parent's right to terminate under Section 6.1(c)(iv) were the
     result of the occurrence of an event which had, or was reasonably expected
     to have, a Material Adverse Effect on the Parent or had caused, or was
     reasonably expected to cause, the Parent to suffer a Material Adverse
     Change and (z) the Board of Directors of the Company made a good faith
     determination, based upon the advice of its legal counsel as to legal
     matters, that such actions were necessary in order to comply with its
     fiduciary duties to the Company stockholders under applicable law. (iv) If
     this Agreement is terminated by the Company pursuant to Section 6.1(d),
     then the Company shall pay to the Parent the Termination Fee prior to such
     termination as provided in Section 6.1(d).

(v)  If following a Takeover Proposal, this Agreement is terminated by either
     the Parent or the Company pursuant to Section 6.1(e), and within 12 months
     after such termination the Company executes with a third party a definitive
     agreement to implement a Takeover Proposal, then the Company shall pay to
     the Parent the Termination Fee within two (2) Business Days after the
     execution of such agreement.

                                     A-62
<PAGE>
 
(vi) If following a Takeover Proposal, this Agreement is terminated by the
     Company pursuant to Section 6.1(f), and within 12 months after such
     termination the Company executes with a third party a definitive agreement
     to implement a Takeover Proposal, then the Company shall pay to the Parent
     the Termination Fee within two (2) Business Days after the execution of
     such agreement.

(vii)For purposes of this Section 7.1(b), whenever the Company shall be
     obligated to pay the Termination Fee, the Company shall pay the Parent by
     wire transfer to an account specified by the Parent.

8.          MISCELLANEOUS.
            ------------- 
8.1         Certification of the Company's Shareholder Votes, Etc.
            ----------------------------------------------------- 

          Prior to the Effective Date, the Company shall deliver to the Parent
          and the Merger Subsidiary a certificate of its Secretary or Assistant
          Secretary setting forth (a) the number of shares of its capital stock
          outstanding and entitled to vote on the adoption of this Agreement,
          (b) the number of votes pertaining to such shares of capital stock,
          and (c) the number of votes cast in favor of and against the approval
          of this Agreement.

8.2         Certification of the Parent's Stockholder Votes, Etc.
            ---------------------------------------------------- 

          Prior to the Effective Date, the Parent shall deliver to the Company
          and the Merger Subsidiary a certificate of its Secretary or Assistant
          Secretary setting forth that the Parent, in its capacity as sole
          stockholder of the Merger Subsidiary, has adopted this Agreement and
          approved the Merger in accordance with the DGCL.

8.3         Termination of Covenants, Representations and Warranties.
            -------------------------------------------------------- 

          The respective covenants, representations and warranties of the
          parties hereto contained in Articles 3 and 4 hereof and in the
          Schedules shall expire and be terminated and extinguished at the
          Effective Time, and none of the parties hereto shall thereafter be
          under any liability whatsoever with respect to such covenants,
          representations and warranties.  This Section 8.3 shall have no effect
          upon any other obligations hereunder of any of the parties hereto,
          whether to be performed before or after the effectiveness of the
          Merger.

8.4         Certain Tax Matters.
            ------------------- 
(a)  The Parent and the Merger Subsidiary hereby jointly and severally
     represent, warrant and covenant to the Company and the Surviving
     Corporation as follows:

                                     A-63
<PAGE>
 
(i)  The fair market value of Parent Common Stock and other consideration
     received by each Company stockholder will be approximately equal to the
     fair market value of Company Common Stock surrendered in the exchange;

(ii) Following the Merger, the Surviving Corporation will hold at least 90
     percent of the fair market value of the Company's net assets and at least
     70 percent of the fair market value of the Company's gross assets and at
     least 90 percent of the fair market value of the Merger Subsidiary's net
     assets and at least 70 percent of the fair market value of the Merger
     Subsidiary's gross assets held immediately prior to the Merger.  For
     purposes of the preceding sentence, amounts paid by the Company or the
     Merger Subsidiary to stockholders who receive cash or other property,
     amounts used by the Company or the Merger Subsidiary to pay reorganization
     expenses and all redemptions and distributions (except for regular, normal
     dividends) made by the Company will be included as assets of the Company or
     the Merger Subsidiary, respectively, immediately prior to the Merger;

(iii)Prior to the Merger, the Parent will be in control of the Merger
     Subsidiary within the meaning of Section 368(c) of the Code;

(iv) The Surviving Corporation has no plan or intention to issue additional
     shares of its stock that would result in the Parent's losing control of the
     Surviving Corporation within the meaning of Section 368(c)(1) of the Code;

(v)  The Parent has no plan or intention to reacquire any of the shares of
     Parent Common Stock to be issued in the Merger, nor does the Parent have
     any knowledge of a plan or intention on the part of a "related party" to
     the Parent (as such term is defined in the regulations under Section 368 of
     the Code) to acquire any of the shares of Parent Common Stock to be issued
     in the Merger;

(vi) The Parent has no plan or intention to liquidate the Surviving Corporation,
     to merge the Surviving Corporation with or into another corporation, to
     sell or otherwise dispose of the stock of the Surviving Corporation, except
     for transfers of stock to corporations controlled by the Parent, or to
     cause the Surviving Corporation to sell or otherwise dispose of any of its
     assets or of any of the assets acquired from the Merger Subsidiary, except
     for dispositions made in the ordinary course of business or transfers of
     assets to a corporation controlled by the Surviving Corporation;

                                     A-64
<PAGE>
 
(vii) The Merger Subsidiary will have no liabilities assumed by the
      Surviving Corporation, and it will not transfer to the Surviving
      Corporation any assets subject to liabilities, in the Merger;

(viii)Following the Merger, the Surviving Corporation will continue the
      historic business of the Company or use a significant portion of its
      historic business assets in a business;

(ix)  The Parent, the Merger Subsidiary, the Company and the shareholders of the
      Company will pay their respective expenses, if any, incurred in connection
      with the Merger;

(x)   There is no intercorporate indebtedness existing between the Parent and 
      the Company or between the Merger Subsidiary and the Company that was
      issued, acquired or will be settled at a discount;

(xi)  The Parent does not own, nor has it owned during the past five (5) years,
      any shares of the stock of the Company;

(xii) No two parties to the Merger are investment companies as defined in
      Sections 368(a)(2)(F)(iii) and (iv) of the Code; and

(xiii)None of the compensation to be received by any shareholder-employees
      of the Company under any employment agreement will be separate
      consideration for, or allocable to, any of their shares of Company Common
      Stock; none of the shares of Parent Common Stock received by any
      shareholder-employees will be separate consideration for, or allocable to,
      any employment agreement; and the compensation paid to any shareholder-
      employees under any employment agreement will be for services actually
      rendered and will be commensurate with amounts paid to third parties
      bargaining at arm's length for similar services.

(b)  The Company and PL hereby jointly and severally represent, warrant and
     covenant to the Parent and the Merger Subsidiary as follows:

(i)  The fair market value of Parent Common Stock and other consideration
     received by each Company stockholder will be approximately equal to the
     fair market value of Company Common Stock surrendered in the exchange;

(ii) Following the Merger, the Surviving Corporation will hold at least 90
     percent of the fair market value of the Company's net assets and at least
     70 percent of the fair market value of the Company's gross assets and at
     least 90 percent of the fair market value of Merger Subsidiary's net assets
     and at least 70 percent of the fair market

                                     A-65
<PAGE>
 
      value of Merger Subsidiary's gross assets held immediately prior to the
      Merger. For purposes of the preceding sentence, amounts paid by the
      Company or the Merger Subsidiary to stockholders who receive cash or other
      property, amounts used by the Company or the Merger Subsidiary to pay
      reorganization expenses and all redemptions and distributions (except for
      regular, normal dividends) made by the Company will be included as assets
      of the Company or the Merger Subsidiary, respectively, immediately prior
      to the Merger;

(iii) Prior to the Merger, neither the Company nor PL will take any action
      which would disqualify the Merger for treatment as a tax-free transaction
      under the Code;

(iv)  Neither the Company nor PL has any knowledge of a plan or intention on the
      part of the holders of Company Common Stock to sell or transfer to the
      Parent or to a "related party" to the Parent (as such term is defined in
      the regulations under Section 368 of the Code) any of the shares of Parent
      Common Stock to be received by such holders in the Merger;

(v)   The Parent, the Merger Subsidiary, the Company and the shareholders of the
      Company will pay their respective expenses, if any, incurred in connection
      with the Merger;

(vi)  There is no intercorporate indebtedness existing between the Parent and 
      the Company or between the Merger Subsidiary and the Company that was
      issued, acquired or will be settled at a discount;

(vii) At the time of the Merger, the Company will not have outstanding any
      warrants, options, convertible securities or any other type of right
      pursuant to which any person could acquire stock in the Company that, if
      exercised or converted, would affect the Parent's acquisition or retention
      of control of the Company, as defined in Section 368(c) of the Code;

(viii)On the date of the Merger, the fair market value of the assets of
      the Company will exceed the sum of its liabilities, plus the amount of
      liabilities, if any, to which the assets are subject; and

(ix)  No two parties to the Merger are investment companies as defined in
      Sections 368(a)(2)(F)(iii) and (iv) of the Code.

(c)  Neither the Parent nor the Surviving Corporation shall have any liability
     to the holders of the Company Common Stock with respect to the tax
     consequences resulting from the transactions contemplated by this

                                     A-66
<PAGE>
 
     Agreement except to the extent that: (A) the representations and warranties
     of the Parent and the Merger Subsidiary set forth in Section 8.4(a) hereof
     are not true and correct on the Effective Date or (B) the covenants of the
     Parent and the Merger Subsidiary set forth in Section 8.4(a) are not
     performed on and after the Effective Date.

8.5         Execution in Counterparts.
            ------------------------- 

          For the convenience of the parties, this Agreement and any amendments,
          supplements, waivers and modifications may be executed in one or more
          counterparts, each of which shall be deemed an original, but all of
          which together shall constitute one and the same document.

8.6         Waivers and Amendments.
            ---------------------- 

          Prior to the Effective Date, this Agreement may be amended, modified
          and supplemented in writing by the parties hereto, and any failure of
          any of the parties hereto to comply with any of its obligations,
          agreements or conditions as set forth herein may be expressly waived
          in writing by the other parties hereto.

8.7         Confidentiality.
            --------------- 

          The Company and the Parent agree that they shall abide by the terms of
          the Confidentiality Agreement between them dated March 27, 1998 (as
          supplemented) (the "Confidentiality Agreement") and the Reciprocal
          Confidentiality Agreement between them dated _________________, 1998
          (the "Reciprocal Confidentiality Agreement"), respectively, and such
          confidentiality agreements shall continue in effect notwithstanding
          the execution of this Agreement.

8.8         Indemnification; Directors and Officers Insurance.
            --------------------------------------------------

          For six (6) years from and after the Effective Time, the Parent agrees
          to cause the Surviving Corporation to, and shall guarantee the
          obligation of the Surviving Corporation to, indemnify and hold
          harmless all past and present officers and directors of the Company to
          the same extent such Persons are indemnified as of the date of this
          Agreement by the Company and PL pursuant to their Company's
          Certificate of Incorporation, Bylaws or agreements in existence on the
          date hereof for acts or omissions occurring at or prior to the
          Effective Time (including, without limitation, acts or omissions
          relating to the negotiation, execution and performance of this
          Agreement and the Company Option Agreement and the transactions
          contemplated hereby and thereby).  The Parent shall provide, or shall
          cause the Surviving Corporation to provide, for an aggregate period of
          not less than six (6) years from the Effective Time, the Company's
          current directors and officers an insurance and indemnification policy
          that provides coverage for events occurring prior to the Effective
          Time (the "D&O Insurance") that is

                                     A-67
<PAGE>
 
          substantially similar (with respect to limits and deductibles) to the
          Company's existing policy or, if substantially equivalent insurance
          coverage is unavailable, the best available coverage; provided,
          however, that the Surviving Corporation shall not be required to pay
          any annual premium for D&O Insurance which is greater than 200% of the
          most recent annual premiums paid by the Company for D&O Insurance.

8.9         Notices.
            ------- 

          All notices, requests, demands and other communications required or
          permitted hereunder shall be in writing and shall be deemed to have
          been duly given upon receipt when delivered by hand against receipt,
          telecopied (upon confirmation of receipt thereof) or mailed, certified
          or registered mail, return receipt requested, postage prepaid:

          To the Company:


          Lloyd H. Malchow, President and CEO
          320 Lakeside Drive
          Suite A
          Foster City, California

               with a copy to:


               Henry Lesser, Esquire
               Heller Ehrman White & McAuliffe
               525 University Avenue
               Palo Alto, California  94301-1800
               Telecopy Number:  (650) 324-0638

          To the Parent or the Merger Subsidiary:


          Roderick P. Jackson, Senior Vice President
          Chestnut Ridge Road
          P.O. Box 4310
          Morgantown, West Virginia  26505
          Telecopy Number:  (304) 599-7284

               with a copy to:


               John R. Previs, Esquire/JoEllen Lyons, Esquire
               Buchanan Ingersoll Professional Corporation
               One Oxford Centre
               301 Grant Street
               Pittsburgh, Pennsylvania  15219
               Telecopy Number:  (412) 562-1041

                                     A-68
<PAGE>
 
          or to such other address as specified in a notice given in like
          manner.

8.10        Entire Agreement; No Third-Party Beneficiaries; Rights of Ownership.
            ------------------------------------------------------------------- 

          This Agreement (including the documents and the instruments referred
          to herein) (a) constitutes the entire agreement and supersedes all
          prior agreements and understandings, both written and oral, among the
          parties with respect to the subject matter hereof and thereof, and (b)
          is not intended to confer upon any Person other than the parties
          hereto or thereto and the indemnitees under Section 8.8 any rights or
          remedies hereunder or thereunder.

8.11        Governing Law.
            ------------- 
          This Agreement shall be governed by and construed in accordance with
          the laws of the State of Delaware without regard to any applicable
          conflicts of laws provisions.

8.12        Partial Invalidity.
            -------------------

          Wherever possible, each provision hereof shall be interpreted in such
          a manner as to be effective and valid under applicable law, but in
          case any one or more of the provisions contained herein shall, for any
          reason, be held to be invalid, illegal or unenforceable in any
          respect, it shall, to the extent possible, be construed in such manner
          as to be legal, valid and enforceable but so as to most nearly retain
          the intent of the parties.  The invalidity, illegality or
          unenforceability of any provision of this Agreement shall not affect
          any other provisions of this Agreement and such provisions shall
          remain in full force and effect.

8.13        Publicity.
            --------- 

          Except as otherwise required by law or the rules of the SEC, the NYSE
          (with respect to the Parent) or the NASD (with respect to the
          Company), for so long as this Agreement is in effect, neither the
          Parent nor the Company shall, nor shall either permit any of its
          respective subsidiaries to, issue or cause the publication of any
          press release or other public announcement with respect to the
          transactions contemplated by this Agreement without the consent of the
          other party as to the nature, contents and dissemination thereof, in
          which case the party proposing such publication shall deliver a copy
          of such release or announcement to the other party along with its
          request for consent, which consent shall not be unreasonably withheld.

8.14        Defined Terms.
            ------------- 
          All capitalized terms used herein without definition shall have the
          meanings given them at the places in this Agreement indicated in
          Appendix A.
          ---------- 

                                     A-69
<PAGE>
 
8.15        Benefit Plans.
            ------------- 
(a)  The eligibility of each employee of the Company (and his or her spouse and
     dependents) to participate in the welfare benefit plans of the Parent or
     the Surviving Corporation after the Effective Time and the coverage of each
     such participant in each such plan shall be determined without regard to
     any preexisting condition, waiting period, actively-at-work or similar
     exclusion or condition, except for any such condition or exclusion to which
     the employee is subject under the applicable welfare plan of the Company as
     of the Effective Time.  Participants in such plans of the Company shall
     receive credit, under the welfare benefit plans of the Parent or the
     Surviving Corporation in which they participate after the Effective Time,
     toward annual co-insurance and deductible limitations and requirements for
     any payments made for eligible charges incurred by them during the calendar
     year in which the Effective Time occurs under the applicable welfare plans
     of the Company.  In addition, employees of the Surviving Corporation shall
     receive credit, for purposes of determining vesting and eligibility under
     its retirement, welfare, vacation and similar plans or policies, for
     service with the Company prior to the Effective Time.

(b)  The Persons employed by the Company immediately prior to the Effective Time
     shall be eligible to participate in the employment severance programs
     provided by the Parent or the Surviving Corporation from time to time, and
     such persons shall receive credit under such programs for services with the
     Company prior to the Effective Date.

8.16        Enforcement of Agreement.
            ------------------------ 

          The parties hereto agree that irreparable damage would occur in the
          event that any of the provisions of this Agreement was not performed
          in accordance with its specific terms or was otherwise breached. It is
          accordingly agreed that the parties shall be entitled to an injunction
          to prevent breaches of this Agreement and to enforce specifically the
          terms and provisions hereof in any Delaware Chancery Court, this being
          in addition to any other remedy to which they are entitled at law or
          equity.  Notwithstanding the foregoing, if jurisdiction does not
          properly lie in the Delaware Chancery Court, the parties shall submit
          to the jurisdiction of the United States Federal District Court for
          the District of Delaware. The parties agree that such courts shall
          have exclusive jurisdiction to consider any claims hereunder or
          relating hereto.

8.17        Waiver of Jury Trial.
            -------------------- 

          Each party acknowledges and agrees that any controversy which may
          arise under this Agreement is likely to involve complicated and
          difficult issues, and therefore each such party hereby irrevocably and
          unconditionally waives any right such

                                     A-70
<PAGE>
 
          party may have to a trial by jury in respect of any litigation
          directly or indirectly arising out of or relating to this Agreement,
          or the transactions contemplated by this Agreement. Each party
          certifies and acknowledges that (i) no representative, agent or
          attorney of any other party has represented, expressly or otherwise,
          that such other party would not, in the event of litigation, seek to
          enforce the foregoing waiver, (ii) each party understands and has
          considered the implications of this waiver, (iii) each party makes
          this waiver voluntarily, and (iv) each party has been induced to enter
          into this Agreement by, among other things, the mutual waivers and
          certifications in this Section 8.17.

8.18        No Presumption Against the Draftsman.
           ------------------------------------ 

          Each party having been represented in the negotiation of this
          Agreement, and having had ample opportunity to review the language
          hereof, there shall be no presumption against any party on the ground
          that such party was responsible for preparing this Agreement or any
          part thereof.

                                     A-71
<PAGE>
 
     IN WITNESS WHEREOF, this Agreement has been executed by each of the
Constituent Corporations and the Parent, all on the date first above written.

                                    PENEDERM INCORPORATED

 


Attest:                                        By:
       ----------------------------               ----------------------------
        Name:  Michael A. Bates                   Name:  Lloyd H. Malchow
        Title:  Vice President, Finance and       Title:  President and CEO
                Administration, Chief Financial
                Officer

                                    MLI ACQUISITION CORP.



Attest:                                        By:
       ----------------------------               ----------------------------
        Name:  Donald C. Schilling                Name:  Roderick P. Jackson
        Title:  Vice President Finance            Title:  President

                                    MYLAN LABORATORIES INC.



Attest:                                        By:
       ----------------------------               ----------------------------
        Name:  Donald C. Schilling                Name:  Roderick P. Jackson
        Title:  Vice President Finance            Title:  Senior Vice President



                                     A-72
<PAGE>
 
                                   APPENDIX A

                                  GLOSSARY OF

                        DEFINED TERMS/SECTION REFERENCES

                                       IN

                          AGREEMENT AND PLAN OF MERGER

                                  BY AND AMONG

                             PENEDERM INCORPORATED

                                      AND

                             MLI ACQUISITION CORP.

                                      AND

                            MYLAN LABORATORIES INC.

<TABLE>
<CAPTION>
DEFINED TERM                                                            SECTION REFERENCE
- ------------                                                            -----------------
<S>                                                                     <C>
Agreement                                                               Preamble
- ---------                                                               --------
Amended and Restated Certificate of Incorporation                       Section 1.2
Business Day                                                            Section 2.4
Certificates                                                            Section 2.1(b)(ii)
Closing                                                                 Section 2.4
Code                                                                    Recital 5
Common Stock Investment Agreement                                       Section 3.1(b)(i)
Company                                                                 Preamble
Company Affiliates                                                      Section 3.1(s)
Company Common Stock                                                    Recital 7
Company Contracts                                                       Section 3.1(m)
Company Employee Stock Purchase Plan                                    Section 2.3(d)
Company Financial Statements                                            Section 3.1(e)
Company 401(k) Plan                                                     Section 3.1(b)(i)
</TABLE>

                                     A-73
<PAGE>
 
<TABLE>
<CAPTION>
DEFINED TERM                                                            SECTION REFERENCE
- ------------                                                            -----------------
<S>                                                                     <C>
Company Option Agreement                                                Recital 7
Company Permits                                                         Section 3.1(h)
Company Preferred Stock                                                 Section 3.1(b)(i)
Company Representatives                                                 Section 4.1(f)(i)
Company Rights Plan                                                     Section 3.1(c)
Company SEC Documents                                                   Section 3.1(e)
Company Stock Option Plans                                              Section 2.3(a)
Company Stock Options                                                   Section 3.1(b)(i)
Company Warrant                                                         Section 2.3(b)
Company Warrant Shares                                                  Section 2.3(b)
Confidentiality Agreement                                               Section 8.7
Constituent Corporations                                                Preamble
Contract Manufacturer                                                   Section 3.1(k)(iii)
D&O Insurance                                                           Section 8.8
DGCL                                                                    Recital 2
Dillon Read                                                             Section 3.2(n)
Drug Regulatory Agency                                                  Section 3.1(k)(i)
Effective Date                                                          Section 1.4
Effective Time                                                          Section 1.4
Employee Benefit Plan                                                   Section 3.1(cc)(i)
Environmental Laws                                                      Section 3.1(ii)(ii)
ERISA                                                                   Section 3.1(cc)(i)
Exchange Act                                                            Section 3.1(d)
Exchange Agent                                                          Section 2.1(b)(i)
Exchange Fund                                                           Section 2.1(b)(i)
Exchange Ratio                                                          Section 2.1(a)
FDA                                                                     Section 3.1(k)(ii)
FDA Act                                                                 Section 3.1(k)(i)
Governmental Entity                                                     Section 3.1(d)

</TABLE>

                                     A-74
<PAGE>
 
<TABLE>
<CAPTION>
DEFINED TERM                                                            SECTION REFERENCE
- ------------                                                            -----------------
<S>                                                                     <C>
HSR Act                                                                 Section 3.1(d)
Investor                                                                Section 3.1(b)(i)
IRS                                                                     Section 3.1(i)
knowledge of the Company                                                Section 3.1(j)
knowledge of the Parent                                                 Section 3.2(i)
material                                                                Section 3.1(ee)
Material Adverse Change                                                 Section 3.1(a)(i)
Material Adverse Effect                                                 Section 3.1(a)(i)
Merger                                                                  Recital 2
Merger Subsidiary                                                       Preamble
NASD                                                                    Section 3.1(d)
NASDAQ                                                                  Section 3.1(d)
NYSE                                                                    Section 2.1(d)
Parent                                                                  Preamble
Parent Affiliates                                                       Section 3.2(p)
Parent Common Stock                                                     Section 2.1(a)
Parent Financial Statements                                             Section 3.2(e)
Parent Permits                                                          Section 3.2(h)
Parent Preferred Stock                                                  Section 3.2(b)(i)
Parent SEC Documents                                                    Section 3.2(e)
Parent Stock Option Plans                                               Section 3.2(b)(i)
Parent Stock Options                                                    Section 3.2(b)(i)
PCBs                                                                    Section 3.1(ii)(i)
Person                                                                  Section 4.1(f)(v)
PL                                                                      Section 3.1(a)(ii)
Prospectus/Proxy Statement                                              Section 3.1(c)
Reciprocal Confidentiality Agreement                                    Section 8.7
Registration Statement                                                  Section 3.2(c)
Regulated Substance                                                     Section 3.1(ii)(ii)
</TABLE>

                                     A-75
<PAGE>
 
<TABLE>
<CAPTION>
DEFINED TERM                                                            SECTION REFERENCE
- ------------                                                            -----------------
<S>                                                                     <C>
Remedies                                                                Section 6.3
Scheduled Closing Date                                                  Section 2.4
SEC                                                                     Section 2.3(c)
Section 414 Affiliate                                                   Section 3.1(cc)(iv)
Securities Act                                                          Section 3.1(d)
Stockholders Meeting                                                    Section 4.1(m)
Subsidiary                                                              Section 3.2(a)
Subsidiary Common Stock                                                 Section 2.2
Superior Proposal                                                       Section 4.1(f)(iv)
Surviving Corporation                                                   Recital 2
Takeover Proposal                                                       Section 4.1(f)(iii)
Tax Return                                                              Section 3.1(i)
Taxes                                                                   Section 3.1(i)
Termination Date                                                        Section 6.1(e)
Termination Fee                                                         Section 7.1(b)(i)
Transaction Agreements                                                  Section 3.1(l)
Unexercised Options                                                     Section 2.3(a)
Voting Agreements                                                       Recital 8
Warrant Holder                                                          Section 2.3(b)
</TABLE>

                                     A-76
<PAGE>
 
                                   APPENDIX B



                  AMENDED AND RESTATED STOCK OPTION AGREEMENT

















<PAGE>

 
                  AMENDED AND RESTATED STOCK OPTION AGREEMENT

    AMENDED AND RESTATED STOCK OPTION AGREEMENT, dated as of June 24, 1998 (the
"Agreement"), by and between Mylan Laboratories Inc., a Pennsylvania corporation
("Parent"), and Penederm Incorporated, a Delaware corporation (the "Company").

                                    RECITALS
                                    --------

     A.  Concurrently with the execution and delivery of this Agreement, the
Company, Parent and MLI Acquisition Corp., a Delaware corporation and wholly
owned subsidiary of Parent ("Subsidiary") are entering into an Agreement and
Plan of Merger, dated as of the date hereof (the "Merger Agreement"), providing
for, among other things, the merger of Subsidiary  with and into the Company
(the "Merger"), with the Company as the surviving corporation in the Merger.

     B.  As a condition and inducement to Parent's and Subsidiary's willingness
to enter into the Merger Agreement, Parent has requested that the Company agree,
and the Company has agreed, to grant Parent an option to purchase shares of the
Company's common stock on the terms and subject to the conditions set forth
herein.

     C.  Capitalized terms not otherwise defined herein shall have the meanings
ascribed to them in the Merger Agreement.

     D.  This Amended and Restated Stock Option Agreement amends and restates in
its entirety the Stock Option Agreement dated June 24, 1998 by and between 
Parent and the Company.

     NOW, THEREFORE, in consideration of the foregoing and the respective
representations, warranties, covenants and agreements set forth herein and in
the Merger Agreement and for other good and valuable consideration, the receipt
and adequacy of which are hereby acknowledged, the parties hereto, intending to
be legally bound, agree as follows:

1.  Grant of Option.  Subject to the terms and conditions set forth herein, the
    ---------------                                                            
Company hereby grants to Parent an unconditional, irrevocable option (the
"Option") to purchase up to 1,717,878 (as adjusted as set forth herein) fully
paid and nonassessable shares (individually an "Option Share" and collectively
the "Option Shares") of Common Stock, par value $.01 per share of Company
("Company Common Stock"), at a purchase price of $20 (as adjusted as set forth
herein) per Option Share (the "Purchase Price") payable in cash; provided,
                                                                 -------- 
however, that in no event shall the number of Option Shares for which the Option
- -------                                                                         
is exercisable together with the number of shares owned by Parent, if any,
exceed 19.9% of the Company's issued and outstanding shares of Company Common
Stock without giving effect to any shares subject or issued pursuant to the
Option.  The number of Option Shares that may be received upon exercise of the
Option and the Purchase Price are each subject to adjustment as set forth in
Section 9 hereof and as otherwise provided herein.


                                      B-1
<PAGE>
 
2.  Exercise of Option.  (a) Subject to any applicable requirements of law,
    ------------------                                                     
Parent may exercise the Option, in whole or in part, at any time or from time to
time after the occurrence of any one of the following events (a "Purchase
Event"):  (A) any of the following occurs prior to the earlier of the Effective
Time or the termination of the Merger Agreement in accordance with its terms:
(i) any Person (other than Parent or any of its subsidiaries) shall have
commenced (as such term is defined in Rule 14d-2 under the Securities Exchange
Act of 1934 (the "Exchange Act")) a tender offer, or shall have filed a
registration statement under the Securities Act of 1933 (the "Securities Act")
with respect to an exchange offer, to purchase any shares of Company Common
Stock such that, upon consummation of such offer, such person or a "group" (as
such term is defined under the Exchange Act) of which such person is a member
shall have acquired beneficial ownership (as such term is defined in Rule 13d-3
of the Exchange Act), or the right to acquire beneficial ownership, of 25% or
more of the then outstanding Company Common Stock; (ii) the Company or any of
its subsidiaries shall have authorized, recommended, proposed or publicly
announced an intention to authorize, recommend or propose, or entered into, an
agreement, including without limitation, an agreement in principle, with any
person (other than Parent or any of its subsidiaries) to effect or provide for
the consummation of a Takeover Proposal; (iii) any Person (other than Parent or
any of its subsidiaries) shall solicit proxies or consents or announce a bona
fide intention to solicit proxies or consents from the Company's stockholders
(y) in opposition to the Merger, the Merger Agreement or any related
transactions or (z) relating to a Takeover Proposal (other than solicitations of
stockholders seeking approval of the Merger, the Merger Agreement or any related
transactions), and the stockholders of the Company shall have failed to approve
the Merger; or (iv) any Person (other than Parent or any of its subsidiaries)
shall have acquired beneficial ownership (as such term is defined in Rule 13d-3
under the Exchange Act) or the right to acquire beneficial ownership of, or any
"group" (as such term is defined under the Exchange Act) shall have been formed
which beneficially owns or has the right to acquire beneficial ownership of,
shares of Company Common Stock (other than trust account shares) aggregating 25%
or more of the then outstanding Company Common Stock; or (B) the termination of
the Merger Agreement under circumstances entitling Parent to payment of the
Termination Fee within 2 Business Days of such termination under any of the
provisions of Section 7.1(b) of the Merger Agreement; or (C) within twelve (12)
months after the Merger Agreement is terminated pursuant to Section 6.1(e) or
(f) thereof, the Company executes a definitive agreement to implement a Takeover
Proposal with a third party who had submitted a Takeover Proposal prior to the
Termination Date (a "Proponent"); or (D) within six (6) months after the Merger
Agreement is terminated pursuant to Section 6.1(e) or (f) thereof, the Company
executes a definitive agreement to implement a Takeover Proposal with a third
party other than a Proponent provided that the Company received a Takeover
Proposal prior to the Termination Date.


                                      B-2
<PAGE>
 
(b)  Except as provided in the last sentence of this Section 2(b) the Option
     shall terminate and be of no further force and effect upon the earliest to
     occur (the "Expiration Date") of (A) the Effective Time, (B) 12 months
     after the first occurrence of a Purchase Event, of the type described in
     subclauses (A)(i) through (iv) of Section 2(a) hereof or subclause (B) of
     Section 2(a) hereof and (C) six months after the first occurrence of a
     Purchase Event of the type described in subclauses (C) or (D) of Section
     2(a) hereof. Notwithstanding the termination of the Option, Parent shall be
     entitled to purchase the Option Shares if it has exercised the Option in
     accordance with the terms hereof prior to the termination of the Option and
     the termination of the Option shall not affect any rights hereunder which
     by their terms do not terminate or expire prior to or as of such
     termination.

(c)  In the event that Parent wishes to exercise the Option, it shall send to
     the Company a written notice (the date of which being herein referred to as
     the "Notice Date") specifying (i) the total number of Option Shares it
     wishes to purchase pursuant to such exercise and (ii) a date not earlier
     than three business days nor later than 20 business days from the Notice
     Date for the closing of such purchase (the "Option Closing Date");
     provided, however, that (i) if the closing of the purchase and sale
     --------  --------                                                 
     pursuant to the Option (the "Option Closing") cannot be consummated by
     reason of any applicable judgment, decree, order, law or regulation, the
     period of time that otherwise would run pursuant to this sentence shall run
     instead from the date on which such restriction on consummation has expired
     or been terminated and (ii) without limiting the foregoing, if prior
     notification to or approval of any regulatory authority is required in
     connection with such purchase, Parent and the Company shall promptly file
     the required notice or application for approval and shall cooperate in the
     expeditious filing of such notice or application, and the period of time
     that otherwise would run pursuant to this sentence shall run instead from
     the date on which, as the case may be, (A) any required notification period
     has expired or been terminated or (B) any required approval has been
     obtained, and in either event, any requisite waiting period has expired or
     been terminated.  Except as otherwise agreed in writing by the parties, the
     place of the Option Closing shall be at the offices of Buchanan Ingersoll
     Professional Corporation, One Oxford Centre, 301 Grant Street, 20th Floor,
     Pittsburgh, PA  15219-1410, and the time of the Option Closing shall be
     10:00 a.m. (Eastern Time) on the Option Closing Date.

3.  Payment and Delivery of Certificates.  (a) At the Option Closing, Parent
    ------------------------------------                                    
shall deliver to the Company the Purchase Price for the Option Shares so
designated and being purchased in immediately available funds by wire transfer
to a bank account designated in writing by the Company or by certified check or
bank check in an amount equal to the Purchase Price multiplied by the number of
Option Shares being purchased.  At any Option Closing, Parent shall also deliver
a letter, in form and substance reasonable acceptable to the Company, agreeing
that Parent will not offer to sell or otherwise dispose of such Option Shares in
violation of applicable law or the provisions of this Agreement.
 
(b)  At any Option Closing, simultaneously with the delivery of the Purchase
     Price as provided in Section 3(a), the Company shall deliver to Parent (i)
     a certificate or certificates representing the Option Shares to be
     purchased at the Option Closing, which Option Shares shall be free and
     clear of all liens, claims, charges and encumbrances of any kind whatsoever
     and (ii) if the Option should be exercised in part only, a new Option
     evidencing the rights of the Parent to purchase the balance of the Option
     Shares purchasable hereunder in the form of a Stock Option Agreement
     identical to this Agreement save only the number of Option Shares subject
     thereto.  If at the time of issuance of the Option Shares pursuant to the
     exercise of the Option hereunder, the Company shall not have redeemed any
     rights issued under the Company Shareholders Rights Plan dated November 20,
     1996 (the "Company Rights Plan"), or shall have issued any similar rights,
     then each Option Share issued pursuant to such exercise shall also
     represent a corresponding right or security or new rights with terms
     substantially the

                                      B-3
<PAGE>
 
     same as and at least as favorable to Parent as are provided under the
     Company Rights Plan or any similar agreement then in effect.

(c)  Certificates for the Option Shares delivered at the Option Closing shall
     have typed or printed thereon a restrictive legend which shall read
     substantially as follows:

          "THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
          REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY BE
          REOFFERED OR SOLD ONLY IF SO REGISTERED OR IF AN EXEMPTION FROM SUCH
          REGISTRATION IS AVAILABLE.  SUCH SECURITIES ARE ALSO SUBJECT TO
          ADDITIONAL RESTRICTIONS ON TRANSFER AS SET FORTH IN THE STOCK OPTION
          AGREEMENT, DATED JUNE 24, 1998, A COPY OF WHICH MAY BE OBTAINED FROM
          THE SECRETARY OF PENEDERM INCORPORATED CORPORATION AT ITS PRINCIPAL
          EXECUTIVE OFFICES."

(d)  It is understood and agreed that:  (i) the reference to the resale
     restrictions of the Securities Act of 1933, as amended (the  "Securities
     Act"), in the above legend shall be removed by delivery of substitute
     certificate(s) without such reference if the Parent shall have delivered to
     the Company a copy of a letter from the staff of the Securities and
     Exchange Commission (the "SEC"), or an opinion of counsel, in form and
     substance satisfactory to the Company, to the effect that such legend is
     not required for purposes of the Securities Act; (ii) the reference to the
     provisions of this Agreement in the above legend shall be removed by
     delivery of substitute certificate(s) without such reference if the shares
     have been sold or transferred in compliance with the provisions of this
     Agreement and under circumstances that do not require the retention of such
     reference; and (iii) the legend shall be removed in its entirety as to
     those Option Shares with respect to which the conditions in the preceding
     clauses (i) and (ii) are both satisfied.  In addition, such certificates
     shall bear any other legend as may be required by law.

4.  Representations and Warranties of the Company.  The Company hereby
    ---------------------------------------------                     
represents and warrants to Parent as follows:

(a)  Due Authorization.  The Company has all requisite corporate power and
     -----------------                                                    
     authority to enter into this Agreement and to consummate the transactions
     contemplated hereby.  The execution and delivery of this Agreement by the
     Company and the consummation by the Company of the transactions
     contemplated hereby have been duly authorized by all necessary corporate
     action on the part of the Company.  This Agreement has been duly executed
     and delivered by the Company and constitutes a legal, valid and binding
     obligation of the Company, enforceable against the Company in accordance
     with its terms.

(b)  Authorized Stock.  The Company's representations and warranties in Section
     ----------------                                                          
     3.1(a) of the Merger Agreement are incorporated herein by reference.
     Without limiting the generality or effect of the foregoing, the Company has
     taken all necessary corporate and other action to authorize and reserve
     and, to permit it to issue, and, at all times from the date hereof


                                      B-4
<PAGE>
 
     until the obligation to deliver Option Shares upon the exercise of the
     Option terminates, shall have reserved for issuance, upon exercise of the
     Option, shares of Company Common Stock necessary for Parent to exercise the
     Option, and the Company shall take all necessary corporate action to
     authorize and reserve for issuance all additional shares of Company Common
     Stock or other securities which may be issued pursuant to Section 9 upon
     exercise of the Option. The shares of Company Common Stock to be issued
     upon due exercise of the Option, including all additional shares of Company
     Common Stock or other securities which may be issuable upon exercise of the
     Option or any Substitute Option pursuant to Section 9, upon issuance
     pursuant hereto, shall be duly and validly issued, fully paid and
     nonassessable, and shall be delivered free and clear of all liens, claims,
     charges and encumbrances of any kind or nature whatsoever, including
     without limitation any preemptive rights of any stockholder of the Company.

(c)  No Conflicts.  The execution and delivery of this Agreement does not, and
     ------------                                                             
     the consummation of the transactions contemplated by this Agreement and
     compliance with the provisions of this Agreement shall not, conflict with,
     or result in any violation of, or default (with or without notice or lapse
     of time or both) under, or give rise to a right of termination,
     cancellation or acceleration of any obligation or loss of a material
     benefit under, or result in the creation of any Lien upon any of the
     properties or assets of the Company or any of its subsidiaries under, (i)
     the certificate of incorporation or by-laws of the Company or the
     comparable organizational documents of any subsidiary of the Company, (ii)
     any loan or credit agreement, note, bond, mortgage, indenture, lease or
     other agreement, instrument, permit, concession, franchise or license
     applicable to the Company or any subsidiary of the Company or their
     respective properties or assets, or (iii) any judgment, order, decree,
     statute, law, ordinance, rule or regulation applicable to the Company or
     any subsidiary of the Company or their respective properties or assets,
     other than, in the case of clauses (ii) and (iii), any such conflicts,
     violations, defaults, rights, losses or Liens that individually or in the
     aggregate would not (x) have a Material Adverse Effect on the Company, (y)
     impair the ability of the Company to perform its obligations under this
     Agreement or the Merger Agreement, or (z) prevent or materially delay the
     consummation of any of the transactions contemplated by this Agreement.

(d)  State Takeover Statutes.  Neither Section 203 of the Delaware General
     -----------------------                                              
     Corporation Act, nor any similar provision contained in the charter or by-
     laws of the Company, is applicable to the acquisition of Option Shares
     pursuant to this Agreement.

5.  Representations and Warranties of Parent.  Parent hereby represents and
    ----------------------------------------                               
warrants to the Company that:

(a)  Due Authorization.  Parent has all requisite corporate power and authority
     -----------------                                                         
     to enter into this Agreement and to consummate the transactions
     contemplated hereby.  The execution and delivery of this Agreement by
     Parent and the consummation by Parent of the transactions contemplated
     hereby have been duly authorized by all necessary corporate action on the
     part of Parent.  This Agreement has been duly executed and delivered by
     Parent and constitutes a legal, valid and binding obligation of Parent,
     enforceable against Parent in accordance with its terms.


                                      B-5
<PAGE>
 
(b)  No Conflicts.  The execution and delivery of this Agreement does not, and
     ------------                                                             
     the consummation of the transactions contemplated by this Agreement and
     compliance with the provisions of this Agreement hereby shall not, conflict
     with or result in any violation of, or default (with or without notice or
     lapse of time or both) under, or give rise to a right of termination,
     cancellation or acceleration of any obligation or loss of a material
     benefit under, or result in the creation of any Lien upon any of the
     properties or assets of Parent under, (i) the certificate of incorporation
     or by-laws of Parent or the comparable organizational documents of Parent,
     (ii) any loan or credit agreement, note, bond, mortgage, indenture, lease
     or other agreement, instrument, permit, concession, franchise or license
     applicable to Parent or its properties or assets, or (iii) any judgment,
     order, decree, statute, law, ordinance, rule or regulation applicable to
     Parent or its properties or assets, other than, in the case of clauses (ii)
     and (iii), any such conflicts, violations, defaults, rights, losses or
     Liens that individually or in the aggregate would not (x) have a material
     adverse effect on Parent, (y) impair the ability of Parent to perform its
     obligations under this Agreement or the Merger Agreement, or (z) prevent or
     materially delay the consummation of any of the transactions contemplated
     by this Agreement.

(c)  Purchase Not for Distribution.  Any Option Shares or other securities
     -----------------------------                                        
     acquired by Parent upon exercise of the Option shall not be transferred or
     otherwise disposed of except in a transaction registered, or exempt from
     registration, under the Securities Act.

6.  Repurchase of Option at Request of Parent.  (a)  At the request of Parent
    -----------------------------------------                                
and in Parent's sole discretion, at any time during the period beginning upon
the first occurrence of a Repurchase Event (as defined in Section 6(c)) and
ending 6 months thereafter, the Company shall repurchase from Parent the Option
(unless the Option shall have expired or been terminated) and all shares of
Common Stock purchased by Parent upon exercise of the Option that are
beneficially owned by Parent on the date upon which Parent requests that the
Company repurchase the Option or Option Shares under this Section 6(a) (the
"Request Date").  Such repurchase shall be at an aggregate price (the "Put
Price") equal to the sum of:

          (x) the aggregate Purchase Price paid by Parent for all Option Shares
     previously purchased upon exercise of the Option that are beneficially
     owned by Parent on the Request Date;

          (y) the excess, if any, of the average of the last sales price for
     Company Common Stock for the ten trading days ending on the day immediately
     preceding the Put Closing Date (the "Market Price") over the Option Price
     paid by Parent for each share of Company Common Stock with respect to which
     the Option has been exercised that are beneficially owned by Parent on the
     Request Date, multiplied by the number of such shares; and

          (z) the excess, if any, of the Market Price of Company Common Stock at
     the Put Closing Date over the Option Price (determined as if the Put
     Closing Date were the Option Closing Date) multiplied by the number of
     Option Shares with respect to which the Option has not been exercised;
     provided that, in the case of Option Shares with respect to which the
     Option has been exercised but the Option Closing Date has not

                                      B-6
<PAGE>
 
     occurred, the Option Closing Date shall be suspended and the Option shall
     be treated, for purposes of this clause (z), as if it had not been
     exercised.

 
(b)  If Parent exercises its rights under this Section 6, the Company shall,
     within 10 business days after the Request Date (the "Put Closing Date"),
     pay the Put Price to Parent in immediately available funds, by wire
     transfer to a bank account designated by Parent, Parent shall, against
     receipt of the payment therefore, surrender to the Company the Option and
     the certificates evidencing Option Shares previously purchased upon
     exercise of the Option that are beneficially owned by Parent on the Request
     Date; and Parent shall be deemed to have represented and warranted that it
     has sole ownership of such Option Shares, free and clear of all liens,
     claims, charges, and encumbrances of any kind.  Notwithstanding the
     foregoing, if the Company is prohibited from paying all or any portion of
     the Put Price by reason of any applicable judgment, decree, order, law, or
     regulation, the Company shall immediately pay that portion of the Put Price
     that it is not prohibited from paying, shall from time to time thereafter
     immediately pay such further portion of the Put Price that it is not then
     prohibited from paying, and, in all cases, shall pay the balance of the Put
     Price within 10 business days after such prohibition has expired or been
     terminated.  Upon receipt of a partial payment of the Put Price, Parent
     shall surrender a portion of the Option and/or Option Shares, as selected
     by Parent, corresponding (as closely as practicable) to the portion of the
     Put Price received by Parent.

(c)  As used herein, a "Repurchase Event" means any of the following:  (i) a
     termination of the Merger Agreement by the Board of Directors of the
     Company under Section 6.1(d) of the Merger Agreement; (ii) an occurrence of
     both (A) a Purchase Event of the type described in subclauses (A),or (C) of
     Section 2(a) hereof other than a termination of the Merger Agreement
     referred to in clause (i) of this sentence and (B) consummation of a
     Takeover Proposal within twelve (12) months after termination of the Merger
     Agreement; (or) (iii) an occurrence of both (A) a Purchase Event of the
     type described in subclause (D) of Section 2(a) hereof and (B) consummation
     of a Takeover Proposal within six (6) months after the termination of the
     Merger Agreement.  A Repurchase Event referred to in clause (ii) or (iii)
     of the preceding sentence will occur when the last of the events referred
     to in clauses (ii)(A) and (ii) (B) occurs.

7.  Registration Rights.  Parent may, by written notice (the "Registration
    -------------------                                                   
Notice") request the Company to register under the Securities Act all or any
part of the capital stock of the Company acquired under this Agreement and
beneficially owned by Parent (the "Registrable Securities").  The Company
(and/or any Person designated by the Company) shall thereupon have the option
exercisable by written notice delivered to Parent within 10 business days after
the receipt of the Registration Notice, irrevocably to agree to purchase all or
any part of the Registrable Securities for cash at a price equal to the product
of (i) the number of Registrable Securities and (ii) the fair market value of
such shares.  Any such purchase of Registrable Securities by the Company
hereunder shall take place at a closing to be held at the principal executive
offices of the Company or its counsel at any reasonable date and time designated
by the Company and/or such designee in such notice within 20 business days after
delivery of such notice.  Any payment of the shares to be purchased shall be
made by delivery at the time of such closing of the purchase price for the
Registrable Securities in immediately available funds.  For purposes of his
Agreement the term Registrable Securities shall not include shares of capital

                                      B-7
<PAGE>
 
stock acquired under this Agreement that may be sold pursuant to Rule 144(k) of
the Securities Act.

          If the Company does not elect to exercise its option pursuant to this
Section 7 with respect to all Registrable Securities, it shall use its best
efforts to effect, as promptly as practicable, the registration under the
Securities Act of the unpurchased Registrable Securities; provided, however,
                                                          --------  --------
that (i) Parent shall be entitled to no more than an aggregate of two effective
registration statements hereunder and (ii) the Company will not be required to
file any such registration statement during any period of time (not to exceed 40
days after such request in the case of clause (A) below or 90 days in the case
of clauses (B) and (C) below) when (A) the Company is in possession of material
non-public information which it reasonably believes would be detrimental to be
disclosed at such time and, in the written opinion of counsel to such Company,
such information would have to be disclosed if a registration statement were
filed at that time; (B) such Company is required under the Securities Act to
include audited financial statements for any period in such registration
statement and such financial statements are not yet available for inclusion in
such registration statement; or (C) such Company determines, in its reasonable
judgment, that such registration would interfere with any financing, acquisition
or other material transaction involving the Company or any of its affiliates.
If consummation of the sale of any Registrable Securities pursuant to a
registration hereunder does not occur within 90 days after the filing with the
Securities and Exchange Commission of the registration statement becomes
effective, the provisions of this Section 7 shall again be applicable to any
proposed registration, provided, however, that neither party shall be entitled
                       -------- ---------                                     
to request more than two registrations pursuant to this Section 7.  The Company
shall use its reasonable best efforts to cause any Registrable Securities
registered pursuant to this Section 7 to be qualified for sale under the
securities or Blue Sky laws of such jurisdictions as Parent may reasonably
request and shall continue such registration or qualification in effect in such
jurisdiction; provided, however, that the Company shall not be required to
              --------  --------                                          
qualify to do business in, or consent to general service of process in, any
jurisdiction by reason of this provision.

          The registration rights set forth in this Section 7 are subject to the
condition that Parent shall provide the Company with such information with
respect to such holder's Registrable Securities, the plans for the distribution
thereof, and such other information with respect to such holder, as, in the
reasonable judgment of counsel for the Company, is necessary to enable the
Company to include in such registration statement all material facts required to
be disclosed with respect to a registration thereunder.

          A registration effected under this Section 7 shall be effected at the
Company's expense, except for underwriting discounts and commissions and the
fees and expenses of counsel to Parent, and the Company shall provide to any
underwriter such documentation (including certificates, opinions of counsel and
"comfort" letters from auditors) as are customary in connection with
underwritten public offerings as such underwriters may reasonably require.  In
connection with any such registration, the parties agree (i) to indemnify each
other and any underwriters in the customary manner and (ii) to enter into an
underwriting agreement in form and substance customary to transactions of this
type with any underwriters participating in such offering.

                                      B-8
<PAGE>
 
8.  Listing.  If shares of Company Common Stock or any other securities to be
    -------                                                                  
acquired upon exercise of the Option are then listed on the Nasdaq National
Market (or any other national securities exchange or national securities
quotation system), the Company, upon the request of Parent, shall promptly file
an application to list the shares of Company Common Stock or other securities to
be acquired upon exercise of the Option on the Nasdaq National Market (or such
other national securities exchange or national securities quotation system) and
shall use reasonable efforts to obtain approval of such listing as promptly as
practicable.

9.  Adjustment Upon Changes in Capitalization, Etc.  (a) In the event of any
    ----------------------------------------------                          
change in Company Common Stock by reason of a stock dividend, split-up, merger,
recapitalization, combination, exchange of shares or similar transaction, the
type and number of shares or securities subject to the Option, and the Purchase
Price therefor, shall be adjusted appropriately, and proper provision shall be
made in the agreements governing such transaction, so that Parent shall receive
upon exercise of the Option the number and class of shares or other securities
or property that Parent would have received in respect of Company Common Stock
if the Option had been exercised immediately prior to such event or the record
date therefor, as applicable.  Subject to Section 1, and without limiting the
parties' relative rights and obligations under the Merger Agreement, if any
additional shares of Company Common Stock are issued after the date of this
Agreement (other than pursuant to an event described in the first sentence of
this Section 9(a)), the number of shares of Company Common Stock subject to the
Option shall be adjusted so that, after such issuance, it equals 19.9% of the
number of shares of Company Common Stock then issued and outstanding, without
giving effect to any shares subject to or issued pursuant to the Option.
 
(b)  Without limiting the parties' relative rights and obligations under the
     Merger Agreement, in the event that the Company enters into an agreement
     (i) to consolidate with or merge into any person, other than Parent or one
     of its subsidiaries, and the Company shall not be the continuing or
     surviving corporation in such consolidation or merger, (ii) to permit any
     person, other than Subsidiary or one of Parent's other subsidiaries, to
     merge into the Company and the Company shall be the continuing or surviving
     corporation, but in connection with such merger, the shares of Company
     Common Stock outstanding immediately prior to the consummation of such
     merger shall be changed into or exchanged for stock or other securities of
     the Company or any other person or cash or any other property, or the
     shares of Company Common Stock outstanding immediately prior to the
     consummation of such merger shall, after such merger, represent less than
     50% of the outstanding voting securities of the merged company, or (iii) to
     sell or otherwise transfer all or substantially all of its assets to any
     person, other than Parent or one of its subsidiaries, then, and in each
     such case, the agreement governing such transaction shall make proper
     provision so that the Option shall, upon the consummation of any such
     transaction and upon the terms and conditions set forth herein, be
     converted into, or exchanged for, an option with identical terms
     appropriately adjusted to acquire the number and class of shares or other
     securities or property that Parent would have received in respect of
     Company Common Stock if the Option had been exercised immediately prior to
     such consolidation, merger, sale or transfer, or the record date therefor,
     as applicable.


                                      B-9
<PAGE>
 
(c)  If, prior to the termination of the Option in accordance with Section 2 or
     the Notice Date, the Company enters into any agreement pursuant to which
     all outstanding shares of Company Common Stock are to be purchased for, or
     converted into the right to receive in whole or in part (other than in
     respect of fractional shares), cash (a "Transaction"), the Company
     covenants that proper provision shall be made in such agreement to provide
     that, if the Option shall not therefore have been exercised, then upon the
     consummation of a Transaction (which in the case of a Transaction involving
     a tender offer shall be when shares of Company Common Stock are accepted
     for payment), Parent shall receive in exchange for the cancellation of the
     Option an amount in cash equal to the Cash Consideration and if proper
     provision is so made the Option shall be cancelled.  For purposes of this
     Agreement, the term "Cash Consideration" means the number of Option Shares
     multiplied by the difference between (A) the closing market price per share
     of Company Common Stock on the day immediately prior to the consummation of
     a Transaction and (B) the Purchase Price.

(d)  Whenever the number of Option Shares purchasable upon exercise hereof is
     adjusted as provided in this Section 9, the Purchase Price shall be
     adjusted by multiplying the Purchase Price by a fraction, the numerator of
     which shall be equal to the number of shares of Company Common Stock
     purchasable prior to the adjustment and the denominator of which shall be
     equal to the number of shares of Company Common Stock purchasable after the
     adjustment.

10.  Exchange Loss or Mutilation.  This Agreement (and the Option granted
     ---------------------------                                         
hereby) are exchangeable, without expense, at the option of the Parent, upon
presentation and surrender of this Agreement at the principal office of the
Company, for other agreements providing for Options of different denominations
entitling the Parent to purchase, on the same terms and subject to the same
conditions as are set forth herein, in the aggregate the same number of Option
Shares hereunder.  The terms "Stock Option Agreement" and "Option" as used
herein include any Stock Option Agreements and related options for which this
Agreement (and the Option granted hereby) may be exchanged.  Upon receipt by the
Company of evidence reasonably satisfactory to it of the loss, theft,
destruction or mutilation of this Agreement, and (in the case of loss, theft or
destruction) of reasonably satisfactory indemnification, and upon surrender and
cancellation of this Agreement, if mutilated, the Company shall execute and
deliver a new Agreement of like tenor and date.  Any such new Agreement executed
and delivered shall constitute an additional contractual obligation on the part
of the Company, whether or not the Agreement so lost, stolen, destroyed or
mutilated shall at any time be enforceable by anyone.

11.  Certain Covenants of the Company.  The Company agrees:  (i) that it shall
     --------------------------------                                         
at all times maintain, free from preemptive rights, sufficient authorized but
unissued or treasury shares of Common Stock so that the Option may be exercised
without additional authorization of Common Stock after giving effect to all
other options, warrants, convertible securities and other rights to purchase
Company Common Stock; (ii) that it will not, by charter amendment or through
reorganization, consolidation, merger, dissolution or sale of assets, or by any
other voluntary act, avoid or seek to avoid the observance or performance of any
of the covenants, stipulations or conditions to be observed or performed
hereunder by the Company; (iii) promptly to take all action as may from time to
time be required (including complying with all premerger


                                     B-10
<PAGE>
 
notification, reporting and waiting period requirements specified in 15 U.S.C.
Section 18a and regulations promulgated thereunder or to any other governmental
entity is necessary before the Option may be exercised, cooperating fully with
the Parent in preparing such applications or notices and providing such
information to each such governmental entity as they may require) in order to
permit the Parent to exercise the Option and the Company duly and effectively to
issue Option Shares pursuant hereto; and (iv) to take all action provided herein
to protect the rights of the Parent against dilution.

12.  Specific Performance.  The Company acknowledges that if the Company fails
     --------------------                                                     
to perform any of its obligations under this Agreement immediate and irreparable
harm or injury would be caused to Parent for which money damages would not be an
adequate remedy.  In such event, the Company agrees that Parent shall have the
right, in addition to any other rights it may have, to specific performance of
this Agreement.

13.  Profit Limitation.  (a) Notwithstanding any other provision of this
     -----------------                                                  
Agreement, in no event shall Parent's Total Profit (as hereinafter defined)
exceed $24 million (the "Cap") and, if it otherwise would exceed such amount,
Parent, at its sole election, shall either (a) deliver to the Company for
cancellation Shares previously purchased by Parent (valued at the average of the
last sales price for Company Common Stock for the ten trading days ending on the
day immediately preceding such delivery), (b) pay cash to the Company or (c)
undertake any combination thereof, so that Parent's Total Profit shall not
exceed the Cap after taking into account the foregoing actions.

          As used herein, the term "Total Profit" shall mean the aggregate
amount (before taxes) of the following: (i) the amount of cash paid or payable
by Parent pursuant to Section 7.1(b) of the Merger Agreement, (ii) (x) the
amount paid or payable by Parent pursuant to the Company's repurchase of Option
Shares pursuant to Section 7 hereof, less (y) Parent's purchase price for such
Option Shares, and (iii) (x) the net cash amounts received by Parent pursuant to
the sale of Option Shares (or any other securities into which such Option Shares
are converted or exchanged) to any unaffiliated party, less (y) Parent's
purchase price for such Option Shares.

14.  Miscellaneous.
     ------------- 

(a)  Expenses.  Except as otherwise provided in the Sections 6 and 7, each of
     --------                                                                
     the parties hereto shall bear and pay all costs and expenses incurred by it
     or on its behalf in connection with the transactions contemplated
     hereunder, including fees and expenses of its own financial consultants,
     investment bankers, accountants and counsel.

(b)  Waiver and Amendment.  Any provision of this Agreement may be waived at any
     --------------------                                                       
     time by the party that is entitled to the benefits of such provision, but
     such waiver shall only be effective if in writing and signed by the party
     entitled to the benefits of such provision.  This Agreement may not be
     amended, except by an instrument in writing signed on behalf of each of the
     parties.  The failure of any party to this Agreement to assert any of its
     rights under this Agreement or otherwise shall not constitute a waiver of
     such rights.


                                     B-11
<PAGE>
 
(c)  Descriptive Headings.  The descriptive headings contained herein are for
     --------------------                                                    
     convenience of reference only and shall not affect in any way the meaning
     or interpretation of this Agreement.

(d)  Entire Agreement; No Third-Party Beneficiaries.  Except as otherwise
     ----------------------------------------------                      
     provided, in this Agreement, the Merger Agreement (including the documents
     and instruments referred to therein), the Confidentiality Agreement by and
     between the Company and Parent, dated May 27, 1998, the Supplement to the
     Confidentiality Agreement by and between the Company and Parent, dated May
     6, 1998 and that certain Reciprocal Confidentiality Agreement by and
     between the Company and Parent (i) constitute the entire agreement, and
     supersede all prior agreements and understandings, both written and oral,
     between the parties with respect to the subject matter of this Agreement,
     and (ii) not intended to confer upon any person other than the parties any
     rights or remedies.  If any term, provision, covenant, or restriction of
     this Agreement is held by a court of competent jurisdiction or a federal or
     state regulatory agency to be invalid, void, or unenforceable, the other
     terms, provisions, covenants, and restrictions of this Agreement shall
     remain in full force and effect and shall not be affected, impaired, or
     invalidated.  If for any reason such court or regulatory agency determines
     that the Option does not permit Parent to acquire, or does not require the
     Company to repurchase, the full number of Option Shares provided herein (as
     adjusted pursuant to Section 9), it is the express intention of the Company
     to allow Parent to acquire, or to require the Company to repurchase, such
     lesser number of shares as may be permissible without any amendment or
     modification hereof.

(e)  GOVERNING LAW.  This Agreement shall be governed by and construed in
     -------------                                                       
     accordance with the laws of the State of Delaware (regardless of the laws
     that might otherwise govern under applicable Delaware principles of
     conflicts of law).  Each of the parties hereto waives any right to trial by
     jury with respect to any claim or proceeding related to or arising out of
     this Agreement or any of the transactions contemplated hereby.  THE GRANTOR
     AGREES THAT, IN CONNECTION WITH ANY LEGAL SUIT OR PROCEEDING ARISING WITH
     RESPECT TO THIS AGREEMENT, IT SHALL SUBMIT TO THE JURISDICTION OF THE
     UNITED STATES DISTRICT COURT FOR THE DISTRICT OF DELAWARE AND AGREES TO
     VENUE IN SUCH COURTS.  THE GRANTOR HEREBY APPOINTS THE SECRETARY OF THE
     GRANTOR AS ITS AGENT FOR SERVICE OF PROCESS FOR PURPOSES OF THE FOREGOING
     SENTENCE ONLY.

(f)  Notices.  All notices, requests, claims, demands and other communications
     -------                                                                  
     under this Agreement must be in writing and shall be deemed given if
     delivered personally, telecopied (which is confirmed) or sent by overnight
     courier (providing proof of delivery) to the parties at the following
     addresses (or at such other address for a party as shall be specified by
     like notice):


                                     B-12
<PAGE>
 
          (i)  if to Company, to:


               Penederm Incorporated
               320 Lakeside Drive
               Foster City, California 94404


               Telecopy No.:  (650) 358-0547


               Attention:  Lloyd H. Malchow
                           President & Chief Executive Officer

               with copies to:


               Heller Ehrman White & McAuliffe
               525 University Avenue
               Palo Alto, CA  94301-1300


               Telecopy No.:  (650) 324-0638


               Attention:  Henry Lesser; and

          (ii) if to Parent, to:


               Mylan Laboratories Inc.
               781 Chestnut Ridge Road
               P.O. Box 4310
               Morgantown, WV  26505


               Telecopy No.:  (304) 599-7284


               Attention:  Roderick P. Jackson
                           Senior Vice President

               with a copy to:


               Buchanan Ingersoll Professional Corporation
               One Oxford Centre
               301 Grant Street, 20th Floor
               Pittsburgh, PA  15219-1420


               Telecopy No.:  (412) 562-1041


               Attention:  JoEllen Lyons/John R. Previs


                                     B-13
<PAGE>
 
(g)  Counterparts.  This Agreement and any amendments hereto may be executed in
     ------------                                                              
     two counterparts, each of which shall be considered one and the same
     agreement and shall become effective when both counterparts have been
     signed by each of the parties and delivered to the other party, it being
     understood that both parties need not sign the same counterparts.

(h)  Assignment.  Neither this Agreement nor any of the rights, interests or
     ----------                                                             
     obligations hereunder or under the Option shall be assigned by any of the
     parties hereto (whether by operation of law or otherwise) without the prior
     written consent of the other party except that Parent may assign this
     Agreement and its rights hereunder to any of its subsidiaries.  Subject to
     the preceding sentence, this Agreement shall be binding upon, inure to the
     benefit of and be enforceable by the parties and their respective
     successors and assigns.

(i)  Further Assurances.  In the event of any exercise of the Option by Parent,
     ------------------                                                        
     the Company and Parent shall execute and deliver all other documents and
     instruments and take all other actions that may be reasonably necessary in
     order to consummate the transactions provided for by such exercise.

     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
signed by their respective officers thereunto duly authorized as of the day and
year first written above.

                              PENEDERM INCORPORATED



                              By: /s/ Lloyd H. Malchow
                                  -----------------------------------
                                  Lloyd H. Malchow
                                  President and Chief Executive Officer


                              MYLAN LABORATORIES INC.



                              By: /s/ Roderick P. Jackson
                                  -----------------------------------
                                  Roderick P. Jackson
                                  Senior Vice President


                                     B-14
<PAGE>

 
                                   APPENDIX C


                               VOTING AGREEMENTS




















<PAGE>


                                VOTING AGREEMENT

          VOTING AGREEMENT, dated as of June 24, 1998, between Mylan
Laboratories Inc., a Pennsylvania corporation ("Parent"), and the persons listed
on Schedule A hereto (individually, a "Stockholder" and collectively, the
"Stockholders").

          WHEREAS, Parent and Penederm Incorporated, a Delaware corporation (the
"Company"), propose to enter into an Agreement and Plan of Merger, dated the
date hereof (as the same may be amended or supplemented, the "Merger Agreement")
providing for the merger of MLI Acquisition Corp., a Delaware corporation and
wholly-owned subsidiary of Parent ("Subsidiary"), with the Company (the
"Merger");

          WHEREAS, each Stockholder is the record and beneficial owner of the
number of shares of common stock, par value $.01 per share, of the Company (the
"Company Common Stock") set forth opposite such Stockholder's name on Schedule A
hereto; such securities, as they may be adjusted by stock dividend, stock split,
recapitalization, combination or exchange of shares, merger, consolidation,
reorganization or other change or transaction of or by the Company, together
with securities that may be acquired after the date hereof by such Stockholder,
including Company Common Stock issuable upon the exercise of options to purchase
Company Common Stock (as the same may be adjusted as aforesaid), being
collectively referred to herein as the "Securities"; and

          WHEREAS, as a condition to their willingness to enter into the Merger
Agreement, Parent and Subsidiary have requested that the Stockholders enter into
this Agreement (capitalized terms not otherwise defined herein shall have the
meanings set forth in the Merger Agreement);

          NOW, THEREFORE, to induce Parent and Subsidiary to enter into, and in
consideration of them entering into, the Merger Agreement, and in consideration
of the premises and the representations, warranties and agreements contained
herein and intending to be legally bound hereby, the parties hereby agree as
follows:

1.  COVENANTS OF THE STOCKHOLDERS.  Each Stockholder, severally and not jointly,
agrees as follows:

(a)  Each Stockholder shall not, except as contemplated by the terms of this
     Agreement, (i) sell, transfer, pledge, assign or otherwise dispose of, or
     enter into any agreement, option or other arrangement (including any profit
     sharing arrangement) or understanding with respect to the sale, transfer,
     pledge, assignment or other disposition of, the Securities to any person
     other than Parent or Parent's designee, (ii) enter into any voting
     arrangement, whether by proxy, voting agreement, voting trust, power-of-
     attorney or otherwise, with respect to the Securities or (iii) take any
     other action that would in any way restrict, limit or interfere with the
     performance of its obligations hereunder or the transactions contemplated


                                      C-1
<PAGE>
 
     hereby; provided, however, that any Stockholder that is an individual may
     transfer all or any part of his or her Securities to any sibling or any
     other member of his or her immediate family, any of his or her lineal
     descendants or any trust for the benefit of any of them, if the recipient
     of the Securities agrees in advance in writing delivered to Parent to be
     bound by this Agreement.

(b)  Until the Merger is consummated or the Merger Agreement is terminated, the
     Stockholder shall not, nor shall the Stockholder permit any investment
     banker, financial adviser, attorney, accountant or other representative or
     agent acting on behalf of or at the direction of the Stockholder (a
     "Stockholder Representative") to, directly or indirectly (i) solicit,
     initiate or encourage (including by way of furnishing information), or take
     any other action designed or reasonably likely to facilitate, any inquiries
     or the making of any proposal which constitutes, or may reasonably be
     expected to lead to, any Takeover Proposal (as defined in the Merger
     Agreement) or (ii) participate in any discussions or negotiations regarding
     any Takeover Proposal. Without limiting the foregoing, it is understood
     that any violation of the restrictions set forth in the preceding sentence
     by a Stockholder Representative shall be deemed to be a violation of this
     Section 1(b) by the Stockholder.

(c)  At any meeting of stockholders of the Company called to vote upon the
     Merger and the Merger Agreement or at any adjournment thereof or in any
     other circumstances upon which a vote, consent or other approval (including
     by written consent) with respect to the Merger and the Merger Agreement is
     sought from the stockholders of the Company, each Stockholder shall,
     including by initiating a written consent solicitation if requested by
     Parent, vote (or cause to be voted) such Stockholder's Securities in favor
     of approving the Merger, the adoption of the Merger Agreement and the
     approval of the other transactions contemplated by the Merger Agreement and
     the calling of a special meeting of the stockholders of the Company to
     consider any of the foregoing.  At any meeting of stockholders of the
     Company or at any adjournment thereof or in any other circumstances upon
     which the Stockholder's vote, consent or other approval is sought, such
     Stockholder shall vote (or cause to be voted) such Stockholder's Securities
     against (i) any merger agreement or merger (other than the Merger Agreement
     and the Merger), consolidation, combination, sale or license of substantial
     assets, reorganization, recapitalization, dissolution, liquidation or
     winding up of or by the Company or any other Takeover Proposal (as defined
     in the Merger Agreement) (collectively, "Alternative Transactions"), or
     (ii) any amendment of the Company's Certificate of Incorporation or by-laws
     or other proposal or transaction involving the Company or any of its
     subsidiaries or any motion at a meeting of stockholders of the Company,
     which amendment or other proposal or transaction or motion would in any
     manner impede, frustrate, prevent or nullify, the Merger, the Merger
     Agreement or any of the other transactions contemplated by the Merger
     Agreement including any consent to the treatment of any Securities in or in
     connection with such transaction (collectively, "Frustrating
     Transactions").

2.   GRANT OF IRREVOCABLE PROXY COUPLED WITH AN INTEREST; APPOINTMENT OF PROXY.

(a)  Each Stockholder hereby irrevocably grants to, and appoints, any individual
     who shall be designated by Parent, and each of them, such Stockholder's
     proxy and


                                      C-2
<PAGE>
 
     attorney-in-fact (with full power of substitution), for and in the name,
     place and stead of such Stockholder, to vote such Stockholder's Securities,
     or grant a consent or approval in respect of such Securities, at any
     meeting of stockholders of the Company or at any adjournment thereof or in
     any other circumstances upon which their vote, consent or other approval is
     sought, (i) in favor of the Merger, the adoption by the Company of the
     Merger Agreement and the approval of the other transactions contemplated by
     the Merger Agreement and the calling of a special meeting of the
     stockholders of the Company to consider any of the foregoing, and (ii)
     against any Alternative Transaction or Frustrating Transaction.

(b)  Each Stockholder represents that any proxies heretofore given in respect of
     such Stockholder's Securities are not irrevocable, and that any such
     proxies are hereby revoked.

(c)  EACH STOCKHOLDER HEREBY AFFIRMS THAT THE PROXY SET FORTH IN THIS SECTION 2
     IS COUPLED WITH AN INTEREST AND IS IRREVOCABLE UNTIL SUCH TIME AS THIS
     AGREEMENT TERMINATES IN ACCORDANCE WITH ITS TERMS.  Such Stockholder hereby
     further affirms that such irrevocable proxy is given in connection with the
     execution of the Merger Agreement, and that such irrevocable proxy is given
     to secure the performance of the duties of such Stockholder under this
     Agreement.  Such Stockholder hereby ratifies and confirms all that the
     individual voting such irrevocable proxy may lawfully do or cause to be
     done by virtue hereof.  Such irrevocable proxy is executed and intended to
     be irrevocable in accordance with the provisions of Section 212 of the
     DGCL.  Such irrevocable proxy shall be valid until the later to occur of
     (i) one year from the date hereof or (ii) the termination of this Agreement
     in accordance with its terms.

3.  REPRESENTATIONS AND WARRANTIES OF THE STOCKHOLDERS.  Each Stockholder
hereby, severally and not jointly, represents and warrants to Parent as follows:

(a)  AUTHORIZATION.  The Stockholder has the legal capacity to execute, deliver
     and perform this Agreement.  This Agreement constitutes a valid and binding
     obligation of the Stockholder enforceable against the Stockholder in
     accordance with its terms.  If the Stockholder is married and the
     Securities constitute community property under applicable law, this
     Agreement has been duly authorized, executed and delivered by, and
     constitutes the valid and binding agreement of, the Stockholder's spouse
     enforceable against such spouse in accordance with its terms.

(b)  NO CONFLICT.  The execution, delivery and performance by the Stockholder of
     this Agreement and the consummation of the transactions contemplated hereby
     do not and will not (i) result in any breach or violation of or be in
     conflict with or constitute a default under any law or agreement or
     arrangement to which the Stockholder is a party or by which the Stockholder
     is bound, (ii) require any filing with or authorization by any governmental
     entity or (iii) require any consent or other action by any person under,
     constitute a default under, or give rise to any right of termination,
     cancellation or acceleration of a loss of any benefit to


                                      C-3
<PAGE>
 
     which the Stockholder is entitled under any provision of any agreement or
     other instrument binding on the Stockholder.

(c)  OWNERSHIP OF SECURITIES.  Each Stockholder's Securities and the
     certificates representing such Securities are now, and at all times during
     the term hereof will be, held by each Stockholder, or by a nominee or
     custodian for the benefit of such Stockholder, and the Stockholder has good
     and marketable title to such Securities, free and clear of any (i) liens,
     proxies, voting trusts or agreements, understandings or arrangements and
     (ii) pledges, restrictions, charges or other adverse claims of any kind or
     nature.  Each Stockholder owns of record or beneficially no securities of
     the Company, or any options, warrants or rights exercisable for securities
     of the Company, other than the Securities set forth opposite the
     Stockholder's name on Schedule A hereto.

(d)  MERGER AGREEMENT.  Each Stockholder understands and acknowledges that
     Parent and Subsidiary are entering into the Merger Agreement in reliance
     upon the Stockholder's execution and delivery of this Agreement.

4.  FURTHER ASSURANCES.  Each Stockholder will, from time to time, execute and
deliver, or cause to be executed and delivered, such additional or further
transfers, assignments, endorsements, consents and other instruments as Parent
may reasonably request for the purpose of effectively carrying out the
transactions contemplated by this Agreement and to vest the power to vote such
Stockholder's Securities as contemplated by Section 2.

5.  ASSIGNMENT; BINDING EFFECT.  Neither this Agreement nor any of the rights,
interests or obligations hereunder shall be assigned by any of the parties
hereto (whether by operation of law or otherwise) without the prior written
consent of the other parties.  Subject to the preceding sentence, this Agreement
shall be binding upon, inure to the benefit of, and be enforceable by, the
parties hereto and their respective successors and assigns.  Notwithstanding
anything contained in this Agreement to the contrary, nothing in this Agreement,
expressed or implied, is intended to confer on any person other than the parties
hereto or their respective heirs, successors, executors, administrators and
assigns any rights, remedies, obligations or liabilities under or by reason of
this Agreement.

6.  TERMINATION.  This Agreement, and all rights and obligations of the parties
hereunder, shall terminate upon the earliest to occur of the Effective Time or
the  termination of the Merger Agreement in accordance with its terms.  Nothing
in this Section 6 shall relieve any party from liability for willful breach of
this Agreement.

7.  STOP TRANSFER.  The Company agrees with, and covenants to, Parent that the
Company shall not register the transfer of any certificate representing any
Stockholder's Securities unless such transfer is made in accordance with the
terms of this Agreement.

8.  GENERAL PROVISIONS.

(a)  EXPENSES.  All costs and expenses incurred by Parent in connection with
     this Agreement and the transactions contemplated hereby shall be paid by

                                       
                                      C-4
<PAGE>
 
     Parent.  All costs and expenses incurred by the Stockholders in connection
     with this Agreement and the transactions contemplated hereby shall be paid
     by the Company.

(b)  AMENDMENTS.  This Agreement may not be amended except by an instrument in
     writing signed by each of the parties hereto.

(c)  NOTICE.  All notices and other communications hereunder shall be in writing
     and shall be deemed given upon receipt to the parties at the following
     addresses (or at such other address for a party as shall be specified by
     like notice):

                       (i)  if to Parent, to:

                            Mylan Laboratories Inc.
                            781 Chestnut Ridge Road
                             Post Office Box 4310
                             Morgantown, WV  26505
                        Telecopy Number (304) 599-7284

                                with a copy to:

                            John R. Previs, Esquire
                  Buchanan Ingersoll Professional Corporation
                               One Oxford Centre
                         301 Grant Street, 20th Floor
                          Pittsburgh, PA  15219-1410
                        Telecopy Number (412) 562-1041

and

                      (ii) if to a Stockholder, to the address set forth under 
the name of such Stockholder on Schedule A hereto:

                                with a copy to:

                             Henry Lesser, Esquire
                        Heller Ehrman White & McAuliffe
                             525 University Avenue
                           Palo Alto, CA  94301-1300
                        Telecopy Number (650) 324-0638

(d)  INTERPRETATION.  When a reference is made in this Agreement to a Section,
     such reference shall be to a Section of this Agreement unless otherwise
     indicated.  The headings contained in this Agreement are for reference
     purposes only and shall not affect in any way the meaning or interpretation
     of this Agreement.  Wherever the words "include", "includes" or "including"
     are used in this Agreement, they shall be deemed to be followed by the
     words "without limitation".


                                      C-5
<PAGE>
 
(e)  COUNTERPARTS.  This Agreement may be executed in two or more counterparts,
     all of which shall be considered one and the same agreement and shall
     become effective when two or more counterparts have been signed by each of
     the parties and delivered to the other parties, it being understood that
     all parties need not sign the same counterpart.

(f)  ENTIRE AGREEMENT; NO THIRD-PARTY BENEFICIARIES. This Agreement (including
     the documents and instruments referred to herein) (i) constitutes the
     entire agreement and supersedes all prior agreements and understandings,
     both written and oral, among the parties with respect to the subject matter
     hereof and (ii) is not intended to confer upon any person other than the
     parties hereto any rights or remedies hereunder.

(g)  GOVERNING LAW.  This Agreement shall be governed and construed in
     accordance with the laws of the State of Delaware without regard to any
     applicable conflicts of law.

9.  STOCKHOLDER CAPACITY.  As of the date of this Agreement, each of the
Stockholders is a director of the Company.  None of the Stockholders makes any
agreement or understanding herein in his or her capacity as a director or
officer of the Company.  Each Stockholder signs solely in his or her capacity as
the record holder and beneficial owner of, or the trustee of a trust whose
beneficiaries are the beneficial owners of, such Stockholder's Securities and
nothing herein shall limit or affect any actions taken by a Stockholder in his
or her capacity as an officer or director of the Company to the extent
specifically permitted by the Merger Agreement.

10.  ENFORCEMENT.  The parties agree that irreparable damage would occur in the
event that any of the provisions of this Agreement were not performed in
accordance with their specific terms or were otherwise breached.  It is
accordingly agreed that the parties shall be entitled to an injunction or
injunctions to prevent breaches of this Agreement and to enforce specifically
the terms and provisions of this Agreement in a court of the United States.
This being in addition to any other remedy to which they are entitled at law or
in equity.  In addition, each of the parties hereto waives any right to trial by
jury with respect to any claim or proceeding related to or arising out of this
Agreement or any of the transactions contemplated hereby.

EACH STOCKHOLDER AGREES THAT, IN CONNECTION WITH ANY LEGAL SUIT OR PROCEEDING
ARISING WITH RESPECT TO THIS AGREEMENT, IT SHALL SUBMIT TO THE JURISDICTION OF
THE UNITED STATES DISTRICT COURT FOR THE DISTRICT OF DELAWARE AND AGREES TO
VENUE IN SUCH COURTS.  EACH STOCKHOLDER HEREBY APPOINTS THE SECRETARY OF THE
COMPANY AS HIS OR HER  AGENT FOR SERVICE OF PROCESS FOR PURPOSES OF THE
FOREGOING SENTENCE ONLY.  EACH PARTY HERETO WAIVES ANY RIGHT TO JURY TRIAL IN
CONNECTION WITH ANY SUCH SUIT OR PROCEEDING.


                                      C-6
<PAGE>
 
          IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first written above.

                                    MYLAN LABORATORIES INC.


                                    By:    /s/ Roderick P. Jackson
                                        -------------------------------------
                                    Name:  Roderick P. Jackson
                                    Title: Senior Vice President

                                    STOCKHOLDERS

                                    
                                    /s/ Gerald Weinstein
                                    ----------------------------------
                                    Gerald Weinstein


                                    /s/ Marcia Weinstein
                                    ----------------------------------
                                    Marcia Weinstein


                                    /s/ David Collins
                                    ----------------------------------
                                    David Collins


                                    /s/ Harvey S. Sadow
                                    ----------------------------------
                                    Dr. Harvey S. Sadow, Ph.D.


                                    /s/Lloyd Malchow 
                                    ----------------------------------
                                    Lloyd Malchow


                                    /s/ Robert F. Allnutt
                                    ----------------------------------
                                    Robert F. Allnutt


                                    /s/ William E. Bergman
                                    ----------------------------------
                                    William E. Bergman


                                    /s/ Joseph E. Smith
                                    ----------------------------------
                                    Joseph E. Smith


                                      C-7
<PAGE>
 
                                   SCHEDULE A
                                   ----------

<TABLE>
<CAPTION>

STOCKHOLDER                                                          SECURITIES HELD
- ---------------------------------------------------------  ------------------------------------
<S>                                                        <C>
Gerald and Marcia Weinstein                                               27,725
c/o Penederm Incorporated
320 Lakeside Drive
Foster City, CA  94404
 
David Collins                                                             15,000
c/o Penederm Incorporated
320 Lakeside Drive
Foster City, CA  94404
 
Dr. Harvey S. Sadow, Ph.D.                                                10,000
c/o Penederm Incorporated
320 Lakeside Drive
Foster City, CA  94404
 
Lloyd Malchow                                                              7,840
c/o Penederm Incorporated
320 Lakeside Drive
Foster City, CA  94404
 
Robert F. Allnutt                                                          1,000
c/o Penederm Incorporated
320 Lakeside Drive
Foster City, CA  94404
 
William E. Bergman                                                             0
c/o Penederm Incorporated
320 Lakeside Drive
Foster City, CA  94404
 
Joseph E. Smith                                                                0
c/o Penederm Incorporated
320 Lakeside Drive
Foster City, CA  94404
</TABLE>


                                      C-8

<PAGE>
 
                                   APPENDIX D


                        OPINION OF LEHMAN BROTHERS INC.
































                                      D-1
<PAGE>
 
                          [Lehman Brothers Letterhead]


                                                                   June 23, 1998

Board of Directors
Penederm Incorporated
320 Lakeside Drive, Suite A
Foster City, California 94404

Members of the Board:

    We understand that Penederm Incorporated (the "Company") is proposing to
enter into an agreement with Mylan Laboratories, Inc. ("Mylan") pursuant to
which a subsidiary of Mylan ("Mylan sub") will merge with and into the Company
(the "Merger") and, upon effectiveness of the Merger, each share of the common
stock of the Company will be converted into the right to receive 0.68 shares
(the "Exchange Ratio") of Mylan common stock ("the Transaction").  The terms and
conditions of the Transaction are set forth in more detail in the Agreement and
Plan of Merger to be dated June 24, 1998 (the "Agreement") among the Company,
Mylan and Mylan sub.

    We have been requested by the Board of Directors of the Company to render
our opinion with respect to the fairness, from a financial point of view, to the
Company's stockholders of the Exchange Ratio to be offered to such stockholders
in the Transaction.  We have not been requested to opine as to, and our opinion
does not in any manner address, the Company's underlying business decision to
proceed with or effect the Transaction.

    In arriving at our opinion, we reviewed and analyzed: (1) the Agreement and
the specific terms of the Transaction, (2) the Company's annual report on Form
10-K for the year ended December 31, 1997 and such other publicly available
information concerning the Company and Mylan that we believe to be relevant to
our analysis, (3) financial and operating information with respect to the
business, operations, and prospects of the Company furnished to us by the
Company, (4) financial and operating information with respect to the business,
operations, and prospects of Mylan furnished to us by Mylan, (5) a trading
history of the Company's common stock over the last two years to the present,
and a comparison of that trading history with those of other companies that we
deemed relevant, (6) a trading history of Mylan's common stock over the last two
years to the present and a comparison of that trading history with those of
other companies that we deemed relevant, (7) a comparison of the historical
financial results and present financial condition of the Company with those of
other companies that we deemed relevant, (8) a comparison of the historical
financial results and present financial condition of Mylan with those of other
companies that we deemed relevant, (9) a comparison of the financial terms of
the Transaction with the financial terms of certain other transactions that we
deemed relevant, and (10) published estimates of third party research analysts
with respect to the future financial performance of Mylan.  In addition, we have
had discussions with the managements of the Company and Mylan concerning their
respective businesses, operations, assets, financial conditions, prospects and
operating synergies expected by such managements to result from the Transaction
and have undertaken such other studies, analyses and investigations as we deemed
appropriate.


                                      D-2
<PAGE>
 
Penederm Incorporated
June 23, 1998
Page Two

    In arriving at our opinion, we have assumed and relied upon the accuracy and
completeness of the financial and other information used by us without assuming
any responsibility for independent verification of such information and have
further relied upon the advice of managements of the Company and Mylan that they
are not aware of any facts or circumstances that would make such information
inaccurate or misleading.  With respect to the financial projections of the
Company, upon advice of the Company, we have assumed that such projections have
been reasonably prepared on a basis reflecting the best currently available
estimates and judgments of the management of the Company as to the future
financial performance of the Company and we relied upon such projections in
arriving at our opinion.  With respect to the future financial performance of
Mylan, upon advice of Mylan we have assumed that the published estimates of
third party research analysts are a reasonable basis upon which to evaluate the
future financial performance of Mylan.  In arriving at our opinion, we have not
conducted a physical inspection of the properties and facilities of the Company
or Mylan, and have not made or obtained any evaluations or appraisals of the
assets or liabilities of the Company.  In addition, you have not authorized us
to solicit, and we have not solicited, any indications of interest from any
third party with respect to the purchase of all or a part of the business of the
Company.  In addition, we have assumed that, as contemplated by the Agreement,
the Transaction will qualify as a reorganization within the meaning of Section
368(a) of the Internal Revenue Code of 1986, as amended, and therefore as a tax-
free transaction to the stockholders of the Company.  Our opinion necessarily is
based upon market, economic and other conditions as they exist on, and can be
evaluated as of, the date of this letter.

    Based upon and subject to the foregoing, we are of the opinion as of the
date hereof that, from a financial point of view, the Exchange Ratio to be
offered to the Company's stockholders in the Transaction is fair to such
stockholders.

    We have acted as financial advisor to the Company in connection with the
Transaction and will receive a fee for our services which is contingent upon the
consummation of the Transaction.  In addition, the Company has agreed to
indemnify us for certain liabilities that may arise out of the rendering of this
opinion.  In the ordinary course of our business, we may actively trade in the
equity securities of the Company and Mylan for our own account and for the
accounts of our customers and, accordingly, may at any time hold a long or short
position in such securities.

    This opinion is for the use and benefit of the Board of Directors of the
Company and is rendered to the Board of Directors in connection with its
consideration of the Transaction.  This opinion is not intended to be and does
not constitute a recommendation to any stockholder of the Company as to how such
stockholder should vote with respect to the Transaction.

                                    Very truly yours,

                                    LEHMAN BROTHERS

                                    By:   /s/ Ted Breck
                                        -------------------
                                        Managing Director


                                      D-3
<PAGE>
 
                                    PART II


                     INFORMATION NOT REQUIRED IN PROSPECTUS

Item 20. Indemnification of Directors and Officers.

   In accordance with the PBCL, Mylan's Bylaws provide that a director of Mylan
shall not be personally liable for monetary damages for any action taken, or any
failure to take any action, unless the director has breached or failed to
perform the duties required under Pennsylvania law and the breach or failure to
perform constitutes self-dealing, willful misconduct or recklessness.

   As permitted by PBCL, Mylan's Bylaws provide that directors and officers of
Mylan are indemnified under certain circumstances for expenses, judgments, fines
or settlements incurred in connection with suits and other legal proceedings.
The PBCL allows indemnification in cases where the person "acted in good faith
and in a manner he reasonably believed to be in, or not opposed to the best
interests of the corporation and, with respect to any criminal proceeding, had
no reasonable cause to believe his conduct was unlawful."

Item 21. Exhibits and Financial Statement Schedules.

   (a) Exhibits. The following is a list of Exhibits filed as part of this
Registration Statement.

<TABLE>
<CAPTION>

Exhibit No.                                                                         Reference
- -----------                                                                         ---------
<S>        <C>                                                          <C>         
2(a)       Merger Agreement (attached as Appendix A to the Proxy                  Filed herewith
           Statement/Prospectus included in this Registration
           Statement)
2(b)       Stock Option Agreement (attached as Appendix B to the                  Filed herewith
           Proxy Statement/Prospectus included in this Registration
           Statement)
3(a)       Amended and Restated Articles of Incorporation, as           Incorporated herein by reference
           amended, of Mylan                                            to Exhibit 3(a) to Mylan's Form
                                                                        10-Q for the quarter ended June
                                                                        30, 1992.
3(b)       Bylaws of Mylan                                              Incorporated herein by reference
                                                                        to Exhibit 3(b) to Mylan's Form
                                                                        10-Q for the quarter ended June
                                                                        30, 1992
5(a)       Opinion of Buchanan Ingersoll Professional Corporation                 Filed herewith
           regarding the validity of the Mylan Common Stock to be
           issued in the Merger
8(a)       Tax opinion of Heller Ehrman White & McAuliffe                    To be filed by Amendment
8(b)       Tax opinion of Buchanan Ingersoll Professional Corporation        To be filed by Amendment
23(a)(1)   Consent of Deloitte & Touche LLP                                       Filed herewith
23(a)(2)   Consent of Deloitte & Touche LLP                                       Filed herewith
23(b)      Consent of Ernst & Young LLP                                           Filed herewith
</TABLE>

                                      II-1



<PAGE>
 
<TABLE>
<CAPTION>

Exhibit No.                                                                         Reference
- -----------                                                                         ---------
<S>        <C>                                                          <C>         

23(c)      Consent of Buchanan Ingersoll Professional Corporation                 Filed herewith
           (included in Exhibit 5(a))
23(d)      Consent of Heller Ehrman White & McAuliffe (included in           To be filed by Amendment
           Exhibit 8(a))
23(e)      Consent of Buchanan Ingersoll Professional Corporation            To be filed by Amendment
           (included in Exhibit 8(b))
24(a)      Power of Attorney (appearing on signature page)                        Filed herewith
99(a)      Opinion of Lehman Brothers Inc. (attached as Appendix D to             Filed herewith
           the Proxy Statement/Prospectus included in this
           Registration Statement)
99(b)      Consent of Lehman Brothers Inc.                                        Filed herewith
99(c)      Penederm Form of Proxy for Common Stock                                Filed herewith
</TABLE>

   (b) Financial Statement Schedules. No financial statement schedules of the
Registrant are required to be included herein.

   (c) Opinions. The opinion of Lehman Brothers Inc. is included as Appendix D
to the Proxy Statement/Prospectus.


Item 22. Undertakings.

   (a) The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or 15(d) of the Exchange
Act (and, where applicable, each filing of an employee benefit plan's annual
report pursuant to Section 15(d) of the Exchange Act) that is incorporated by
reference in the Registration Statement shall be deemed to be a new registration
statement relating to the securities offered therein, and the offering of such
securities at that time shall be deemed to be the initial bona fide offering
thereof.

   (b) The undersigned Registrant hereby undertakes as follows: that prior to
any public reoffering of the securities registered hereunder through use of a
prospectus which is a part of this Registration Statement, by any person or
party who is deemed to be an underwriter within the meaning of Rule 145(c), the
issuer undertakes that such reoffering prospectus will contain the information
called for by the applicable registration form with respect to reofferings by
persons who may be deemed underwriters, in addition to the information called
for by the other Items of the applicable form.

   (c) The Registrant undertakes that every prospectus (i) that is filed
pursuant to paragraph (b) immediately preceding, or (ii) that purports to meet
the requirements of Section 10(a)(3) of the Securities Act and is used in
connection with an offering of securities subject to Rule 415, will be filed as
part of an amendment to the Registration Statement and will not be used until
such amendment is effective, and that, for purposes of determining any liability
under the Securities Act, each such post-effective amendment shall be deemed to
be a new registration statement relating to the securities offered therein, and
the offering of such securities at that time shall be deemed to be the initial
bona fide offering thereof.

   (d) Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers and controlling persons of the
Registrant pursuant to the foregoing provisions, or otherwise, the Registrant
has been advised that in the opinion of the Commission such indemnification is
against public policy as expressed in the Securities Act and is, therefore,
unenforceable. In the event that a claim for indemnification against such
liabilities (other than the payment by the Registrant of expenses incurred or
paid by a director, officer or controlling person of the Registrant in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate

                                      II-2
<PAGE>
 
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.

   (e) The undersigned Registrant hereby undertakes to respond to requests for
information that is incorporated by reference into the Proxy
Statement/Prospectus pursuant to Items 4, 10(b), 11 or 13 of this Form, within
one business day of receipt of such request, and to send the incorporated
documents by first class mail or other equally prompt means. This includes
information contained in documents filed subsequent to the effective date of the
Registration Statement through the date of responding to the request.

   (f) The undersigned Registrant hereby undertakes to supply by means of a
post-effective amendment all information concerning a transaction, and the
company being acquired involved therein, that was not the subject of and
included in the Registration Statement when it became effective.

   (g) The undersigned Registrant hereby undertakes:

       (1) To file, during any period in which offers or sales are being made, a
post-effective amendment to this registration statement:

          (A) To include any prospectus required by Section 10(a)(3) of the
Securities Act;

          (B) To reflect in the prospectus any facts or events arising after the
effective date of the registration statement (or the most recent post-effective
amendment thereof) which, individually or in the aggregate, represent a
fundamental change in the information set forth in the registration statement.
Notwithstanding the foregoing, any increase or decrease in volume of securities
offered (if the total dollar value of securities offered would not exceed that
which was registered) and any deviation from the low or high end of the
estimated maximum offering range may be reflected in the form of prospectus
filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the
changes in volume and price represent no more than a 20% change in the maximum
aggregate offering price set forth in the "Calculation of Registration Fee"
table in the effective registration statement; and

          (C) To include any material information with respect to the plan of
distribution not previously disclosed in the registration statement or any
material change to such information in the registration statement.

       (2) That, for the purpose of determining any liability under the
Securities Act of 1933, each such post-effective amendment shall be deemed to be
a new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

       (3) To remove from registration by means of a post-effective amendment
any of the securities being registered which remain unsold at the termination
of the offering.

                                      II-3
<PAGE>
 
                                   SIGNATURES

   Pursuant to the requirements of the Securities Act, the Registrant has duly
caused this Registration Statement to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of Pittsburgh, on 
August 20, 1998.

                              MYLAN LABORATORIES INC.

                              By:   /s/ Roderick P. Jackson
                                   -----------------------------
                                   Name:  Roderick P. Jackson
                                   Title:  Senior Vice President

   KNOW ALL MEN BY THESE PRESENTS, that each person whose signature appears
below constitutes and appoints Roderick P. Jackson and Donald C. Schilling, and
each of them individually, as his true and lawful attorney-in-fact and agent,
with full power of substitution and resubstitution, for him and in his name,
place and stead, in any and all capacities, to sign any and all amendments
(including post-effective amendments) to this Registration Statement, and any
subsequent registration statements pursuant to Rule 462 of the Securities Act
and to file the same, with all exhibits thereto, and other documents in
connection therewith, with the Securities and Exchange Commission, granting unto
said attorney-in-fact and agent, and each of them, full power and authority to
do and perform each and every act and thing requisite and necessary to be done
in and about the premises, as fully to all intents and purposes as he might or
could do in person, hereby ratifying and confirming all that said attorney-in-
fact or his substitute or substitutes, may lawfully do or cause to be done by
virtue hereof.

   Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed by the following persons in the capacities indicated
on August 20, 1998.


     Signatures                            Title
     ----------                            ----- 

/s/ Milan Puskar               Chairman, Chief Executive Officer, President,
- --------------------------     Director (Principal Executive Officer)
    Milan Puskar               

/s/ C.B. Todd  
- --------------------------     Senior Vice President and Director
    C.B. Todd                  

/s/ Dana G. Barnett   
- --------------------------     Executive Vice President and Director
    Dana G. Barnett                            

/s/ Patricia A. Sunseri
- --------------------------     Vice President--Investor and Public Relations
    Patricia A. Sunseri        and Director
                           
/s/ Robert W. Smiley
- --------------------------     Secretary and Director
    Robert W. Smiley           

/s/ Laurence S. DeLynn
- --------------------------     Director
    Laurence S. DeLynn         

/s/ John C. Gaisford, M.D.
- --------------------------     Director
    John C. Gaisford, M.D.     

/s/ Donald C. Shilling
- --------------------------     Chief Financial Officer (Principal Financial
    Donald C. Shilling         and Accounting Officer)
 

                                      II-4

<PAGE>
 
                                                                    Exhibit 5(a)

          [Letterhead of Buchanan Ingersoll Professional Corporation]
                                        
                                August 20, 1998
                                        



Mylan Laboratories Inc.
130 Seventh Street
1030 Century Building
Pittsburgh, Pennsylvania  15222

Ladies and Gentlemen:

     We have acted as special counsel to Mylan Laboratories Inc., a Pennsylvania
corporation (the "Company"), in connection with the Registration Statement on
Form S-4 (the "Registration Statement"), filed by the Company under the
Securities Act of 1933, as amended (the "Act"), relating to the registration
under the Act of up to 6,791,216 shares of the Company's common stock, par value
$0.50 per share (the "Shares"), to be issued in connection with the merger of
MLI Acquisition Corp., a Delaware corporation and wholly-owned subsidiary of the
Company ("Merger Sub"), and Penederm Incorporated, a Delaware corporation
("Penederm"), contemplated by the Agreement and Plan of Merger dated June 24,
1998 by and among Penederm, the Company and Merger Sub (the "Merger Agreement").

     In connection with this opinion, we have examined such corporate records,
certificates of public officials, and other documents, records and questions of
law as we have considered necessary or appropriate for the purposes of this
opinion.  In the examination of all documents we have assumed the genuineness of
all signatures and the authenticity of all documents submitted to us as
originals and the conformity to the original documents of all documents
submitted to us as certified of photostatic copies.

     Based upon and subject to the foregoing, we are of the opinion that the
Shares, when issued in accordance with the terms and conditions of the Merger
Agreement, will be validly issued, fully paid and non-assessable.

     This opinion is rendered solely to you in connection with the above-
referenced matter and may not be relied upon by you for any other purpose or
relied upon or furnished to any other person without our prior written consent.

     We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to this Firm under the caption
"Legal Matters" in the Proxy Statement/Prospectus constituting a part of the
Registration Statement.  In giving this consent,
<PAGE>
 
August 20, 1998
Page 2


we do not thereby admit that we come within the category of persons whose
consent is required under Section 7 of the Act or the rules and regulations of
the Securities and Exchange Commission thereunder.

                              Very truly yours,

                              BUCHANAN INGERSOLL PROFESSIONAL CORPORATION



                              By: /s/ James J. Barnes
                                 ---------------------------------------
                                 James J. Barnes

<PAGE>
                                                                Exhibit 23(a)(1)



                         INDEPENDENT AUDITORS' CONSENT


We consent to the incorporation by reference in this Registration Statement of 
Mylan Laboratories Inc. on Form S-4 of our report dated May 7, 1998,
incorporated by reference in the Annual Report on Form 10-K of Mylan
Laboratories Inc. for the year ended March 31, 1998 and to the reference to us
under the heading "Experts" in the Prospectus, which is part of this
Registration Statement.

/s/  Deloitte & Touche LLP

DELOITTE & TOUCHE LLP
Pittsburgh, Pennsylvania
August 19, 1998




<PAGE>
 
                                                                Exhibit 23(a)(2)




                         INDEPENDENT AUDITORS' CONSENT


We consent to the incorporation by reference in this Registration Statement of 
Mylan Laboratories Inc. on Form S-4 of our report dated February 4, 1998 
relating to the consolidated financial statements of Somerset Pharmaceuticals, 
Inc. and subsidiaries as of December 31, 1997 and 1996 and for each of the three
years in the period ended December 31, 1997, appearing in the Annual Report on 
Form 10-K of Mylan Laboratories Inc. for the year ended March 31, 1998 and to 
the reference to us under the heading "Experts" in the Prospectus, which is part
of this Registration Statement.

/s/  Deloitte & Touche LLP

DELOITTE & TOUCHE LLP
Pittsburgh, Pennsylvania
August 19, 1998




<PAGE>
 
                                                                   EXHIBIT 23(b)

               CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS

We consent to the reference to our firm under the caption "Experts" in the
Registration Statement (Form S-4) and related Proxy Statement of Penederm
Incorporated ("Penederm") and Prospectus of Mylan Laboratories Inc. and to the
incorporation by reference therein of our report dated January 27, 1998 with
respect to the consolidated financial statements of Penederm included in its
Annual Report (Form 10-K) for the year ended December 31, 1997, filed with the
Securities and Exchange Commission.



/s/ Ernst & Young LLP
Palo Alto, California
August 18, 1998

<PAGE>
                                                                   Exhibit 99(b)

                        CONSENT OF LEHMAN BROTHERS INC.

                         [Lehman Brothers Letterhead]



     We hereby consent to the use of our opinion letter dated June 23, 1998 to 
the Board of Directors of Penederm Incorporated ("Penederm"), included as 
Appendix D to the Proxy Statement of Penederm and Prospectus of Mylan 
Laboratories Inc. ("Mylan") which form part of the Registration Statement on 
form S-4 relating to the proposed merger of Penederm and Mylan and to the 
references therein to such opinion under the captions "THE MERGER-Opinion of 
Penederm's Financial Advisor."

     In giving such consent, we do not admit that we come within the category of
persons whose consent is required under Section 7 of the Securities Act of 
1933, as amended (the "Securities Act"), or the rules and regulations of the 
Securities and Exchange Commission (the "Commission") thereunder, nor do we 
admit that we are experts with respect to any part of such Registration 
Statement within the meaning of the term "experts" as used in the Securities Act
or the rules and regulations of the Commission thereunder.


                                                 LEHMAN BROTHERS INC.


                                                 By:  /s/ Ted Breck
                                                    ---------------------------
                                                      Ted Breck
                                                      Managing Director


August 20, 1998

<PAGE>
 
                                                                   Exhibit 99(c)

                                [Form of Proxy]
                                        
 
 
P R O X Y
 
                             PENEDERM INCORPORATED
                                       
                   PROXY for Special Meeting of Stockholders
 
                        To Be Held _____________, 1998
 
          THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS
 
     The undersigned stockholder of PENEDERM INCORPORATED, a Delaware
corporation, hereby acknowledges receipt of the Notice of Special Meeting of
Stockholders and Proxy Statement/Prospectus, each dated ______________, 1998,
and hereby appoints Lloyd H. Malchow and Michael A. Bates, and each of them,
proxies and attorneys-in-fact, with full power to each of substitution, on
behalf of the undersigned, to represent the undersigned at the Special Meeting
of Stockholders of Penederm Incorporated to be held at the Westin Hotel - San
Francisco Airport, at ________ a.m., local time on ______________, 1998, and at
all adjournments or postponements thereof, and to vote shares of Common Stock
that the undersigned would be entitled to vote if then and there personally
present, on all matters set forth on the reverse side hereof.

     THE SHARES REPRESENTED BY THIS PROXY WILL BE VOTED IN ACCORDANCE WITH THE
SPECIFICATIONS MADE HEREIN. IF NO SPECIFICATION IS INDICATED, THE SHARES
REPRESENTED BY THIS PROXY WILL BE VOTED FOR EACH OF THE PROPOSALS ON THE REVERSE
SIDE HEREOF.

                  CONTINUED AND TO BE SIGNED ON REVERSE SIDE
 



                                                                  SEE REVERSE
                                                                      SIDE
 
 
 
<PAGE>
 
                                                         [X] Please mark votes
                                                             as in this example



THE BOARD OF DIRECTORS RECOMMENDED A VOTE "FOR" THE FOLLOWING PROPOSAL:
 
                                                      For  Against  Abstain
PROPOSAL:  To approve and adopt the                   [ ]    [ ]      [ ]
           Agreement and Plan of
           Merger, dated June 24, 1998,
           by and among Penederm Incorporated
           ("Penederm"), Mylan Laboratories
           Inc. ("Mylan") and MLI Acquisition
           Corp. and the transactions contemplated
           thereby.
 
OTHER BUSINESS:
           In their discretion, the proxy holders
           are hereby authorized to vote on such
           other business as may properly come
           before the Special Meeting, including,
           among other things, a motion to adjourn
           the Special Meeting to another time and/or
           place for, among other things, the purpose
           of soliciting additional proxies.


                                     MARK HERE FOR    [ ]
                                     ADDRESS CHANGE
                                     AND NOTE AT LEFT
                                     Note: Please sign exactly as your name
                                     appears on your stock certificate. If the
                                     stock is registered in the names of two or
                                     more persons, each should sign. Executors,
                                     administrators, trustees, guardians,
                                     attorneys and corporate officers should
                                     insert their titles.
 
The undersigned acknowledges receipt of the Notice of Special Meeting and 
Proxy Statement/Prospectus dated ______, 1998.
 
Signature(s) _______________________________________________    Date __________

NOTE:  Please mark, sign, and date and return the proxy card promptly using 
the enclosed envelope.


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