CUBIST PHARMACEUTICALS INC
10-K, 1999-03-17
PHARMACEUTICAL PREPARATIONS
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                UNITED STATES SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                                   FORM 10-K
                 FOR ANNUAL AND TRANSITION REPORTS PURSUANT TO
           SECTION 13 OR 15(D) OF THE SECURITIES EXCHANGE ACT OF 1934
 
  /X/    ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE SECURITIES
         EXCHANGE ACT OF 1934
 
                  For the fiscal year ended: DECEMBER 31, 1998
 
  / /    TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE
         SECURITIES EXCHANGE ACT OF 1934
 
          For the transition period from: ____________ to ____________
 
                        Commission file number: 0-21379
 
                          CUBIST PHARMACEUTICALS, INC.
             (Exact name of registrant as specified in its charter)
 
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<S>                                         <C>
                 DELAWARE                                   22-3192085
     (STATE OR OTHER JURISDICTION OF                     (I.R.S. EMPLOYER
      INCORPORATION OR ORGANIZATION)                   IDENTIFICATION NO.)
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                      24 EMILY STREET, CAMBRIDGE, MA 02139
             (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES AND ZIP CODE)
 
                                 (617) 576-1999
              (REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE)
 
          Securities registered pursuant to Section 12(b) of the Act:
                                      NONE
 
          Securities registered pursuant to Section 12(g) of the Act:
                         COMMON STOCK, $.001 PAR VALUE
                                (TITLE OF CLASS)
 
    Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes /X/  No / /
 
    Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-X is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K / /
 
    The aggregate market value of the registrant's common stock, $.001 par value
per share ("Common Stock"), held by non-affiliates of the registrant as of March
5, 1999 was approximately $40,418,517 based on 10,430,585 shares held by such
non-affiliates at the closing price of a share of Common Stock of $3.875 as
reported on the Nasdaq National Market on such date. Affiliates of the Company
(defined as officers, directors and owners of 10 percent or more of the
outstanding share of Common Stock) owned 7,019,871 shares of Common Stock
outstanding on such date. The number of outstanding shares of Common Stock of
the Company on March 5, 1999 was 17,450,456.
 
                      DOCUMENTS INCORPORATED BY REFERENCE
 
    Portions of the registrant's definitive Proxy Statement to be delivered to
stockholders in connection with the Annual Meeting of Stockholders to be held on
June 1, 1999 are incorporated by reference into Part III hereof. With the
exception of the portions of such Proxy Statement expressly incorporated into
this Annual Report on Form 10-K by reference, such Proxy Statement shall not be
deemed filed as part of this Annual Report on Form 10-K.
 
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                          CUBIST PHARMACEUTICALS, INC.
                           ANNUAL REPORT ON FORM 10-K
 
TABLE OF CONTENTS
 
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      ITEM                                                                                                            PAGE
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                                                                                                          PART I
 
         1   Business............................................................................................           3
         2   Description of Property.............................................................................          26
         3   Legal Proceedings...................................................................................          27
         4   Submission of Matters to a Vote of Security Holders.................................................          27
 
                                                                                                         PART II
 
         5   Market For Registrant's Common Stock and Related Stockholder Matters................................          28
         6   Selected Financial Data.............................................................................          30
         7   Management's Discussion and Analysis of Financial Condition and Results of Operations...............          30
        7A   Quantitative and Qualitative Disclosures About Market Risk..........................................          37
         8   Financial Statements................................................................................          38
         9   Changes in and Disagreements With Accountants on Accounting and Financial Disclosure................          61
 
                                                                                                        PART III
 
        10   Directors and Executive Officers of the Registrant..................................................          61
        11   Executive Compensation..............................................................................          61
        12   Security Ownership of Certain Beneficial Owners and Management......................................          61
        13   Certain Relationships and Related Transactions......................................................          61
 
                                                                                                         PART IV
 
        14   Exhibits, Financial Statement Schedules, and Reports on Form 8-K....................................          62
 
             Signatures..........................................................................................          67
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    EXCEPT FOR THE HISTORICAL INFORMATION CONTAINED HEREIN, THIS ANNUAL REPORT
ON FORM 10-K MAY CONTAIN "FORWARD-LOOKING STATEMENTS" WITHIN THE MEANING OF
SECTION 27A OF THE SECURITIES ACT OF 1933 AND SECTION 21E OF THE SECURITIES
EXCHANGE ACT OF 1934, INCLUDING, BUT NOT LIMITED TO, (I) STATEMENTS ABOUT THE
ADEQUACY OF THE COMPANY'S CASH, CASH EQUIVALENTS, OTHER CAPITAL RESOURCES,
INTEREST INCOME, OTHER INCOME AND FUTURE REVENUES DUE UNDER THE COMPANY'S
COLLABORATIVE AGREEMENTS TO FUND ITS OPERATING EXPENSES AND CAPITAL REQUIREMENTS
AS CURRENTLY PLANNED THROUGH 1999, (II) STATEMENTS ABOUT THE AMOUNT OF CAPITAL
EXPENDITURES THAT THE COMPANY EXPECTS TO INCUR IN 1999, AND (III) CERTAIN
STATEMENTS IDENTIFIED OR QUALIFIED BY WORDS SUCH AS "LIKELY", "WILL",
"SUGGESTS", "MAY", "WOULD", "COULD", "SHOULD", "EXPECTS", "ANTICIPATES",
"ESTIMATES", "PLANS", "PROJECTS", "BELIEVES", OR SIMILAR EXPRESSIONS (AND
VARIANTS OF SUCH WORDS OR EXPRESSIONS). INVESTORS ARE CAUTIONED THAT
FORWARD-LOOKING STATEMENTS ARE INHERENTLY UNCERTAIN. ACTUAL PERFORMANCE AND
RESULTS OF OPERATIONS MAY DIFFER MATERIALLY FROM THOSE PROJECTED OR SUGGESTED IN
THE FORWARD-LOOKING STATEMENTS DUE TO CERTAIN RISKS AND UNCERTAINTIES,
INCLUDING, BUT NOT LIMITED TO, THE RISKS AND UNCERTAINTIES DESCRIBED OR
DISCUSSED IN THE SECTION "RISK FACTORS" IN THIS ANNUAL REPORT ON FORM 10-K. THE
FORWARD-LOOKING STATEMENTS CONTAINED HEREIN REPRESENT THE COMPANY'S JUDGMENT AS
OF THE DATE OF THIS ANNUAL REPORT ON FORM 10K, AND THE COMPANY CAUTIONS READERS
NOT TO PLACE UNDUE RELIANCE ON SUCH STATEMENTS.
 
                                     PART I
 
ITEM 1. BUSINESS
 
THE COMPANY
 
    Cubist Pharmaceuticals, Inc. is a drug company focused on the discovery,
development and commercialization of novel drugs to treat infections.
Daptomycin, the Company's in-licensed lead product, is a unique agent with
bactericidal activity that addresses the critical need for new antibiotics with
potent activity against life threatening infections. The Company began Phase III
clinical trials of intravenous daptomycin for complicated skin and soft tissue
infections and also began a Phase II clinical trial for bacteremia in February
of 1999. Cubist is also applying its VITA-TM- technology to validate unique
targets and to build assays to identify additional novel compounds with a broad
spectrum of activity against life-threatening infectious organisms such as
methicillin resistant STAPHYLOCOCCUS AUREUS (MRSA) and vancomycin resistant
enterococci (VRE).
 
    The Company's business strategy for building a profitable and sustainable
pharmaceutical company involves building value from its core competencies of
generating and utilizing drug discovery and drug development technologies.
Daptomycin is currently the focal product in the Company's drug development
program. The Company at this time plans on independently developing daptomycin
within the United States and Europe, however, the Company will continue to
evaluate partnering opportunities for daptomycin. In addition, the Company has
built an experienced drug development team, developed
 
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development processes and plans to utilize these core strengths to develop
additional drug candidates. Such candidates are currently under evaluation for
future in-licensing opportunities.
 
    The fundamental technology used in the Company's drug discovery program is
its VITA-TM- (Validation IN VIVO of Targets and Assays for Antiinfectives)
technology. The Company believes that the VITA-TM- technology addresses an
immediate need within the arena of drug discovery. The Company also believes
that there is the potential for it to obtain revenues by granting non-exclusive
licenses to the technology through collaborations with multiple partners.
Consistent with this strategy, in February 1999, the Company entered into a
Collaborative Research and License Agreement with Novartis Pharma AG
("Novartis") pursuant to which the Company granted Novartis a non-exclusive
license to the VITA-TM- technology. In return, the Company received funds in the
form of an up front equity investment, and will receive revenue in the form of
research costs reimbursements, research and development milestone payments and
royalties on sales of drugs. In addition, the Company is still engaged in drug
discovery partnerships with Bristol-Myers Squibb Company ("Bristol-Myers
Squibb") and Merck & Co., Inc. ("Merck") utilizing technology unrelated to
VITA-TM-. These collaborations may also contribute future milestone payments to
help reduce the Company's expenditures.
 
OVERVIEW OF INFECTIOUS DISEASE AND DRUG RESISTANCE
 
    Infectious diseases are caused by bacteria and fungi present in the
environment that enter the body through the skin or mucous membranes of the
lungs, nasal passages or gastrointestinal tract, and overwhelm the body's immune
system. These pathogens then establish themselves in various tissues and organs
throughout the body and cause a number of serious and, in some cases, lethal
infections, including those of the bloodstream, skin and soft tissue, heart,
lung, liver and urinary tract.
 
    Antiinfective drugs have, in many cases, proven highly successful in
controlling the serious morbidity and mortality that accompany these infections.
These drugs work by chemically binding to specific targets in a bacterial or
fungal pathogen, thereby inhibiting a cell function essential to its survival.
Currently available antiinfective drugs can be divided into the following four
broad categories, according to the type of essential cell function they inhibit:
(i) protein synthesis (e.g., tetracyclines, macrolides and aminoglycosides),
(ii) cell wall and membrane synthesis (e.g., penicillins, cephalosporins,
carbapenems, glycopeptides and polyenes), (iii) nucleic acid synthesis (e.g.,
fluoroquinolones) and (iv) cell metabolism (e.g., trimethoprim, sulfonamides,
azoles and allylamines).
 
    Recently, there has been a rise in the incidence of infectious diseases
caused by bacteria and fungi that have developed resistance to existing
antiinfective drugs. This phenomenon has been well documented in the medical
literature. A number of serious pathogens such as STAPHYLOCOCCUS AUREUS,
STREPTOCOCCUS PNEUMONIAE, ENTEROCOCCUS FAECALIS, ENTEROCOCCUS FAECIUM,
ESCHERICHIA COLI, HAEMOPHILUS INFLUENZAE,
 
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PSEUDOMONAS AERUGINOSA, MYCOBACTERIUM TUBERCULOSIS, CANDIDA ALBICANS,
ASPERGILLUS FUMIGATUS AND ASPERGILLUS FLAVUS have shown significant evidence of
drug resistance.
 
    The increasing prevalence of antiinfective drug resistance is a natural
outcome of the use and overuse of antiinfective drugs. When bacteria or fungi
are exposed to an antiinfective drug, the drug kills or attenuates the growth of
the susceptible pathogen. However, any variant in the bacterial population that
has spontaneously undergone a genetic change that confers drug resistance will
have a selective growth advantage, which is known in evolutionary terms as
natural selection. Thus, the antiinfective drug does not technically cause the
resistance but creates a situation in which the resistant pathogen can multiply
in the presence of the drug, increasing the population approximately a
millionfold in a day and quickly becoming the predominant microorganism. These
resistant bacteria can then spread rapidly from the infected patient to healthy
individuals.
 
    Bacteria and fungi have evolved multiple resistance mechanisms against
currently available categories of antiinfective drugs. These mechanisms include:
(i) utilization of an enzyme to alter the drug's structure by creating or
destroying chemical bonds, (ii) modification of the cell membrane to block entry
of the drug, (iii) utilization of a protein to pump the drug out of their cells
before the drug binds to the target and (iv) alteration of the target to
significantly limit the ability of the antiinfective drug to bind to the target.
Bacteria and fungi change the target by mutation of the target's protein
sequence, by chemical modification of the target structure or by the acquisition
of a new gene from another pathogen that substitutes for the target function.
 
    Chemistry-based approaches have focused on chemically modifying the
molecular structure of existing antiinfective drugs or combining existing
antiinfective drugs with another agent (an antibiotic potentiator) to circumvent
established drug resistance mechanisms. Despite the introduction of second and
third generation antiinfective drugs, certain pathogens have developed
resistance to all currently available drugs. Examples include:
 
    (i) Methicillin resistant STAPHYLOCOCCUS AUREUS ("MRSA"): S. AUREUS is a
common bacterial pathogen causing skin infections and colonization of the nares
(entrance to the nose). It is also a frequent hospital-borne pathogen, and
routinely acquires characteristics of drug resistance, virulence and toxicity
through bacterial genetic transfer. MRSA strains can cause severe tissue damage
to existing wounds and bacteremia (blood-borne infections), which has a 42%
mortality rate.
 
    (ii) Vancomycin resistant enterococci ("VRE"): Vancomycin is regarded by
many medical practitioners as the "last line of defense" against virulent
Gram-positive bacteria species. The emergence of VRE strains in the 1990's has
led to infections for which no approved therapy exists. Vancomycin resistance is
found in both ENTEROCOCCUS FAECIUM and ENTEROCOCCUS FAECALIS. Nosocomial
(hospital based) VRE increased
 
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from 0.3% to 7.9%, and has continued to rapidly rise. Resulting VRE bacteremia
has a 40 - 55% mortality rate.
 
    (iii) Glycopeptide intermediately susceptible STAPHYLOCOCCUS AUREUS
("GISA"): The first reports of S. AUREUS infections with decreased
susceptibility to vancomycin therapy occurred in 1997. Such bacterial strains
have been found in a wide geographical area throughout Japan and North America.
Resistance progression from GISA is expected to be the emergence of fully drug
resistant S. AUREUS strains that the medical community has long feared.
 
DAPTOMYCIN
 
    In December 1998, the Company filed an Investigational New Drug ("IND")
Application with the U.S. Food and Drug Administration ("FDA") and began Phase
III clinical trials for intravenous daptomycin in February 1999. These pivotal
trials are designed to evaluate the safety and efficacy of daptomycin in
patients with complicated skin and soft tissue infections due to Gram-positive
bacteria. The observed advantages of daptomycin prior to such trials include its
rapidly bactericidal activity and effectiveness IN VITRO against all clinically
relevant Gram-positive bacterial strains, including drug resistant strains.
Daptomycin has a favorable side effect profile and is expected to be
administered as a once-a-day therapy. Cubist's IND also includes the initiation
of an open label Phase II trial in patients with bloodstream infections or
bacteremia. Bacteremia in hospitalized patients is a serious medical challenge
associated with high mortality. These Phase II trials also began in February
1999.
 
    Daptomycin is a novel cyclic lipopeptide antibiotic derived from a
fermentation process. It is rapidly bactericidal IN VITRO against all clinically
significant Gram-positive microorganisms including VRE, MRSA, GISA, and
coagulase negative staphylococci. In November 1997, Cubist obtained an exclusive
worldwide license to develop, manufacture and market daptomycin from Eli Lilly
and Company ("Lilly"). Previous Phase II studies conducted by Lilly exhibited
comparable efficacy to conventional therapy in treating skin and soft tissue
infections and bloodstream infections. Daptomycin has exhibited a highly
favorable safety profile as compared to conventional therapy. At higher dosages
than planned for any Cubist trials, a few subjects experienced reversible mild
skeletal muscle effects. No cardiac or smooth muscle abnormalities were
encountered. Additionally, results of Cubist's nonclinical investigations
suggest that once-a-day administration of daptomycin may be more effective than
a 12-hour dosing regimen and may obviate skeletal muscle abnormalities.
 
    In the years since the Phase II clinical studies were conducted by Lilly,
the need for additional therapies for Gram-positive infections has grown more
acute. Moreover, there has been an alarming increase in methicillin and
vancomycin-resistant Gram-positive pathogens, particularly in hospitalized
patients. Bacteremia caused by these organisms is associated with 40-55%
mortality, and alternative
 
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therapeutic modalities are urgently needed. On the basis of its IN VITRO
activity against clinically significant microorganisms, its bactericidal mode of
action, and its promising profile in Phase I and Phase II clinical trials, the
Company is undertaking further clinical evaluation of intravenous daptomycin for
the treatment of serious Gram-positive infections and bacteremia.
 
    Daptomycin exerts its antibacterial effect at the bacterial cytoplasmic
membrane and disrupts multiple aspects of membrane function, including
peptidoglycan synthesis, lipoteichoic acid synthesis, and the bacterial membrane
potential. Although not understood in detail, daptomycin's mechanism of
antimicrobial action is clearly distinct from that of other antibiotics,
including -lactams, aminoglycosides, glycopeptides, and macrolides. Daptomycin
demonstrates rapid concentration-dependent bactericidal activity against
enterococci and staphylococci, unlike the glycopeptides, vancomycin and
teicoplanin. Daptomycin exhibits a concentration-dependent post-antibiotic
effect of 1-6 hours on Gram-positive organisms IN VITRO. In a thigh soft tissue
infection model in mice, efficacy was primarily related to the peak serum
concentration of daptomycin.
 
    In February of 1998, the Company contracted with ACS Dobfar of Milan, Italy
to manufacture daptomycin for clinical trials. The Company received initial
delivery of Good Manufacturing Practices ("GMP") daptomycin for clinical trial
use in the fourth quarter of 1998.
 
THE CUBIST DISCOVERY PROGRAM
 
    The Company is developing and implementing novel technologies to accelerate
the process of drug discovery. To discover novel antiinfectives for clinical
development, the Cubist discovery platform integrates the scientific disciplines
and technologies required for target validation and assay development (including
Cubist's proprietary VITA-TM- technology), high-throughput screening and
medicinal chemistry. Cubist's VITA-TM- technology enhances the quality of leads
identified by screening target assays for antiinfectives. VITA-TM- generates
functional biology data useful for prioritizing the most valuable, protein
therapeutic targets from clinically important pathogens such as STAPHYLOCOCCUS
AUREUS. The technology allows validated targets to be enabled for high
throughput screens for the rapid identification of quality leads for medicinal
chemistry programs.
 
VITA-TM- (VALIDATION IN VIVO OF TARGETS AND ASSAYS FOR ANTIINFECTIVES)
 
    Because therapeutic targets are proteins, a functional biology approach to
validate the utility of a target protein for antiinfective inhibition is needed.
The genomics explosion has resulted in the identification of a wealth of
potential targets for drug discovery. Current methods to prioritize targets
utilize genomics to investigate the relevance of the gene encoding the target
(gene knockout studies) or the relevance of the expression of the gene encoding
the target (antisense, ribozyme or mRNA expression
 
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studies). These indirect methods do not assess the function of the target
protein during an infection. VITA-TM-, on the other hand, is designed to
directly validate target proteins for antiinfective inhibition in the pathogen
during an established infection in an animal and to identify whether or not a
compensatory mechanism can override the inhibition of an essential target during
an infection. In addition, the VITA-TM- technology enhances the quality of leads
identified by screening target assays for antiinfectives. VITA-TM- is designed
to generate functional biology data useful for prioritizing valuable, protein
therapeutic targets from clinically relevant pathogens such as STAPHYLOCOCCUS
AUREUS. The technology enables validated targets high throughput screens for the
rapid identification of quality leads for medicinal chemistry programs.
 
    An antiinfective drug acts during an infection by binding to a specific
target and inhibiting its function. Target inhibition leads to impaired pathogen
growth or cell death and reduced infectivity; consequently the animal survives
the infection. Utilizing VITA-TM-, a target is validated by first regulating the
expression of a peptide that binds to a functionally relevant site of the target
during an established infection in mice. If the target is essential for pathogen
survival and continued infectivity, then the peptide will inhibit target
function and pathogen growth and the mice will survive. If the inhibition of the
target is not relevant to infectivity, the pathogen will continue to thrive and
the mice will die from the infection. The peptide used to specifically inhibit
the target can then be used in a high throughput screen to identify small
molecule compounds that bind to functionally relevant sites on the target
protein by competing with the peptide for binding.
 
    VITA-TM- couples the validation of antiinfective targets during an
established infection in a mouse model system with assay development to discover
novel drug leads that act on therapeutically relevant targets. The method by
which targets are validated by the VITA-TM- technology is analogous to how an
antibiotic inhibits its protein target during an established infection. The
assay developed using the VITA-TM-technology is more likely to be broadly
applicable to any target, including proteins encoded by open reading frames
(ORFs) than using other known technologies. ORFs present opportunities for drug
discovery and until recently have been intractable to traditional high
throughput screening paradigms. Because quality, small molecule lead compounds
that bind to functionally relevant sites on validated targets are identified via
high throughput screening to form the basis of medicinal chemistry programs, the
Company believes the VITA-TM- technology will enhance the antiinfective drug
discovery process by enabling the identification of such ORFs. The goal of using
the VITA-TM- technology is to focus the ensuing medicinal chemistry programs on
therapeutically relevant targets potentially resulting in resource and cost
savings throughout the discovery and development process.
 
    Cubist has established scientific proof of principle of the VITA-TM-
technology and has established a variety of methodologies to expeditiously
implement this technology for drug discovery including the rapid identification
and characterization of specific peptides, methods for the regulation of
expression of the
 
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peptides in pathogenic organisms during infection, a murine model of infection
and a high throughput competitive binding assay applicable to many diverse
targets. The continued enhancement and licensing of the VITA-TM- technology is
the primary focus of Cubist's discovery program. Patent applications have been
filed.
 
HIGH THROUGHPUT SCREENING
 
    Cubist utilizes state of the art technologies in automation, robotics and
assay technologies to perform high-throughput screening of compound libraries to
identify novel inhibitors. Thousands of compounds a day may be screened in these
assays. Inhibitors may be further characterized using Cubist's secondary
screening assays where increasingly stringent selection criteria are applied to
identify drug candidates with the greatest potential for successful development.
 
MEDICINAL CHEMISTRY
 
    Cubist optimizes the pharmaceutical properties of lead compounds through the
iterative use of medicinal chemistry and IN VITRO biological assays. The
Company's medicinal chemistry efforts are directed towards increasing the
throughput of synthesis of optimized analogues of specific lead compounds
utilizing chemical technologies including focused arrays, combinatorial
libraries and computational chemistry. Lead compounds enter a high-speed
chemical analoging program which generates large numbers of structurally-related
compounds. Analogs are evaluated for numerous biological properties.
 
COLLABORATIVE AGREEMENTS
 
    The Company has entered into drug discovery and development collaboration
agreements with Novartis Pharma AG ("Novartis"), Bristol-Myers Squibb Company
("Bristol-Myers Squibb") and Merck & Co., Inc. ("Merck") to discover and develop
novel antiinfectives. In the Bristol-Myers Squibb and Merck collaborations, the
collaborators' respective compound libraries have been screened against certain
Cubist aminoacyl-tRNA synthetase targets. Chemical compound structures are
currently undergoing optimization into pre-clinical and clinical development
candidates. In the Novartis collaboration, the Company will validate and develop
assays for antiinfective targets utilizing the Company's proprietary VITA-TM-
technology and to identify new compounds for development as antiinfectives.
These collaborations have provided the Company with funding, research and
development resources, and access to libraries of diverse compounds and clinical
development, manufacturing and commercialization capabilities.
 
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    BRISTOL-MYERS SQUIBB
 
    In June 1996, Cubist and Bristol-Myers Squibb entered into a Collaborative
Research and License Agreement (the "Bristol-Myers Squibb Agreement") pursuant
to which they agreed to collaborate to discover and develop novel antiinfective
drugs from leads obtained by screening six of Cubist's aminoacyl-tRNA synthetase
targets against Bristol-Myers Squibb's compound library. In connection with the
collaboration, Bristol-Myers Squibb has made a $4.0 million equity investment in
Cubist, has made $1.5 million in milestone payments and has made research
support payments to Cubist. See "Management's Discussion and Analysis of
Financial Condition and Results of Operations--Results of Operations." Under the
terms of the Bristol-Myers Squibb Agreement, Cubist is entitled to receive
additional research support payments and, if certain milestones are achieved,
additional milestone payments from Bristol-Myers Squibb. Cubist has granted to
Bristol-Myers Squibb an exclusive worldwide license to commercialize drugs
resulting from this collaboration. The development, manufacture and worldwide
sale of drugs resulting from the collaboration will be conducted by
Bristol-Myers Squibb, and Cubist will be entitled to receive royalties on the
worldwide sales of any drug developed and commercialized from this
collaboration.
 
    MERCK
 
    In June 1996, the Company and Merck entered into a Collaborative Research
and License Agreement (the "Merck Agreement") pursuant to which they agreed to
collaborate to discover and develop novel antiinfective drugs from leads
obtained by screening three of Cubist's aminoacyl-tRNA synthetase targets
against Merck's compound library. In connection with the collaboration, Merck
has made research support payments and has paid technology licensing fees to
Cubist. See "Management's Discussion and Analysis of Financial Condition and
Results of Operations--Results of Operations." Under the terms of the Merck
Agreement, Cubist is entitled to receive additional milestone payments from
Merck, if such milestones are achieved. Cubist has granted Merck an exclusive
worldwide license to commercialize drugs resulting from this collaboration. The
development, manufacture and worldwide sale of drugs resulting from the
collaboration will be conducted by Merck, and the Company will be entitled to
receive royalties on the worldwide sales of any drug developed and
commercialized from this collaboration.
 
    NOVARTIS
 
    In February 1999, the Company entered into a research and license agreement
with Novartis Pharma AG (the "Novartis Agreement") to use the Company's
proprietary VITA-TM- technology to validate and develop assays for antiinfective
targets and to identify new compounds for development as antiinfective
 
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agents. Both the Company's and Novartis' compound libraries will be screened
against these targets. In exchange for such license, Novartis will pay the
Company certain research payments and, if certain scientific and development
milestones are achieved, Novartis will make milestone payments. In addition,
Novartis will be required to pay royalties to the Company on worldwide sales of
any drug developed and commercialized from any products derived from this
collaboration. Upon the signing of the research and license agreement, Novartis
has made a $4.0 million equity investment in Cubist.
 
OTHER COLLABORATIONS
 
    To expand its access to novel small molecule libraries for screening and
target discovery, Cubist has formed and is currently engaged in alliances with
leading biotechnology companies including ArQule, Inc., Genzyme Corporation,
Neurogen Corporation and Helios Pharmaceuticals.
 
PATENTS AND PROPRIETARY TECHNOLOGY
 
    The Company seeks to protect its cloned targets, expressed proteins, assays,
organic synthetic processes, lead compounds, screening technology and certain
other technology by, among other things, filing, or causing to be filed on its
behalf, patent applications. Cubist has nine issued U.S. patents, twenty-six
pending U.S. patent applications and two pending international patent
applications. To date, the Company has received a notice of allowance for two of
these U.S. applications. Cubist has licensed, from the Massachusetts Institute
of Technology, three U.S. patents related to research technologies. There can be
no assurance that patents will be granted with respect to any of the Company's
pending patent applications or with respect to any patent applications filed by
the Company in the future.
 
    The commercial success of the Company will depend in part on not infringing
patents or proprietary rights of others. There can be no assurance that the
Company will be able to obtain a license to any third-party technology it may
require to conduct its business or that if obtainable, such technology can be
licensed at reasonable cost. Failure by the Company to obtain a license to
technology that it may require to utilize its technologies or commercialize its
products may have a material adverse effect on the Company's business, operating
results and financial condition. In some cases, litigation or other proceedings
may be necessary to defend against or assert claims of infringement, to enforce
patents issued to the Company, to protect trade secrets, know-how or other
intellectual property rights owned by the Company, or to determine the scope and
validity of the proprietary rights of third parties. Any potential litigation
could result in substantial costs to and diversion of resources by the Company
and could have a material adverse effect on the Company's business, operating
results and financial condition. There can be no assurance that any of the
Company's issued or licensed patents would ultimately be held valid or that
efforts to
 
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defend any of its patents, trade secrets, know-how or other intellectual
property rights would be successful. An adverse outcome in any such litigation
or proceeding could subject the Company to significant liabilities, require the
Company to cease using the subject technology or require the Company to license
the subject technology from the third party, all of which could have a material
adverse effect on the Company's business, operating results and financial
condition.
 
    Much of the know-how of importance to the Company's technology and many of
its processes are dependent upon the knowledge, experience and skills, which are
not patentable, of key scientific and technical personnel. To protect its rights
to and to maintain the confidentiality of trade secrets and proprietary
information, the Company requires employees, Scientific Advisory Board members,
consultants and collaborators to execute confidentiality and invention
assignment agreements upon commencement of a relationship with the Company.
These agreements prohibit the disclosure of confidential information to anyone
outside the Company and require disclosure and assignment to the Company of
ideas, developments, discoveries and inventions made by employees, advisors,
consultants and collaborators. There can be no assurance, however, that these
agreements will not be breached or that the Company's trade secrets or
proprietary information will not otherwise become known or developed
independently by others.
 
GOVERNMENT REGULATION
 
    OVERVIEW
 
    The development, manufacture and marketing of drugs (including antibiotics)
developed by the Company or its collaborative partners are subject to regulation
by numerous governmental agencies in the United States, principally the FDA, by
state and local governments, and in some instances by foreign governments.
Pursuant to the Federal Food, Drug, and Cosmetic Act and the regulations
promulgated thereunder (the "FDC Act"), the FDA regulates the pre-clinical and
clinical trials, safety, effectiveness, manufacture, labeling, storage,
distribution, and promotion of drugs. Product development and approval within
the FDA regulatory framework usually takes a significant number of years,
involves the expenditure of substantial capital resources and is uncertain.
 
                                       12
<PAGE>
    U.S. REGULATORY PROCESS
 
    Before testing in the United States of any compounds with potential
therapeutic value in human test subjects may begin, stringent government
requirements for preclinical data must be satisfied. Pre-clinical testing
includes both IN VITRO and IN VIVO laboratory evaluation and characterization of
the safety and efficacy of a drug and its formulation. Pre-clinical testing
results obtained from studies in several animal species, as well as from IN
VITRO studies, are submitted to the FDA as part of an IND and are reviewed by
the FDA prior to the commencement of human clinical trials. These pre-clinical
data must provide an adequate basis for evaluating both the safety and the
scientific rationale for the initial (Phase I) studies in human volunteers.
Unless the FDA objects to an IND, the IND becomes effective 30 days following
its receipt by the FDA. Once trials have commenced, the FDA may stop the trials
by placing them on "clinical hold" because of concerns about, for example, the
safety of the product being tested.
 
    Clinical trials involve the administration of the drug to healthy human
volunteers or to patients under the supervision of a qualified investigator,
usually a physician, pursuant to an FDA-reviewed protocol. Human clinical trials
are typically conducted in three sequential phases, although the phases may
overlap with one another. Clinical trials must be conducted under protocols that
detail the objectives of the study, the parameters to be used to monitor safety
and the efficacy criteria to be evaluated. Each protocol must be submitted to
the FDA as part of the IND.
 
    Phase I clinical trials represent the initial administration of the
investigational drug to a small group of healthy human subjects or, more rarely,
to a group of selected patients with the targeted disease or disorder. The goal
of Phase I clinical trials is typically to test for safety (adverse effects),
dose tolerance, absorption, biodistribution, metabolism, excretion and clinical
pharmacology and, if possible, to gain early evidence regarding efficacy.
 
    Phase II clinical trials involve a small sample of the actual intended
patient population and seek to assess the efficacy of the drug for specific
targeted indications, to determine dose tolerance and the optimal dose range and
to gather additional information relating to safety and potential adverse
effects.
 
    Once an investigational drug is found to have some efficacy and an
acceptable safety profile in the targeted patient population, Phase III clinical
trials are initiated to establish further clinical safety and efficacy of the
investigational drug in a broader sample of the general patient population at
geographically dispersed study sites in order to determine the overall
risk-benefit ratio of the drug and to provide an adequate basis for product
labeling. The Phase III clinical development program consists of expanded,
large-scale studies of patients with the target disease or disorder, to obtain
definitive statistical evidence of the efficacy and safety of the proposed
product and dosage regimen. All of the phases of clinical studies
 
                                       13
<PAGE>
must be conducted in conformance with the FDA's bioresearch monitoring
regulations.
 
    All data obtained from a comprehensive development program including
research and product development, manufacturing, pre-clinical and clinical
trials and related information are submitted in a new drug application ("NDA")
to the FDA and the corresponding agencies in other countries for review and
approval. In addition to reports of the trials conducted under the IND
application, the NDA includes information pertaining to the preparation of the
new drug or antibiotic, analytical methods, details of the manufacture of
finished products and proposed product packaging and labeling. Although the FDC
Act requires the FDA to review NDAs within 180 days of their filing, in practice
longer times may be required. The FDA also frequently requests that additional
information be submitted, requiring significant additional review time. Any
proposed product of the Company likely would be subject to demanding and
time-consuming NDA approval procedures in virtually all countries where
marketing of the products is intended. These regulations define not only the
form and content of safety and efficacy data regarding the proposed product but
also impose specific requirements regarding manufacture of the product, quality
assurance, packaging, storage, documentation and recordkeeping, labeling,
advertising and marketing procedures.
 
    The FDA has developed two "fast track" policies for certain new drugs, one
policy for expedited development and review, and one policy for accelerated
approval. The expedited review policy applies to new drug therapies, including
antibiotics, that are intended to treat persons with life-threatening and
severely-debilitating illnesses, especially where no satisfactory alternative
therapy exists. The FDA has defined "severely-debilitating" to mean diseases or
conditions that cause major irreversible morbidity. During the developmental
stage of drugs that qualify, the FDA expedites consultation and review of these
experimental therapies.
 
    The FDA's accelerated approval policy applies to certain new drug or
antibiotic products that have been studied for their safety and effectiveness in
treating serious or life-threatening illnesses and that provide "meaningful
therapeutic benefit to patients over existing treatments." This accelerated
approval, or fast track approach, is generally limited to new drugs or
antibiotics that treat patients that are unresponsive to, or intolerant of,
available therapy, or when there is improved patient response over currently
available therapy. The accelerated approval policy is further limited to drugs
for which the predictive value of the surrogate endpoint, in terms of clinical
outcome, has not been established. At the time of approval, the FDA may grant
approval on a surrogate endpoint or an effect on a clinical endpoint other than
survival or irreversible morbidity. The FDA may impose certain restrictions on
distribution, limiting its use to certain facilities or specialty-trained
physicians or making its use contingent on the performance of certain specified
medical procedures. Postmarketing studies (Phase IV trials) are usually
 
                                       14
<PAGE>
required to further affirm safety and/or efficacy. However, if an acceptable
clinical endpoint has been established, the drug must be evaluated for approval
under the traditional (non-fast track) approach.
 
    The Company is also subject to regulation under other federal laws and
regulation under state and local laws, including laws relating to occupational
safety, laboratory practices, the use, handling and disposition of radioactive
materials, environmental protection and hazardous substance control. Although
the Company believes that its safety procedures for handling and disposing of
radioactive compounds and other hazardous materials used in its research and
development activities comply with the standards prescribed by federal, state
and local regulations, the risk of accidental contamination or injury from these
materials cannot be completely eliminated. In the event of any such accident,
the Company could be held liable for any damages that result and any such
liability could exceed the resources of the Company.
 
COMPETITION
 
    The biotechnology and pharmaceutical industries are intensely competitive
and subject to rapid and significant technological change. Competitors of the
Company in the United States and elsewhere are numerous and include, among
others, major, multinational pharmaceutical and chemical companies, specialized
biotechnology firms and universities and other research institutions. Many of
these competitors employ greater financial and other resources, including larger
research and development staffs and more effective marketing and manufacturing
organizations, than the Company or its collaborative partners. Acquisitions of
competing companies and potential competitors by large pharmaceutical companies
or others could enhance financial, marketing and other resources available to
such competitors. As a result of academic and government institutions becoming
increasingly aware of the commercial value of their research findings, such
institutions are more likely to enter into exclusive licensing agreements with
commercial enterprises, including competitors of the Company, to market
commercial products. There can be no assurance that the Company's competitors
will not succeed in developing technologies and drugs that are more effective or
less costly than any which are being developed by the Company or which would
render the Company's technology and future drugs obsolete and noncompetitive.
 
    In addition, some of the Company's competitors have greater experience than
the Company in conducting pre-clinical and clinical trials and obtaining FDA and
other regulatory approvals. Accordingly, the Company's competitors may succeed
in obtaining FDA or other regulatory approvals for drug candidates more rapidly
than the Company. Companies that complete clinical trials, obtain required
regulatory agency approvals and commence commercial sale of their drugs before
their competitors may achieve a significant competitive advantage, including
certain patent and FDA marketing exclusivity rights that would delay the
Company's ability to market certain products. There can be no assurance that
drugs
 
                                       15
<PAGE>
resulting from the Company's research and development efforts, or from the joint
efforts of the Company and its collaborative partners, will be able to compete
successfully with competitors' existing products or products under development
or that they will obtain regulatory approval in the United States or elsewhere.
 
EMPLOYEES
 
    As of March 10, 1999, the Company had 54 full-time employees, 41 of whom
were engaged in research and development and 13 of whom were engaged in
management, administration and finance. Doctorates are held by 20 of the
Company's employees. The Company's employees are not covered by a collective
bargaining agreement. The Company has never experienced an employment-related
work stoppage and considers its employee relations to be good.
 
EXECUTIVE OFFICERS OF THE REGISTRANT
 
    The executive officers of the Company are as follows:
 
<TABLE>
<CAPTION>
NAME                                                       AGE                            POSITION
- -----------------------------------------------------      ---      -----------------------------------------------------
<S>                                                    <C>          <C>
Scott M. Rocklage, Ph.D..............................          44   President, Chief Executive Officer and Director
Francis P. Tally, M.D................................          58   Executive Vice President, Scientific Affairs
Thomas A. Shea.......................................          39   Vice President, Finance & Administration, and Chief
                                                                    Financial Officer, Treasurer
Dennis D. Keith, Ph.D................................          55   Vice President, Drug Discovery
Frederick B. Oleson, Jr., D.Sc.......................          49   Vice President, Drug Development
</TABLE>
 
    DR. ROCKLAGE has served as President and Chief Executive Officer and as a
member of the Board of Directors of the Company since July 1994. From 1990 to
1994, Dr. Rocklage served as President and Chief Executive Officer of Nycomed
Salutar, Inc., a diagnostic imaging company. From 1992 to 1994, he also served
as President and Chief Executive Officer and Chairman of Nycomed Interventional,
Inc., a medical device company. From 1986 to 1990, he served in various
positions at Nycomed Salutar, Inc., a diagnostic imaging company and was
responsible for designing and implementing research and development programs
that resulted in three drug products in human clinical trials, including the
approved drugs Omniscan and Teslascan. Dr. Rocklage received his B.S. in
Chemistry from the University of California, Berkeley and his Ph.D. in Chemistry
from the Massachusetts Institute of Technology.
 
    DR. TALLY has served as Executive Vice President, Scientific Affairs since
January 1997. From March 1995 to January 1997, he served the Company as Vice
President of Research and Development. From 1986 to 1995, Dr. Tally served as
Executive Director of Infectious Disease, Molecular Biology and
 
                                       16
<PAGE>
Natural Products Research at the Lederle Laboratories of American
Cyanamid/American Home Products, where he was responsible for worldwide clinical
studies for piperacillin/tazobactam which was registered for sales in Europe in
1992, approved by the FDA in 1993 and marketed as Zosyn. From 1975 to 1986, he
served as Senior Physician in Infectious Disease at the New England Medical
Center and Associate Professor of Medicine at Tufts Medical Center. Dr. Tally
received his A.B. in Biology from Providence College and his M.D. from George
Washington University School of Medicine.
 
    DR. KEITH has served as Vice President, Drug Discovery since October 1997.
Dr. Keith joined Cubist from Hoffman-La Roche Inc. where he served in various
positions from 1971-1997, the most recent of which was Director of Antiinfective
Chemistry. Dr. Keith received his B.S. in Chemistry from Bates College and his
Ph.D. in Organic Chemistry from Yale University.
 
    DR. OLESON has served as Vice President, Drug Development since November
1997. Prior to joining Cubist, Dr. Oleson served as an independent consultant
from June 1997 to November 1997; Director of Preclinical Research at AutoImmune,
Inc., a biotechnology company, from January 1997 to June 1997; Director,
Toxicology and Preclinical Pharmacology at Biogen, Inc., a biotechnology
company, from 1992 to 1997 and in various positions at Bristol-Myers Squibb from
1983 to 1992. Dr. Oleson was a key contributor in the development of the Biogen
drug Avonex and a key consultant in the development of Hirulog for The Medicines
Company. Dr. Oleson received his B.S. in Biochemistry from Princeton University
and a Doctor of Science in Physiology/Radiation Biology from Harvard University
School of Public Health.
 
    MR. SHEA has served as Vice President, Finance and Administration and Chief
Financial Officer since December 1998. He has served as Treasurer and Chief
Accounting Officer since June 1996. From December 1997 to December 1998 he
served as Senior Director of Finance and Administration. Previous to that he was
Director of Finance and Administration. From 1987 to 1993, he served as Manager
of Accounting/MIS and Budget and Financial Analyst at ImmuLogic Pharmaceutical
Corporation, a biotechnology company. Mr. Shea received his B.S. in
Accounting/Law from Babson College and his Masters in Business Administration
from Suffolk University.
 
RISK FACTORS
 
    STOCKHOLDERS AND PROSPECTIVE PURCHASERS OF THE COMPANY'S COMMON STOCK SHOULD
CAREFULLY CONSIDER THE FOLLOWING RISK FACTORS, IN ADDITION TO THE OTHER
INFORMATION APPEARING IN THIS ANNUAL REPORT ON FORM 10-K.
 
    EARLY STAGE OF PRODUCT DEVELOPMENT; NO ASSURANCE OF SUCCESSFUL
COMMERCIALIZATION. Since inception, the Company has generated no revenue from
product sales. The Company's research and development programs are at an early
stage, and the Company does not expect that any drugs resulting from its
research
 
                                       17
<PAGE>
and development efforts, or from the joint efforts of the Company and its
collaborative partners, will be commercially available for a significant number
of years, if at all. The Company has one drug candidate in clinical development.
To date, the Company has not, independently or with its collaborative partners,
completed the optimization of any lead candidates. Any drug candidates developed
by the Company will require significant additional research and development
efforts, including extensive preclinical (animal and IN VITRO data) and clinical
testing and regulatory approval, prior to commercial sale. Only one of the
Company's drug candidates has advanced to any phase of preclinical or clinical
trials. There can be no assurance that the Company's approach to drug discovery,
acting independently or with the efforts of any collaborative partner of the
Company, will be effective or will result in the development of any drug. The
Company's drug candidates will be subject to the risks of failure inherent in
the development of pharmaceutical products based on new technologies. These
risks include the possibilities that any or all of the Company's drug candidates
will be found to be unsafe, ineffective or toxic or otherwise fail to meet
applicable regulatory standards or receive necessary regulatory clearances; that
these drug candidates, if safe and effective, will be difficult to develop into
commercially viable drugs or to manufacture on a large scale or will be
uneconomical to market; that proprietary rights of third parties will preclude
the Company from marketing such drugs; or that third parties will market
superior or equivalent drugs. The failure to develop safe, commercially viable
drugs would have a material adverse effect on the Company's business, operating
results and financial condition.
 
    UNCERTAINTY DUE TO UNPROVEN TECHNOLOGY.  The Company's drug discovery
approach faces technical issues which have not been resolved and requires the
development of multiple novel technologies to create a successful drug
candidate. While the Company has demonstrated that certain compounds have the
ability to inhibit the activity of certain molecular targets, the Company has
not proven that this activity can be utilized clinically as a therapeutic.
Furthermore, there can be no assurance that the inhibitory activity already
demonstrated in primary screening will continue to be encouraging in further
screening or drug discovery studies. The Company has not tested any drug
candidates developed from the Company's drug discovery program in humans, and
there can be no assurance that there will be clinical benefits associated with
any such drug candidates. Furthermore, there can be no assurance that the
Company will successfully address these technological challenges or others that
may arise in the course of development. Any failure of the Company to anticipate
or respond adequately to technological developments will have a material adverse
effect on the Company's business, operating results and financial condition.
There can be no assurance that the Company will be able to employ its drug
discovery approach successfully.
 
                                       18
<PAGE>
    DEPENDENCE ON COLLABORATIVE PARTNERS AND OTHERS. A key element of the
Company's strategy is to enhance certain of its drug discovery and development
programs and to fund its capital requirements, in part, by entering into
collaborative agreements with major pharmaceutical companies. The Company is a
party to collaborative agreements with Novartis, Bristol-Myers Squibb and Merck
(collectively, the "Collaborative Agreements"). Under the Collaborative
Agreements, each of Novartis, Bristol-Myers Squibb and Merck is responsible for
(i) providing libraries of compounds for screening against certain of the
Company's targets, (ii) selecting compounds determined to be leads in the
screening for subsequent development, (iii) conducting preclinical and clinical
trials and obtaining required regulatory approvals of drug candidates, and (iv)
manufacturing and commercializing resulting drugs. As a result, the Company's
receipt of revenues (whether in the form of continued research funding, drug
development milestones or royalties on sales) under the Collaborative Agreements
is dependent upon the decisions made by the manufacturing and marketing
resources of its collaborative partners. The Company's collaborative partners
are not obligated to develop or commercialize any drug candidates resulting from
the Collaborative Agreements. The amount and timing of resources dedicated by
the Company's collaborative partners to their respective collaborations with the
Company are not within the Company's control. Moreover, certain drug candidates
discovered by the Company may be viewed by the Company's collaborative partners
as competitive with such partners' drugs or drug candidates. Accordingly, there
can be no assurance that the Company's collaborative partners will elect to
proceed with the development of drug candidates which the Company believes to be
promising or that they will not pursue their existing or alternative
technologies in preference to such drug candidates. There can be no assurance
that the interests of the Company will continue to coincide with those of its
collaborative partners, that some of the Company's collaborative partners will
not develop independently, or with third parties, drugs that could compete with
drugs of the types contemplated by the Collaborative Agreements, or that
disagreements over rights or technology or other proprietary interests will not
occur.
 
    If any of the Company's collaborative partners breaches or terminates its
agreement with the Company, or otherwise fails to conduct its collaborative
activities in a timely manner, the development or commercialization of any drug
candidate or research program under these Collaborative Agreements may be
delayed, the Company may be required to undertake unforeseen additional
responsibilities or to devote unforeseen additional resources to such
development or commercialization, or such development or commercialization could
be terminated. Any such event could materially adversely affect the Company's
financial condition, intellectual property position and operations. In addition,
there have been a significant number of recent consolidations among
pharmaceutical companies. Such consolidations among the companies with which the
Company is collaborating could result in the diminution or termination of, or
 
                                       19
<PAGE>
delays in, the development or commercialization of drug candidates or research
programs under one or more of the Collaborative Agreements.
 
    ADDITIONAL FINANCING REQUIREMENTS; UNCERTAINTY OF AVAILABLE FUNDING.  The
Company will require substantial additional funds for its drug discovery and
development programs, for operating expenses, for clinical trials, for pursuing
regulatory clearances, for the development of manufacturing, marketing and sales
capabilities and for prosecuting and defending its intellectual property rights
before it can expect to realize significant revenues from commercial sales. The
Company intends to seek such additional funding through public or private
financing or collaborative or other arrangements with corporate partners. If
additional funds are raised by issuing equity securities, further dilution to
existing stockholders may result and future investors may be granted rights
superior to those of existing stockholders. There can be no assurance, however,
that additional financing will be available from any of these sources or, if
available, will be available on acceptable or affordable terms. If adequate
funds are not available, the Company may be required to delay, reduce the scope
of or eliminate one or more of its research and development programs or to
obtain funds by entering into arrangements with collaborative partners or others
that require the Company to issue additional equity securities or to relinquish
rights to certain technologies or drug candidates that the Company would not
otherwise issue or relinquish in order to continue independent operations. See
"Management's Discussion and Analysis of Financial Condition and Results of
Operations."
 
    HISTORY OF LOSSES AND EXPECTATION OF FUTURE LOSSES; UNCERTAINTY OF FUTURE
PROFITABILITY. The Company has incurred a cumulative operating loss of
approximately $34.8 million through December 31, 1998. Losses have resulted
principally from costs incurred in research and development activities related
to the Company's efforts to develop daptomycin, to develop target assays,
acquisition and chemical optimization of compounds, automated high throughput
screening and from the associated administrative costs. The Company expects to
incur significant additional operating losses over the next several years and
expects cumulative losses to increase substantially due to expanded research and
development efforts, preclinical and clinical trials and development of
manufacturing, marketing and sales capabilities. In the next few years, the
Company's revenues may be limited to research support payments under the
Collaborative Agreements and any amounts received under other research or drug
development collaborations that the Company has established or will establish.
There can be no assurance, however, that the Company will be able to establish
any additional collaborative relationships on terms acceptable to the Company or
maintain in effect the current Collaborative Agreements. The Company's ability
to achieve significant revenue or profitability is dependent on its or its
collaborative partners' ability to successfully complete the development of drug
candidates, to develop and obtain patent protection and regulatory approvals for
the drug candidates and to manufacture and commercialize the resulting drugs.
The Company will not receive
 
                                       20
<PAGE>
revenues or royalties from commercial sales for a significant number of years,
if at all. Failure to receive significant revenues or achieve profitable
operations would impair the Company's ability to sustain operations. There can
be no assurance that the Company will ever successfully develop, commercialize,
patent, manufacture and market any products, obtain required regulatory
approvals or achieve profitability. See "Management's Discussion and Analysis of
Financial Condition and Results of Operations."
 
    UNCERTAINTY OF PATENTS AND PROPRIETARY RIGHTS.  The Company's success will
depend in part on its ability to obtain U.S. and foreign patent protection for
its drug candidates and processes, preserve its trade secrets and operate
without infringing the proprietary rights of third parties. Because of the
length of time and expense associated with bringing new drug candidates through
the development and regulatory approval process to the marketplace, the
pharmaceutical industry has traditionally placed considerable importance on
obtaining patent and trade secret protection for significant new technologies,
products and processes. There can be no assurance that any additional patents
will issue from any of the patent applications owned by, or licensed to, the
Company. Further, there can be no assurance that any rights the Company may have
under issued patents will provide the Company with significant protection
against competitive products or otherwise be commercially viable. Legal
standards relating to the validity of patents covering pharmaceutical and
biotechnological inventions and the scope of claims made under such patents are
still developing. There is no consistent policy regarding the breadth of claims
allowed in biotechnology patents. The patent position of a biotechnology firm is
highly uncertain and involves complex legal and factual questions. There can be
no assurance that any existing or future patents issued to, or licensed by, the
Company will not subsequently be challenged, infringed upon, invalidated or
circumvented by others. In addition, patents may have been granted, or may be
granted, covering products or processes that are necessary or useful to the
development of the Company's drug candidates. If the Company's drug candidates
or processes are found to infringe upon the patents, or otherwise impermissibly
utilize the intellectual property of others, the Company's development,
manufacture and sale of such drug candidates could be severely restricted or
prohibited. In such event, the Company may be required to obtain licenses from
third parties to utilize the patents or proprietary rights of others. There can
be no assurance that the Company will be able to obtain such licenses on
acceptable terms, or at all. There has been significant litigation in the
industry regarding patents and other proprietary rights. If the Company becomes
involved in litigation regarding its intellectual property rights or the
intellectual property rights of others, the potential cost of such litigation
and the potential damages that the Company could be required to pay could be
substantial.
 
    In addition to patent protection, the Company relies on trade secrets,
proprietary know-how and technological advances which it seeks to protect, in
part, by confidentiality agreements with its collaborative partners, employees
and consultants. There can be no assurance that these confidentiality agreements
 
                                       21
<PAGE>
will not be breached, that the Company would have adequate remedies for any such
breach, or that the Company's trade secrets, proprietary know-how and
technological advances will not otherwise become known or be independently
discovered by others.
 
    UNCERTAINTY ASSOCIATED WITH PRECLINICAL AND CLINICAL TESTING.  Before
obtaining regulatory approvals for the commercial sale of any of the Company's
potential drugs, the drug candidates will be subject to extensive preclinical
and clinical trials to demonstrate their safety and efficacy in humans. The
Company is dependent on its collaborative partners to conduct clinical trials
for the drug candidates resulting from the Collaborative Agreements and may
become dependent on other third parties to conduct future clinical trials of its
internally developed drug candidates. The Company has no experience in
conducting preclinical or clinical trials, and preclinical or clinical trials
have been commenced with respect to only one of the Company's drug candidates
and none of the drug candidates being developed jointly by the Company and its
collaborative partners. Furthermore, there can be no assurance that preclinical
or clinical trials of any drug candidates will demonstrate the safety and
efficacy of such drug candidates at all or to the extent necessary to obtain
regulatory approvals. Companies in the biotechnology industry have suffered
significant setbacks in advanced clinical trials, even after demonstrating
promising results in earlier trials. The failure to adequately demonstrate the
safety and efficacy of a drug candidate under development could delay or prevent
regulatory approval of the drug candidate and would have a material adverse
effect on the Company's business, operating results and financial condition.
 
    NO ASSURANCE OF MARKET ACCEPTANCE.  There can be no assurance that any drugs
successfully developed by the Company, independently or with its collaborative
partners, if approved for marketing, will achieve market acceptance. The
antiinfective drugs which the Company is attempting to develop will compete with
a number of well-established antiinfective drugs manufactured and marketed by
major pharmaceutical companies. The degree of market acceptance of any drugs
developed by the Company will depend on a number of factors, including the
establishment and demonstration of the clinical efficacy and safety of the
Company's drug candidates, their potential advantage over existing therapies and
reimbursement policies of government and third-party payers. There is no
assurance that physicians, patients or the medical community in general will
accept and utilize any drugs that may be developed by the Company independently
or with its collaborative partners.
 
    INTENSE COMPETITION.  The biotechnology and pharmaceutical industries are
intensely competitive and subject to rapid and significant technological change.
Competitors of the Company in the United States and elsewhere are numerous and
include, among others, major multinational pharmaceutical and chemical
companies, specialized biotechnology firms and universities and other research
institutions. Many of these competitors employ greater financial and other
resources, including larger research and development staffs
 
                                       22
<PAGE>
and more effective marketing and manufacturing organizations, than the Company
or its collaborative partners. Acquisitions of competing companies and potential
competitors by large pharmaceutical companies or others could enhance financial,
marketing and other resources available to such competitors. As a result of
academic and government institutions becoming increasingly aware of the
commercial value of their research findings, such institutions are more likely
to enter into exclusive licensing agreements with commercial enterprises,
including competitors of the Company, to market commercial products. There can
be no assurance that the Company's competitors will not succeed in developing
technologies and drugs that are more effective or less costly than any which are
being developed by the Company or which would render the Company's technology
and future drugs obsolete and noncompetitive.
 
    In addition, some of the Company's competitors have greater experience than
the Company in conducting preclinical and clinical trials and obtaining U.S. FDA
and other regulatory approvals. Accordingly, the Company's competitors may
succeed in obtaining FDA or other regulatory approvals for drug candidates more
rapidly than the Company. Companies that complete clinical trails, obtain
required regulatory agency approvals and commence commercial sale of their drugs
before their competitors may achieve a significant competitive advantage,
including certain patent and FDA marketing exclusivity rights that would delay
the Company's ability to market certain products. There can be no assurance that
drugs resulting from the Company's research and development efforts, or from the
joint efforts of the Company and its collaborative partners, will be able to
compete successfully with competitors' existing products or products under
development or that they will obtain regulatory approval in the United States or
elsewhere.
 
    IMPACT OF EXTENSIVE GOVERNMENT REGULATION.  The FDA and comparable agencies
in foreign countries impose substantial requirements upon the introduction of
pharmaceutical products through lengthy and detailed preclinical, laboratory and
clinical testing procedures, sampling activities and other costly and
time-consuming procedures to establish their safety and efficacy. All of the
Company's drug candidates will require governmental approvals for
commercialization, none of which have been obtained. Preclinical and clinical
trials and manufacturing of the Company's drug candidates will be subject to the
rigorous testing and approval processes of the FDA and corresponding foreign
regulatory authorities. Satisfaction of these requirements typically take a
significant number of years and can vary substantially based upon the type,
complexity and novelty of the product. To date, the Company has filed an IND
with the FDA in connection with daptomycin. There can be no assurance as to when
the Company, independently or with its collaborative partners, might submit an
additional IND for FDA or other regulatory review. Government regulation also
affects the manufacturing and marketing of pharmaceutical products.
 
    The effect of government regulation may be to delay marketing of the
Company's potential drugs for a considerable or indefinite period of time,
impose costly procedural requirements upon the Company's
 
                                       23
<PAGE>
activities and furnish a competitive advantage to larger companies or companies
more experienced in regulatory affairs. Delays in obtaining governmental
regulatory approval could adversely affect the Company's marketing as well as
the Company's ability to generate significant revenues from commercial sales.
There can be no assurance that FDA or other regulatory approvals for any drug
candidates developed by the Company will be granted on a timely basis or at all.
Moreover, if regulatory approval of a drug candidate is granted, such approval
may impose limitations on the indicated use for which such drug may be marketed.
Even if initial regulatory approvals for the Company's drug candidates are
obtained, the Company, its drugs and its manufacturing facilities would be
subject to continual review and periodic inspection, and later discovery of
previously unknown problems with a drug, manufacturer or facility may result in
restrictions on such drug or manufacturer, including withdrawal of the drug from
the market. The regulatory standards are applied stringently by the FDA and
other regulatory authorities and failure to comply can, among other things,
result in fines, denial or withdrawal of regulatory approvals, product recalls
or seizures, operating restrictions and criminal prosecution.
 
    As more fully described in "Government Regulation" herein, the FDA has
developed two "fast track" policies for certain new drugs (including
antibiotics), one policy for expedited development and review and one policy for
accelerated approval. The expedited development and review policy applies to new
drug therapies that are intended to treat persons with life-threatening and
severely debilitating illnesses, especially where no satisfactory alternative
therapy exists. There can be no assurance that any drug candidate contemplated
by the Company will qualify for the FDA's various fast track or priority
approval policies. Nor can there be any assurance that such policies will remain
as currently implemented by the FDA. As with many biotechnology and
pharmaceutical companies, the Company is subject to numerous environmental and
safety laws and regulations. Any violation of, and the cost of compliance with,
these regulations could materially adversely affect the Company's business,
operating results and financial condition. The Company is subject to periodic
inspections and has not received notice of any material violations of any
environmental or safety law or regulation.
 
    DEPENDENCE ON KEY PERSONNEL.  The Company is highly dependent upon the
efforts of its senior management and scientific team, including its President
and Chief Executive Officer. Although Dr. Rocklage has entered into an
employment agreement with the Company, the terms of the employment agreement
provide that Dr. Rocklage may terminate his employment with the Company at any
time upon thirty days' written notice. None of the Company's other executive
officers or key employees has entered into an employment agreement with the
Company. The loss of the services of one or more of these individuals might
impede the achievement of the Company's development objectives. Because of the
specialized scientific nature of the Company's business, the Company is highly
dependent upon its ability to attract and retain qualified scientific and
technical personnel. There is intense competition among major
 
                                       24
<PAGE>
pharmaceutical and chemical companies, specialized biotechnology firms and
universities and other research institutions for qualified personnel in the
areas of the Company's activities. There can be no assurance that the Company
will be able to continue to attract and retain the qualified personnel necessary
for the development of its business. Loss of the services of, or failure to
recruit, key scientific and technical personnel could adversely affect the
Company's business, operating results and financial condition.
 
    DEPENDENCE OF KEY PRODUCT.  The Company is highly dependent upon its lead
in-licensed product daptomycin. Although Phase III clinical trials have begun
with respect to the intravenous formulation of daptomycin, there can be no
assurance that it will achieve FDA approval or, if approved, that daptomycin
will be successfully marketed, distributed or utilized. Unless other products
are developed or in-licensed, the failure of daptomycin could adversely affect
the Company's business, operating results and financial condition. There can be
no assurance that other products will be developed or in-licensed by the
Company.
 
    LACK OF MANUFACTURING, MARKETING AND SALES CAPABILITY AND
EXPERIENCE.  Cubist has not yet made any significant investment in the
development of marketing or sales capabilities and has made only a modest
investment in manufacturing capabilities through an outside source. The Company
has no experience in manufacturing of products in accordance with Good
Manufacturing Practices as prescribed by the FDA or to produce an adequate
supply of compounds to meet future requirements for clinical trials. If the
Company is unable to develop or contract for manufacturing capabilities on
acceptable terms, the Company's ability to conduct preclinical and clinical
trials with the Company's drug candidates will be adversely affected, resulting
in delays in the submission of drug candidates for regulatory approvals and in
the initiation of new development programs, which in turn could materially
impair Cubist's competitive position and the possibility of achieving
profitability.
 
    The Company has no experience in marketing drugs. The Company has granted
marketing rights to its collaborative partners with respect to drugs developed
through the Collaborative Agreements. The Company may seek to collaborate with a
third party to market those drugs for which it has retained or licensed
marketing rights or may seek to market and sell such drugs directly. If the
Company seeks to collaborate with a third party, there can be no assurance that
a collaborative agreement can be reached on acceptable terms. If the Company
seeks to market and sell such drugs directly, the Company will need to hire
additional personnel skilled in marketing and sales as it develops drugs with
commercial potential. There can be no assurance that the Company will be able to
acquire, or establish third-party relationships to provide, any or all of these
capabilities.
 
    REIMBURSEMENT AND DRUG PRICING UNCERTAINTY The successful commercialization
of, and the interest of potential collaborative partners to invest in, the
development of the Company's drug candidates will depend substantially on
reimbursement of the costs of the resulting drugs and related treatments at
 
                                       25
<PAGE>
acceptable levels from government authorities, private health insurers and other
organizations, such as health maintenance organizations ("HMOs"). There can be
no assurance that reimbursement in the United States or elsewhere will be
available for any drugs the Company may develop or, if available, will not be
decreased in the future, or that reimbursement amounts will not reduce the
demand for, or the price of, the Company's drugs, thereby adversely affecting
the Company's business. If reimbursement is not available or is available only
to limited levels, there can be no assurance that the Company will be able to
obtain collaborative partners to manufacture and commercialize drugs, or would
be able to obtain a sufficient financial return on its own manufacture and
commercialization of any future drugs.
 
    Third-party payers are increasingly challenging the prices charged for
medical products and services. Also, the trend toward managed health care in the
United States and the concurrent growth of organizations such as HMOs, which can
control or significantly influence the purchase of health care services and
products, as well as legislative proposals to reform health care or reduce
government insurance programs, may result in lower prices for pharmaceutical
products. The cost containment measures that health care providers are
instituting, including practice protocols and guidelines and clinical pathways,
and the effect of any health care reform, could materially adversely affect the
Company's ability to sell any of its drugs if successfully developed and
approved. Moreover, the Company is unable to predict what additional legislation
or regulation, if any, relating to the health care industry or third-party
coverage and reimbursement may be enacted in the future or what effect such
legislation or regulation would have on the Company's business.
 
    POTENTIAL PRODUCT LIABILITY AND AVAILABILITY OF INSURANCE.  The Company's
business exposes it to potential liability risks that are inherent in the
testing, manufacturing and marketing of pharmaceutical products. The use of the
Company's drug candidates in clinical trials may expose the Company to product
liability claims and possible adverse publicity. These risks will expand with
respect to the Company's drug candidates, if any, that receive regulatory
approval for commercial sale. Product liability insurance for the biotechnology
industry is generally expensive, if available at all. The Company does have
product liability insurance for its one product in clinical trials, however,
such coverage is becoming increasingly expensive and there can be no assurance
that the Company will be able to obtain insurance coverage at acceptable costs
or in a sufficient amount, in the future, or that a product liability claim
would not adversely affect the Company's business, operating results or
financial condition.
 
ITEM 2. DESCRIPTION OF PROPERTY
 
    The Company's headquarters and research and development facilities are
located in a 24,000 square foot facility leased by the Company in Cambridge,
Massachusetts at 24 Emily Street. The Company
 
                                       26
<PAGE>
believes that this space will be adequate for its research and drug development
activities for at least the next year.
 
ITEM 3. LEGAL PROCEEDINGS
 
    The Company is not a party to any material legal proceedings.
 
ITEM 4. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS
 
    No matters were submitted to a vote of security holders during the last
quarter of the fiscal year ended December 31, 1998.
 
                                       27
<PAGE>
                                    PART II
 
ITEM 5. MARKET FOR REGISTRANTS' COMMON EQUITY AND RELATED STOCKHOLDER MATTERS
 
MARKET INFORMATION
 
    The Company's common stock is traded on the Nasdaq National Market under the
symbol "CBST". The following table sets forth, for the period indicated, the
high and low sale prices per share of the Company's common stock as reported by
the Nasdaq National Market.
 
<TABLE>
<CAPTION>
1997                                                                            HIGH        LOW
- ----------------------------------------------------------------------------  ---------  ---------
<S>                                                                           <C>        <C>
First Quarter...............................................................  $   13.00  $    6.00
Second Quarter..............................................................  $   10.25  $    6.00
Third Quarter...............................................................  $    7.50  $    5.00
Fourth Quarter..............................................................  $    8.25  $    4.88
 
1998
First Quarter...............................................................  $    5.75  $    4.25
Second Quarter..............................................................  $    5.69  $    4.50
Third Quarter...............................................................  $    4.69  $    2.03
Fourth Quarter..............................................................  $    3.81  $    2.00
</TABLE>
 
HOLDERS
 
    As of March 5, 1999, the Company had approximately 154 stockholders of
record. This does not reflect persons or entitles who hold their stock in
nominee or "street" name through various brokerage firms.
 
DIVIDENDS
 
    The Company has not declared or paid any cash dividends on its Common Stock
since its inception and does not anticipate paying cash dividends in the
foreseeable future.
 
                                       28
<PAGE>
RECENT SALES OF UNREGISTERED SECURITIES
 
    Described below is information regarding all securities of the Company sold
by the Company during the fiscal year ended December 31, 1998, which, unless
otherwise noted below, were not registered under the Securities Act of 1933, as
amended (the "Securities Act").
 
    In September 1998, the Company issued and sold an aggregate of 6,065,560
shares of Common Stock at a purchase price of $2.25 per share and issued
warrants exercisable for 3,032,783 shares of Common Stock. Such warrants are
exercisable over a five year period at an exercise price of $2.25 per share. The
issuance and sale of such shares of Common Stock were made in reliance on Rule
506 of Regulation D promulgated under Section 4(2) of the Securities Act. These
shares were subsequently registered with the Securities and Exchange Commission.
 
    The Company's Registration Statement on Form S-1 (Reg. No. 333-6795) in
connection with the Company's initial public offering of Common Stock was
declared effective by the Securities and Exchange Commission ("the SEC") on
October 25, 1996.   On October 25, 1996, the Company also filed another
Registration Statement on Form S-1 (Reg. No. 333-5880) with the SEC pursuant to
Rule 462 (b) promulgated under the Securities Act of 1933, as amended (the
"Securities Act"). Such Registration Statements (together the "IPO Registration
Statement") provided for the registration under the Securities Act of 2,875,000
shares of the Company's Common Stock.
 
    The aggregate initial public offering proceeds for all 2,875,000 shares of
Common Stock registered under the Securities Act pursuant to the IPO
Registration Statement was $17,250,000. The net proceeds to the Company from
such issuance and distribution, after deducting the aggregate amount of expenses
(including underwriting discounts and commissions) paid by the Company in
connection therewith, were $15,153,000.
 
    Of such net proceeds, an aggregate of $9,124,000 has been spent through
December 31, 1998 for the following uses and in the following amounts per use:
$342,000 in construction of plant, building and facilities; $1,803,000 for
repayment of indebtedness; $6,979,000 for working capital. All amounts spent by
the Company for such uses, other than payment of salaries to directors and
officers of the Company, consisted of direct payments to persons or entities,
none of which was a director or officer of the Company, holder of 10 percent or
more of any class of equity securities of the Company or other affiliate of the
Company. The remaining balance of such net proceeds, consisting of $6,029,000,
are held in cash, cash equivalents, and investments.
 
                                       29
<PAGE>
ITEM. 6. SELECTED FINANCIAL DATA
 
<TABLE>
<CAPTION>
                                                                                YEARS ENDED DECEMBER 31,
                                                                          (IN THOUSANDS, EXCEPT PER SHARE DATA)
                                                                  -----------------------------------------------------
<S>                                                               <C>        <C>        <C>        <C>        <C>
                                                                    1998       1997       1996       1995       1994
                                                                  ---------  ---------  ---------  ---------  ---------
STATEMENT OF OPERATIONS DATA:
Total revenues..................................................  $   1,634  $   2,733  $   4,985  $   1,271  $      --
Research and development expenses...............................     10,489      9,341      6,871      4,965      3,309
General and administrative expenses.............................      3,495      3,292      1,989      1,708      1,449
Other income (1)................................................         --      1,833         --         --         --
Net loss........................................................    (11,825)    (7,265)    (3,799)    (5,396)    (4,813)
Basic and diluted net loss per share............................  $   (0.97) $   (0.73) $   (1.49) $   (5.47) $   (7.61)
Weighted average number of common shares outstanding............     12,224      9,995      2,554        986        633
</TABLE>
 
- ------------------------
 
(1) Gain on the sale of the Company's equity position in Novalon.
 
<TABLE>
<CAPTION>
                                                                              YEARS ENDED DECEMBER 31,
                                                                                   (IN THOUSANDS)
                                                                -----------------------------------------------------
<S>                                                             <C>        <C>        <C>        <C>        <C>
                                                                  1998       1997       1996       1995       1994
                                                                ---------  ---------  ---------  ---------  ---------
BALANCE SHEET DATA:
Cash and cash equivalents and short and long-term
  investments.................................................  $  19,012  $  18,116  $  19,329  $   3,056  $   1,221
Total assets..................................................     23,137     21,673     23,452      7,048      4,250
Long-term obligations.........................................      1,308      1,105      1,053      1,257      2,032
Stockholder's equity..........................................     20,086     19,063     20,299      4,895        823
Dividends.....................................................         --         --         --         --         --
</TABLE>
 
ITEM. 7 MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS
 
OVERVIEW
 
    Since its incorporation on May 1, 1992 and commencement of operations in
February 1993, Cubist has been engaged in the research, development and
commercialization of novel antiinfective drugs to treat
 
                                       30
<PAGE>
infectious diseases caused by bacteria and fungi. The Company has a limited
history of operations and has experienced significant operating losses since
inception. The Company expects to incur significant additional operating losses
over the next several years and expects cumulative losses to increase
substantially due to expanded research and development efforts, pre-clinical and
clinical trials and development of manufacturing, marketing and sales
capabilities.
 
    A key element of the Company's strategy is to enhance certain of its drug
discovery and development programs and to fund its capital requirements, in
part, by entering into collaborative agreements with major pharmaceutical
companies. The Company is a party to collaborative agreements based specifically
on its aminoacyl-tRNA synthetase program with Bristol-Myers Squibb and Merck.
Under these collaborative agreements, the Company is entitled to receive
research support payments and, if certain drug development milestones are
achieved, milestone payments. In addition, the Company will be entitled to
receive royalties on worldwide sales of any drug developed and commercialized
from these collaborations.
 
    On February 3, 1999, the Company entered into a research and license
agreement with Novartis Pharma AG ("Novartis") to use the Company's proprietary
VITA-TM- technology to validate and develop assays for antiinfective targets and
to identify new compounds for development as antiinfective agents. In exchange
for such license, Novartis will pay the Company certain research payments and if
certain scientific and development milestones are achieved, Novartis will make
milestone payments. In addition, Novartis will be required to pay royalties to
the Company on worldwide sales of any drug developed and commercialized from any
products derived from this collaboration. Upon the signing of the research and
license agreement, Novartis purchased, and the Company issued to Novartis,
797,488 shares of Common Stock for a total purchase price of $4.0 million in
cash. The proceeds from the sale of these shares will be primarily used to fund
the clinical development of daptomycin and development of the VITA-TM-
technology.
 
    On September 23, 1998, the Company completed a private placement financing
with investors and raised approximately $12.7 million (net of financing costs of
$901,000) by issuing 6,065,560 shares at $2.25 per share, along with warrants
exercisable for 3,032,783 shares of Common Stock at $2.25 per share. The Company
has filed an S-3 registration statement to register the resale of the 9,098,343
shares of Common Stock related to this financing. The proceeds of this private
offering will be used primarily to fund the clinical development of daptomycin
and the development of its proprietary genomic target validation and assay
development (VITA-TM-) technology. These additional funds together with existing
cash resources are expected to be used to fund the Company's operations and
capital requirements through 1999.
 
    On November 7, 1997, the Company entered into a license agreement with Eli
Lilly and Company ("Eli Lilly") pursuant to which the Company acquired exclusive
worldwide rights to develop, manufacture and market daptomycin. In exchange for
such license, the Company has paid to Eli Lilly an upfront license
 
                                       31
<PAGE>
fee in cash, and if certain drug development milestones are achieved, has agreed
to pay milestone payments in cash or by issuing shares of Common Stock to Eli
Lilly. In addition, the Company will be required to pay royalties to Eli Lilly
on worldwide sales of daptomycin. Daptomycin is a novel, natural product being
developed for the treatment of STAPHYLOCOCCUS AUREUS and enterococcus infections
in humans. The Company began clinical trials of daptomycin in February of 1999.
 
YEAR 2000 READINESS
 
    The "Year 2000" issue generally describes the various problems which may
result from the improper processing of dates and date-sensitive calculations.
Computers and other equipment containing computer-related components (such as
programmable logic controllers and other embedded systems) using two digits to
identify the year in a date may not be able to distinguish between dates in the
20th century versus the 21st century. Because computer and microprocessor use is
so widespread, the issue has become a societal concern, the impact of which is
not yet known.
 
    The Company has completed the assessment of its critical computer systems
and embedded systems and believes them to be Year 2000 compliant. Although the
Company believes its critical systems are Year 2000 compliant, there can be no
assurances that other defects will not be discovered in the future. The Company
believes that any failure of the Company's non-critical systems to be Year 2000
compliant will not have a material adverse effect on the Company.
 
    In addition to the Company's critical systems, the Company relies on third
party service providers and suppliers (i.e., payroll services company,
telecommunications companies, banks and utility companies and contract
manufacturers) in the conduct of its business, and it recognizes that there may
be potential exposure to Year 2000-related business disruptions as a result. The
Company has contacted its significant service providers and contract
manufacturers and has obtained assurances from some that they are addressing
Year 2000 issues in a prudent fashion. Others have not replied in any fashion,
but none have informed the Company of material Year 2000 issues. The Company is
unable to control whether the firms and suppliers it does business with
currently, and in the future, will have systems which are Year 2000 compliant.
The Company's operations could be adversely affected to the extent that firms
and suppliers would be unable to provide services, materials or products.
 
    To the extent that Year 2000 compliance assurances are not given by the
Company's third party service providers and suppliers, the Company intends to
devise contingency plans to address any potential negative effects in the event
of the unavailability of services, materials or products. If necessary, the
Company may increase inventory levels of materials and products prior to
December 1999 as a contingency against possible disruption of supply.
Nevertheless, a failure of any contingency plan devised by the
 
                                       32
<PAGE>
Company may not prevent a business interruption caused by one or more of its
third party service providers or suppliers, and such a failure may have a
material adverse effect on the Company.
 
    Expenditures to date have not been material and have consisted solely of the
time of certain company personnel. The Company does not currently expect that
future costs of completing the assessment will be material.
 
RESULTS OF OPERATIONS
 
YEARS ENDED DECEMBER 31, 1998 AND 1997
 
    REVENUES.  Total revenues in the year ended December 31, 1998 were
$1,634,000 compared to $2,733,000 in the year ended December 31, 1997, a
decrease of $1,099,000 or 40.2%. The revenue earned in the year ended December
31, 1998 consisted of $1,107,000 in research support funding from the Bristol-
Myers Squibb and Merck collaborations; and $528,000 in SBIR funding. The revenue
earned in the year ended December 31, 1997 consisted of $2,025,000 in research
support funding from the Bristol-Myers Squibb, Merck and Pfizer collaborations;
a $500,000 milestone payment from the Bristol-Myers Squibb collaboration; and
$208,000 in SBIR funding. The decrease in revenues in the year ended December
31, 1998 as compared to the year ended December 31, 1997 was primarily due to
the decrease of research support funding from Merck during 1998; the decrease of
research support funding due to the termination of the Pfizer collaboration in
1997; and the lack of milestone payments from the Bristol-Myers Squibb
collaboration during 1998.
 
    RESEARCH AND DEVELOPMENT EXPENSES.  Total research and development expenses
in the year ended December 31, 1998 were $10,489,000 compared to $9,341,000 in
the year ended December 31, 1997, an increase of $1,148,000 or 12.3%. The
increase was largely due to (i) increased consulting and manufacturing costs
related to daptomycin development, and (ii) the additional personnel and
purchases that are required by such development.
 
    GENERAL AND ADMINISTRATIVE EXPENSES.  General and administrative expenses in
the year ended December 31, 1998 were $3,495,000 compared to $3,292,000 in the
year ended December 31, 1997, an increase of $203,000 or 6.2%. The increase was
largely due to (i) increased costs related to personnel, (ii) increased
marketing and investor and public relations expenses, and (iii) increased
consulting and license expenses.
 
    INTEREST INCOME AND EXPENSE.  Interest income in the year ended December 31,
1998 was $859,000 compared to $1,039,000 in year ended December 31, 1997, a
decrease of $180,000 or 17.3%. The decrease in interest income was due primarily
to a lower average cash, cash equivalent and investment balances
 
                                       33
<PAGE>
during the year ended December 31, 1998 as compared to the year ended December
31, 1997. Interest expense in the year ended December 31, 1998 was $334,000 as
compared to $237,000 during the year ended December 31, 1997, an increase of
$97,000 or 40.9%, due to additional leasing arrangements during the year.
 
    OTHER INCOME.  Other income in the year ended December 31, 1997 was
$1,833,000 and consisted entirely of gain on the sale of the Company's equity
position in Novalon.
 
    NET LOSS.  The net loss for the year ended December 31, 1998 was $11,825,000
compared to $7,265,000 during the year ended December 31, 1997, an increase of
$4,560,000 or 62.8%. The increase was primarily due to (i) a decrease in
revenues during the year ended December 31, 1998, as described above, (ii) an
increase in expenses incurred associated with the development of daptomycin,
(iii) and increased costs associated with the Company's marketing and investor
relations program.
 
RESULTS OF OPERATIONS
 
YEARS ENDED DECEMBER 31, 1997 AND 1996
 
    REVENUES.  Total revenues in the year ended December 31, 1997 were
$2,733,000 compared to $4,985,000 in the year ended December 31, 1996, a
decrease of $2,252,000 or 45.2%. The revenue earned in the year ended December
31, 1997 consisted of $2,025,000 in research support funding from the Bristol-
Myers Squibb, Merck and Pfizer collaborations; a $500,000 milestone payment from
the Bristol-Myers Squibb collaboration; and $208,000 in SBIR funding. The
revenue earned in the year ended December 31, 1996 primarily consisted of a
$1,500,000 technology licensing fee from the Merck collaboration; $2,116,000 in
research support funding from the Bristol-Myers Squibb, Merck and Pfizer
collaborations; $1,000,000 in milestone payments from the Bristol-Myers Squibb
collaboration; and $369,000 in SBIR funding. The decrease in revenues in the
year ended December 31, 1997 as compared to the year ended December 31, 1996 was
primarily due to the one-time technology license fee from Merck in the amount of
$1,500,000 in 1996; the decrease of research support funding primarily due to
the termination of the Pfizer collaboration in 1997; and reduced milestone
payments from the Bristol-Myers Squibb collaboration during 1997.
 
    RESEARCH AND DEVELOPMENT EXPENSES.  Total research and development expenses
in the year ended December 31, 1997 were $9,341,000 compared to $6,871,000 in
the year ended December 31, 1996, an increase of $2,470,000 or 35.9%. The
increase was largely due to (i) amortization of the Company's purchase option in
Novalon, (ii) purchases of laboratory research supplies associated with
additional equipment, and (iii) a license fee associated with worldwide rights
to develop, manufacture and market
 
                                       34
<PAGE>
daptomycin and expenses associated with the development and manufacture of
daptomycin from Eli Lilly, and (iv) increased personnel and related supplies
engaged in the research and development programs.
 
    GENERAL AND ADMINISTRATIVE EXPENSES.  General and administrative expenses in
the year ended December 31, 1997 were $3,292,000 compared to $1,989,000 in the
year ended December 31, 1996, an increase of $1,303,000 or 65.5%. The increase
was largely due to (i) increased costs related to additional executive staff
personnel and recruiting, (ii) increased costs of premiums for directors' and
officers' insurance, (iii) increased investor and public relation expenses and
(iv) increased legal expenses primarily associated with licensing and patent
activities.
 
    INTEREST INCOME AND EXPENSE.  Interest income in the year ended December 31,
1997 was $1,039,000 compared to $306,000 in year ended December 31, 1996, an
increase of $733,000 or 239.5%. The increase in interest income was due
primarily to higher average cash, cash equivalent and investment balances during
the year ended December 31, 1997 as compared to the year ended December 31,
1996. Interest expense in the year ended December 31, 1997 was $237,000 as
compared to $229,000 during the year ended December 31, 1996.
 
    OTHER INCOME.  Other income in the year ended December 31, 1997 was
$1,833,000 and consisted entirely of gain on the sale of the Company's equity
position in Novalon.
 
    NET LOSS.  The net loss for the year ended December 31, 1997 was $7,265,000
compared to $3,799,000 during the year ended December 31, 1996, an increase of
$3,466,000 or 91.2%. The increase, which was offset in part by the gain on the
sale of the Company's equity position in Novalon, was primarily due to (i) a
decrease in revenues during the year ended December 31, 1997, as described
above, (ii) an increase in expenses incurred by the Company to support the
advancement of the Company's internal research programs, (iii) an increase in
expenses incurred associated with the licensing of daptomycin from Eli Lilly,
(iv) amortization expense incurred by the Company associated with its investment
in Novalon and (v) increased costs associated with the Company's investor and
public relations program.
 
LIQUIDITY AND CAPITAL RESOURCES
 
    Since inception, the Company has financed its operations through the sale of
equity securities, equipment financing, sponsored research revenues, license
revenues and interest earned on invested capital. The Company's total cash, cash
equivalent and investments balance at December 31, 1998 was $19,012,000 compared
to $18,116,000 at December 31, 1997.
 
                                       35
<PAGE>
    Through December 31, 1998, the Company had invested an aggregate of
$7,728,000 (of which $1,835,000 was invested during the year then ended) in
property and equipment, primarily in facility renovations and laboratory
equipment under capital leases. The obligations under capital leases at December
31, 1998 were $1,918,000. Minimum annual principal payments due under capital
leases total $843,000 in 1999. Principal payments are scheduled to decline each
year thereafter until expiration in 2002. The Company made principal payments
under its capital lease obligations of $577,000 in the year ended December 31,
1998. The Company expects its capital expenditures in 1999 to be approximately
$800,000, consisting of laboratory and other equipment purchases.
 
    On September 23, 1998, the Company completed a private placement financing
with investors and raised approximately $12.7 million (net of financing costs of
$901,000) by issuing 6,065,560 shares at $2.25 per share, along with 3,032,783
warrants exercisable for Common Stock at $2.25 per share. The Company has filed
an S-3 registration statement to register the resale of the 9,098,343 shares of
Common Stock related to this financing. The proceeds of this private offering
will be used primarily to fund the clinical development of daptomycin and the
development of its proprietary genomic target validation and assay development
(VITA-TM-) technology.
 
    On February 3, 1999, the Company entered into a research and license
agreement with Novartis Pharma AG ("Novartis") to use the Company's proprietary
VITA-TM- technology to validate and develop assays for antiinfective targets and
to identify new compounds for development as antiinfective agents. In exchange
for such license, Novartis will pay the Company certain research payments and if
certain scientific and development milestones are achieved, Novartis will make
milestone payments. In addition, Novartis will be required to pay royalties to
the Company on worldwide sales of any drug developed and commercialized from any
products derived from this collaboration. Upon the signing of the research and
license agreement, Novartis purchased, and the Company issued to Novartis,
797,488 shares of Common Stock for a total purchase price of $4.0 million in
cash. The proceeds from the sale of these shares will be primarily used to fund
the clinical development of daptomycin and development of the VITA-TM-
technology.
 
    The Company believes that its existing capital resources, interest income
and future revenues due under the Novartis, Bristol-Myers Squibb and Merck
collaborative agreements will be sufficient to fund its operating expenses and
capital requirements as currently planned through 1999. The Company's actual
cash requirements may vary materially from those now planned and will depend on
numerous factors. There can be no assurance that the Company's existing cash,
cash equivalents, other capital resources, interest income and future revenues
due under the Novartis, Bristol-Myers Squibb and Merck collaborative agreements
will be sufficient to fund its operating expenses and capital requirements
during such period. Thereafter, the Company will need to raise substantial
additional capital to fund its operations.
 
                                       36
<PAGE>
The Company intends to seek such additional funding through public or private
financing or collaborative or other arrangements with corporate partners.
 
RECENT PRONOUNCEMENTS
 
    In June 1998, the Financial Accounting Standards Board issued Statement of
Financial Accounting Standards No. 133 ("SFAS 133") "Accounting for Derivative
Instruments and Hedging Activities" which is effective for fiscal years
beginning after June 15, 1999. The statement establishes accounting and
reporting standards requiring that every derivative instrument be recorded in
the balance sheet as either an asset or liability measured at its fair value.
SFAS No. 133 also requires that changes in the derivative's fair value be
recognized currently in earnings unless specific hedge accounting criteria are
met. Adoption of this standard is not expected to have a material impact on the
financial position or results of operations of the Company.
 
ITEM 7A. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK
 
    The Company owns financial instruments that are sensitive to market risks as
part of its investment portfolio. The investment portfolio is used to preserve
the Company's capital until it is required to fund operations, including the
Company's research and development activities. None of these market-risk
sensitive instruments are held for trading purposes. The Company does not own
derivative financial instruments in its investment portfolio. The investment
portfolio contains instruments that are subject to the risk of a decline in
interest rates.
 
    Interest Rate Risk--The Company's investment portfolio includes investment
grade debt instruments. These bonds are subject to interest rate risk, and could
decline in value if interest rates fluctuate. Due to the short duration and
conservative nature of these instruments, the Company does not believe that it
has a material exposure to interest rate risk.
 
                                       37
<PAGE>
ITEM 8. FINANCIAL STATEMENTS
 
                          CUBIST PHARMACEUTICALS, INC.
                         INDEX TO FINANCIAL STATEMENTS
 
<TABLE>
<CAPTION>
                                                                                                                PAGE
                                                                                                                -----
<S>                                                                                                          <C>
Report of Independent Accountants..........................................................................          39
 
Balance Sheets as of December 31, 1998 and 1997............................................................          40
 
Statements of Operations for the years ended December 31, 1998, 1997 and 1996..............................          42
 
Statements of Cash Flows for the years ended December 31, 1998, 1997 and 1996..............................          43
 
Statements of Changes in Stockholders' Equity for the years ended December 31, 1998, 1997 and 1996.........          45
 
Notes to Financial Statements..............................................................................          47
</TABLE>
 
                                       38
<PAGE>
                       REPORT OF INDEPENDENT ACCOUNTANTS
 
To the Board of Directors and Stockholders of Cubist Pharmaceuticals, Inc.:
 
In our opinion, the accompanying financial statements present fairly, in all
material respects, the financial position of Cubist Pharmaceuticals, Inc. as of
December 31, 1998 and 1997, and the results of its operations and its cash flows
for each of the three years in the period ended December 31, 1998 in conformity
with generally accepted accounting principles. These financial statements are
the responsibility of the Company's management; our responsibility is to express
an opinion on these financial statements based on our audits. We conducted our
audits of these financial statements in accordance with generally accepted
auditing standards which require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free of material
misstatement. An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements, assessing the
accounting principles used and significant estimates made by management, and
evaluating the overall financial statement presentation. We believe that our
audits provide a reasonable basis for the opinion expressed above.
 
                                          /s/ PricewaterhouseCoopers LLP
 
Boston, Massachusetts
February 15, 1999
 
                                       39
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                                 BALANCE SHEETS
 
<TABLE>
<CAPTION>
                                                                                             DECEMBER 31,
                                                                                     ----------------------------
<S>                                                                                  <C>            <C>
                                                                                         1998           1997
                                                                                     -------------  -------------
ASSETS
Current Assets:
  Cash and cash equivalents........................................................  $   6,463,688  $   2,837,600
  Short-term investments...........................................................      8,692,514      6,709,623
  Accounts receivable..............................................................             --         53,333
  Prepaid expenses and other current assets........................................        231,409        142,635
                                                                                     -------------  -------------
  Total current assets.............................................................     15,387,611      9,743,191
Property and equipment.............................................................      7,727,821      5,893,101
  Less: Accumulated depreciation and amortization..................................     (3,908,054)    (2,712,341)
                                                                                     -------------  -------------
  Property and equipment, net......................................................      3,819,767      3,180,760
Long-term investments..............................................................      3,855,336      8,569,107
Other assets.......................................................................         74,238        180,294
                                                                                     -------------  -------------
    Total assets...................................................................  $  23,136,952  $  21,673,352
                                                                                     -------------  -------------
                                                                                     -------------  -------------
</TABLE>
 
                                       40
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                           BALANCE SHEETS (CONTINUED)
 
<TABLE>
<CAPTION>
                                                                                             DECEMBER 31,
                                                                                     ----------------------------
                                                                                         1998           1997
                                                                                     -------------  -------------
<S>                                                                                  <C>            <C>
LIABILITIES AND STOCKHOLDERS' EQUITY
  Current Liabilities:
  Accounts payable.................................................................  $     460,939  $     275,260
  Accrued expenses.................................................................        572,562        492,304
  Current portion of long-term debt................................................         83,957        189,730
  Current portion of capital lease obligations.....................................        625,450        548,351
                                                                                     -------------  -------------
    Total current liabilities......................................................      1,742,908      1,505,645
Long-term debt, net of current portion.............................................         16,109        100,072
Long-term capital lease obligation, net of current portion.........................      1,292,165      1,004,969
                                                                                     -------------  -------------
    Total liabilities..............................................................      3,051,182      2,610,686
                                                                                     -------------  -------------
 
Commitments (Notes F, J, &K)
 
Stockholders' Equity:
Preferred Stock non-cumulative; convertible, $.001 par value; authorized 5,000,000
  shares, 1998 and 1997; issued and outstanding 1998 and 1997 no shares............             --             --
Common Stock, $.001 par value; authorized 25,000,000 shares, 1998 and 1997; issued
  and outstanding 1998 16,642,968 shares; issued and outstanding 1997 10,580,555
  shares...........................................................................         16,643         10,581
Additional paid-in capital.........................................................     54,890,014     42,047,966
Accumulated deficit................................................................    (34,820,887)   (22,995,881)
                                                                                     -------------  -------------
    Total stockholders' equity.....................................................     20,085,770     19,062,666
                                                                                     -------------  -------------
    Total liabilities and stockholders' equity.....................................  $  23,136,952  $  21,673,352
                                                                                     -------------  -------------
                                                                                     -------------  -------------
</TABLE>
 
    The accompanying notes are an integral part of the financial statements.
 
                                       41
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                            STATEMENTS OF OPERATIONS
 
<TABLE>
<CAPTION>
                                                                            FOR THE YEARS ENDED DECEMBER 31,
                                                                      --------------------------------------------
<S>                                                                   <C>             <C>            <C>
                                                                           1998           1997           1996
                                                                      --------------  -------------  -------------
Sponsored research revenues.........................................  $    1,634,199  $   2,733,083  $   4,985,052
Operating expenses:
  Research and development..........................................      10,489,258      9,340,928      6,871,149
  General and administrative........................................       3,495,264      3,292,241      1,989,284
                                                                      --------------  -------------  -------------
    Total operating expenses........................................      13,984,522     12,633,169      8,860,433
Interest income.....................................................         858,919      1,038,532        306,017
Interest expense....................................................        (333,602)      (237,119)      (229,305)
Other income........................................................              --      1,833,334             --
                                                                      --------------  -------------  -------------
  Net loss..........................................................  $  (11,825,006) $  (7,265,339) $  (3,798,669)
                                                                      --------------  -------------  -------------
                                                                      --------------  -------------  -------------
  Net comprehensive loss............................................  $  (11,825,006) $  (7,265,339) $  (3,798,669)
                                                                      --------------  -------------  -------------
                                                                      --------------  -------------  -------------
Basic and diluted net loss per common share.........................  $        (0.97) $       (0.73) $       (1.49)
                                                                      --------------  -------------  -------------
                                                                      --------------  -------------  -------------
Weighted average number of common shares for basic and diluted net
  loss per common share.............................................      12,224,404      9,994,718      2,553,999
                                                                      --------------  -------------  -------------
                                                                      --------------  -------------  -------------
</TABLE>
 
    The accompanying notes are an integral part of the financial statements.
 
                                       42
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                            STATEMENTS OF CASH FLOWS
 
<TABLE>
<CAPTION>
                                                                          FOR THE YEARS ENDED DECEMBER 31,
                                                                    ---------------------------------------------
<S>                                                                 <C>             <C>            <C>
                                                                         1998           1997            1996
                                                                    --------------  -------------  --------------
Cash flows for (from) operating activities:
  Net loss........................................................  $  (11,825,006) $  (7,265,339) $   (3,798,669)
  Adjustments to reconcile net loss to net cash used in operating
    activities:
    Gain on sale of equity interest...............................              --     (1,833,334)             --
    Amortization of equity interest...............................              --        833,334              --
    Depreciation and amortization.................................       1,243,596      1,057,887         740,408
    Changes in assets and liabilities:
      Accounts receivable.........................................          53,333        451,934         482,733
      Prepaid expenses and other current assets...................         (88,774)       144,007        (219,646)
      Other assets................................................         106,056         (6,495)        (15,228)
      Accounts payable and accrued expenses.......................         265,937       (458,577)        911,622
      Deferred revenue............................................              --       (126,900)        126,900
                                                                    --------------  -------------  --------------
        Total adjustments.........................................       1,580,148         61,856       2,026,789
                                                                    --------------  -------------  --------------
Net cash used for operating activities............................     (10,244,858)    (7,203,483)     (1,771,880)
                                                                    --------------  -------------  --------------
Cash flows for (from) investing activities:
  Purchase of equipment...........................................      (1,795,285)      (899,810)       (640,329)
  Leasehold improvements..........................................         (39,435)       (94,753)       (423,256)
  Purchase of equity interest.....................................              --     (1,000,000)             --
  Proceeds from sale of equity interest...........................              --      2,000,000              --
  Purchase of short-term investments..............................      (8,692,514)   (22,686,443)             --
  Maturities of short-term investments............................       6,709,623     15,976,820       1,006,569
  Purchase of long-term investments...............................      (3,855,336)    (8,569,107)             --
  Maturities of long-term investments.............................       8,569,107             --              --
                                                                    --------------  -------------  --------------
Net cash provided by (used for) investing activities..............         896,160    (15,273,293)        (57,016)
                                                                    --------------  -------------  --------------
</TABLE>
 
                                       43
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                      STATEMENTS OF CASH FLOWS (CONTINUED)
 
<TABLE>
<CAPTION>
                                                                          FOR THE YEARS ENDED DECEMBER 31,
                                                                    ---------------------------------------------
                                                                         1998           1997            1996
                                                                    --------------  -------------  --------------
<S>                                                                 <C>             <C>            <C>
Cash flows for (from) financing activities:
  Issuance of stock...............................................      12,770,227      5,942,697      19,146,448
  Proceeds from notes receivable..................................          30,000             --              --
  Repayments of debt..............................................        (189,736)      (189,943)       (168,565)
  Proceeds from capital lease financing...........................         941,255        927,686         599,593
  Principal payments of capital lease obligations.................        (576,960)      (695,417)       (468,782)
                                                                    --------------  -------------  --------------
Net cash provided by financing activities.........................      12,974,786      5,985,023      19,108,694
                                                                    --------------  -------------  --------------
Net increase (decrease) in cash and cash equivalents..............       3,626,088    (16,491,753)     17,279,798
Cash and cash equivalents at beginning of year....................       2,837,600     19,329,353       2,049,555
                                                                    --------------  -------------  --------------
Cash and cash equivalents at end of year..........................  $    6,463,688  $   2,837,600  $   19,329,353
                                                                    --------------  -------------  --------------
                                                                    --------------  -------------  --------------
Supplemental disclosures of cash flow information:
  Cash paid during the year for interest..........................  $      333,602  $     237,119  $      229,305
Non cash activity:
  Cancellation of promissory note in connection with resignation
    of officer (Note H)...........................................  $       37,776             --              --
</TABLE>
 
    The accompanying notes are an integral part of the financial statements.
 
                                       44
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                 STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY
 
              FOR THE YEARS ENDED DECEMBER 31, 1998, 1997 AND 1996
<TABLE>
<CAPTION>
                                                                                                                   $
                                                                                                               ADDITIONAL
                                                                                                                PAID-IN
                                                                                                                CAPITAL
                                                                                                               ----------
                                                                                                                ISSUANCE
                    # OF SHARES  # OF SHARES  # OF SHARES  # OF SHARES  # OF SHARES       $            $           OF
                    PREFERRED A  PREFERRED B  PREFERRED C  PREFERRED D    COMMON      PREFERRED     COMMON       SHARES
                    -----------  -----------  -----------  -----------  -----------  -----------  -----------  ----------
<S>                 <C>          <C>          <C>          <C>          <C>          <C>          <C>          <C>
12/31/95
  Balance.........   5,000,000   14,733,370   15,017,813           --    1,016,662    $  34,751    $   1,017   $17,004,210
                    -----------  -----------  -----------               -----------  -----------  -----------  ----------
                    -----------  -----------  -----------               -----------  -----------  -----------  ----------
Series D Preferred
  Stock par $001
  at $1.42 share,
  net of
  expenses........                                          2,816,902                     2,817                 3,941,727
Conversion of
  Preferred Stock
  to Common Stock
  par $.001.......  (5,000,000)  (14,733,370) (15,017,813) (2,816,902)   5,366,849      (37,568)       5,367       32,201
Exercise of Stock
  Options.........                                                          58,244                        58       35,232
Repurchase of
  Common Stock....                                                         (36,634)                      (37)     (12,273)
Initial Public
  Offering, net of
  expenses........                                                       3,139,252                     3,139   15,151,343
Forgiveness of
  Promissory
  Notes...........
Issuance of Common
  Stock Options
  and Warrants....                                                                                                101,378
Amortization of
  Deferred
  Compensation....
Net Loss..........
                                                                        -----------  -----------  -----------  ----------
12/31/96
  Balance.........          --           --           --           --    9,544,373           --    $   9,544   $36,253,818
                                                                        -----------  -----------  -----------  ----------
                                                                        -----------  -----------  -----------  ----------
Exercise of Stock
  Options.........                                                          57,981                 $      58   $  119,320
Repurchase of
  Common Stock....                                                          (1,390)                       (1)        (519)
Issuance of Common
  Stock, net of
  offering
  expenses........                                                         979,591                       980    5,902,859
Amortization of
  Deferred
  Compensation....
Forgiveness of
  Promissory
  Notes...........
Net Loss..........
                                                                        -----------               -----------  ----------
12/31/97
  Balance.........          --           --           --           --   10,580,555           --    $  10,581   $42,275,478
                                                                        -----------               -----------  ----------
                                                                        -----------               -----------  ----------
 
<CAPTION>
 
                                                     $             $
                       NOTES       DEFERRED     ACCUMULATED   STOCKHOLDERS'
                    RECEIVABLE   COMPENSATION     DEFICIT        EQUITY
                    -----------  -------------  ------------  ------------
<S>                 <C>          <C>            <C>           <C>
12/31/95
  Balance.........   $(178,901)    $ (34,431)   ($11,931,873)  $4,894,773
                    -----------  -------------  ------------  ------------
                    -----------  -------------  ------------  ------------
Series D Preferred
  Stock par $001
  at $1.42 share,
  net of
  expenses........                                              3,944,544
Conversion of
  Preferred Stock
  to Common Stock
  par $.001.......                                                      0
Exercise of Stock
  Options.........                                                 35,290
Repurchase of
  Common Stock....                                                (12,310)
Initial Public
  Offering, net of
  expenses........                                             15,154,482
Forgiveness of
  Promissory
  Notes...........      24,442                                     24,442
Issuance of Common
  Stock Options
  and Warrants....                  (101,378)                           0
Amortization of
  Deferred
  Compensation....                    56,058                       56,058
Net Loss..........                               (3,798,669)   (3,798,669)
                    -----------  -------------  ------------  ------------
12/31/96
  Balance.........   $(154,459)    $ (79,751)   ($15,730,542)  $20,298,610
                    -----------  -------------  ------------  ------------
                    -----------  -------------  ------------  ------------
Exercise of Stock
  Options.........                                             $  119,378
Repurchase of
  Common Stock....                                                   (520)
Issuance of Common
  Stock, net of
  offering
  expenses........     (80,000)                                 5,823,839
Amortization of
  Deferred
  Compensation....      20,000        43,924                       63,924
Forgiveness of
  Promissory
  Notes...........      22,774                                     22,774
Net Loss..........                               (7,265,339)   (7,265,339)
                    -----------  -------------  ------------  ------------
12/31/97
  Balance.........   $(191,685)    $ (35,827)   ($22,995,881)  $19,062,666
                    -----------  -------------  ------------  ------------
                    -----------  -------------  ------------  ------------
</TABLE>
 
    The accompanying notes are an integral part of the financial statements.
 
                                       45
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
           STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (CONTINUED)
 
              FOR THE YEARS ENDED DECEMBER 31, 1998, 1997 AND 1996
<TABLE>
<CAPTION>
                                                                                                                   $
                                                                                                               ADDITIONAL
                                                                                                                PAID-IN
                                                                                                                CAPITAL
                                                                                                               ----------
                                                                                                                ISSUANCE
                    # OF SHARES  # OF SHARES  # OF SHARES  # OF SHARES  # OF SHARES       $            $           OF
                    PREFERRED A  PREFERRED B  PREFERRED C  PREFERRED D    COMMON      PREFERRED     COMMON       SHARES
                    -----------  -----------  -----------  -----------  -----------  -----------  -----------  ----------
<S>                 <C>          <C>          <C>          <C>          <C>          <C>          <C>          <C>
Exercise of Stock
  Options.........                                                           2,576                 $       3   $    4,140
Shares issued in
  connection with
  employee stock
  purchase plan...                                                           6,341                         6       20,553
Repurchase of
  Common Stock....                                                          (2,064)                       (2)        (786)
Issuance of Common
  Stock, net of
  offering
  expenses........                                                       6,065,560                     6,065   12,774,811
Amortization of
  Deferred
  Compensation....                                                                                                  2,255
Repayment of
  Promissory
  Notes...........
Cancellation of
  Promissory Note
  in connection
  with resignation
  of officer......                                                         (10,000)                      (10)     (37,766)
Net Loss..........
                                                                        -----------               -----------  ----------
12/31/98
  Balance.........          --           --           --           --   16,642,968           --    $  16,643   $55,038,685
                                                                        -----------               -----------  ----------
                                                                        -----------               -----------  ----------
 
<CAPTION>
 
                                                     $             $
                       NOTES       DEFERRED     ACCUMULATED   STOCKHOLDERS'
                    RECEIVABLE   COMPENSATION     DEFICIT        EQUITY
                    -----------  -------------  ------------  ------------
<S>                 <C>          <C>            <C>           <C>
Exercise of Stock
  Options.........                                             $    4,143
Shares issued in
  connection with
  employee stock
  purchase plan...                                                 20,559
Repurchase of
  Common Stock....                                                   (788)
Issuance of Common
  Stock, net of
  offering
  expenses........                                             12,780,876
Amortization of
  Deferred
  Compensation....      22,223       (11,158)                      13,320
Repayment of
  Promissory
  Notes...........      30,000                                     30,000
Cancellation of
  Promissory Note
  in connection
  with resignation
  of officer......      37,776                                          0
Net Loss..........                              (11,825,006)  (11,825,006)
                    -----------  -------------  ------------  ------------
12/31/98
  Balance.........   $(101,686)    $ (46,985)   ($34,820,887)  $20,085,770
                    -----------  -------------  ------------  ------------
                    -----------  -------------  ------------  ------------
</TABLE>
 
    The accompanying notes are an integral part of the financial statements.
 
                                       46
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                         NOTES TO FINANCIAL STATEMENTS
 
A. NATURE OF BUSINESS
 
    Cubist Pharmaceuticals, Inc. ("Cubist" or the "Company") is a
biopharmaceutical company founded in May 1992 and is engaged in the research,
development and commercialization of novel classes of antiinfective drugs to
treat infectious diseases caused by bacteria and fungi. Cubist has established
multiple technology licenses and collaborations and has established a network of
advisors and collaborators. The Company is located in Cambridge, Massachusetts.
 
B. ACCOUNTING POLICIES
 
    BASIS OF PRESENTATION
 
    The accompanying financial statements are stated on an accrual basis.
 
    USE OF ESTIMATES
 
    The preparation of financial statements in conformity with generally
accepted accounting principles requires management to make certain estimates and
assumptions that affect the reported amounts of assets and liabilities, and
disclosure of contingent assets and liabilities at the date of the financial
statements and the reported amounts of revenues and expenses during the reported
period. Actual results could differ from those estimates.
 
    RISKS AND UNCERTAINTIES
 
    The Company is subject to risks common to companies in the industry
including, but not limited to, development by the Company or its competitors of
new technological innovations, uncertainty of product development and
commercialization, lack of marketing and sales history, dependence on key
personnel, market acceptance of products, product liability, dependence on
information technology, protection of proprietary technology, ability to raise
additional financing, and compliance with FDA and other governmental
regulations.
 
                                       47
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
B. ACCOUNTING POLICIES (CONTINUED)
    CASH EQUIVALENTS
 
    Cash equivalents consist of short-term interest-bearing instruments (U.S.
Government treasuries and money market accounts) with original maturities of
three months or less. These investments are carried at cost which approximates
market value.
 
    SHORT-TERM INVESTMENTS
 
    Short-term investments, with an original maturity of more than three months
and less than one year when purchased, consisted of certificates of deposit and
investment-grade commercial paper at December 31, 1998 and 1997. Short-term
investments, all of which are held to maturity, are stated at amortized cost
plus accrued interest, which approximates market value.
 
    LONG-TERM INVESTMENTS
 
    Long-term investments, with a maturity of more than twelve months when
purchased, consisted of investment-grade corporate debt at December 31, 1998 and
1997. Long-term investments, all of which are held to maturity, are stated at
amortized cost plus accrued interest, which approximates market value.
 
    PROPERTY AND EQUIPMENT
 
    Property and equipment are recorded at cost. Depreciation is provided using
the straight-line method over the estimated useful lives of the related assets,
generally three years for computer equipment and five years for laboratory
equipment, furniture and fixtures. Leasehold improvements are stated at cost and
are amortized over the lesser of the life of the lease or their estimated useful
lives. The leasehold improvements are also utilized as collateral up to a value
of $100,066, which relates to the balance of long-term debt. Maintenance and
repairs are charged to expense as incurred, while major betterments are
capitalized. When assets are retired or otherwise disposed of, the assets and
related allowances for depreciation and amortization are eliminated from the
accounts and any resulting gain or loss is reflected in income.
 
                                       48
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
B. ACCOUNTING POLICIES (CONTINUED)
    RESEARCH AND DEVELOPMENT
 
    All research and development costs are expensed as incurred.
 
    INCOME TAXES
 
    Research and experimentation and other tax credits, when utilized, will be
recorded using the flow-through method of accounting as a reduction of the
current provision for federal and state income taxes.
 
    EARNINGS PER SHARE
 
    Effective December 31, 1997, the Company adopted Statement of Financial
Accounting Standards No. 128 (SFAS 128) "Earnings Per Share", which required the
disclosure of Basic Earnings per Common Share and Diluted Earnings per Common
Share for all periods presented. At December 31, 1998, 1997, and 1996 the
Company had 1,519,094; 802,468; and 500,760 options outstanding, respectively.
At December 31, 1998, 1997, and 1996 the Company had 3,119,402; 86,619; and
33,333 warrants outstanding, respectively. Adoption of this statement has not
affected the earnings per share amounts presented in any period because the
effect of including these equity instruments would be anti-dilutive.
 
    COMPREHENSIVE INCOME
 
    In 1997, the Financial Accounting Standards Board issued SFAS 130 "Reporting
Comprehensive Income," which is effective for periods beginning after December
15, 1997. The statement established standards for reporting and displaying
comprehensive income and its components (revenues, expenses, gains, and losses)
in a full set of general purpose financial statements. The statement required
that all components of comprehensive income be reported in a financial statement
that is displayed with the same prominence as other financial statements. The
Company has adopted SFAS 130. The adoption of this standard had no impact on the
financial statements.
 
                                       49
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
B. ACCOUNTING POLICIES (CONTINUED)
    BUSINESS SEGMENTS
 
    In 1997, the Financial Accounting Standards Board issued SFAS 131,
"Disclosures about Segments of an Enterprise and Related Information," which is
effective for periods beginning after December 15, 1997. The statement
established standards for reporting information about operating segments in
annual financial statements of public enterprises and in interim financial
reports issued to shareholders. It also established standards for related
disclosures about products and services, geographic areas and major customers.
The Company has adopted SFAS 131. The adoption of this standard had no impact on
the financial statements.
 
C. PROPERTY AND EQUIPMENT
 
    At December 31, property and equipment consisted of:
 
<TABLE>
<CAPTION>
                                                                                            1998          1997
                                                                                        ------------  ------------
<S>                                                                                     <C>           <C>
Leasehold improvements................................................................  $  2,623,924  $  2,584,489
Laboratory equipment..................................................................     4,047,291     2,389,683
Furniture and fixtures................................................................       319,245       286,197
Computer equipment....................................................................       737,361       632,732
                                                                                        ------------  ------------
                                                                                           7,727,821     5,893,101
                                                                                        ------------  ------------
Less accumulated depreciation and amortization........................................    (3,908,054)   (2,712,341)
                                                                                        ------------  ------------
Property and equipment, net...........................................................  $  3,819,767  $  3,180,760
                                                                                        ------------  ------------
                                                                                        ------------  ------------
</TABLE>
 
    Depreciation and amortization expense was $1,195,713; $971,189; and $659,908
in 1998, 1997 and 1996, respectively.
 
                                       50
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
D. ACCRUED EXPENSES
 
    At December 31, accrued expenses consisted of:
 
<TABLE>
<CAPTION>
                                                                                               1998        1997
                                                                                            ----------  ----------
<S>                                                                                         <C>         <C>
Payroll and benefits......................................................................  $  337,475  $  218,583
Vacation..................................................................................          --      67,837
Professional services.....................................................................      77,720     119,500
Annual report.............................................................................      50,000      35,000
Drug Development..........................................................................      86,820          --
Miscellaneous.............................................................................      20,547      51,384
                                                                                            ----------  ----------
Total accrued expenses....................................................................  $  572,562  $  492,304
                                                                                            ----------  ----------
                                                                                            ----------  ----------
</TABLE>
 
E. COLLABORATIVE RESEARCH AGREEMENTS
 
    On December 15, 1995, the Company entered into a collaborative research
agreement with Pfizer, Inc. Under the terms of the agreement, Pfizer paid the
Company a technology licensing fee upon execution and research support payments.
These payments were recognized as income earned under the terms of the
agreement. In addition, Pfizer reimbursed the Company for expenses related to
the screening of Pfizer compounds against the Company's targets and certain
milestone payments. These reimbursement payments were recognized as revenue as
the work was completed. The Company included in sponsored research revenues
$150,000 and $587,000 in 1997 and 1996, respectively, in accordance with the
agreement. On June 20, 1997, the Company's collaborative agreement with Pfizer
expired pursuant to its own terms. Prior to such expiration, the Company had
received all of the research support payments and technology licensing fees that
the Company was entitled to receive under that collaborative agreement. In
accordance with the terms of that collaborative agreement, the Company selected
and licensed from Pfizer one of the chemical compounds that was identified and
characterized during the Company's collaboration with Pfizer. Pursuant to the
terms of that license, the Company may develop and commercialize such licensed
compound without further obligation to Pfizer.
 
    In June 1996, the Company entered into a collaborative research agreement
with Bristol-Myers Squibb Company ("Bristol-Myers Squibb"). Under the terms of
the agreement, Bristol-Myers Squibb
 
                                       51
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
E. COLLABORATIVE RESEARCH AGREEMENTS (CONTINUED)
purchased from the Company $4,000,000 of the Company's Preferred Stock upon
execution of the agreement, and has agreed to make payments to the Company upon
the achievement of certain milestones. These milestone payments are recognized
as income as earned under the terms of the agreement. In addition, Bristol-Myers
Squibb will reimburse the Company a fixed amount for research and development
expenses relating to the production of certain targets and also for expenses
relating to the screening of Bristol-Myers Squibb compounds against the
Company's targets over three years, with an option to fund a fourth year. These
reimbursements are to be paid at the beginning of each calendar quarter in
accordance with the agreement. The Company included in sponsored research
revenues $500,000 and $1,000,000 in milestone payments in 1997 and 1996,
respectively; and $1,000,000; $1,000,000 and $516,668 in 1998, 1997 and 1996,
respectively, for certain research and development revenues in accordance with
the agreement.
 
    In June 1996, the Company entered into a collaborative research agreement
with Merck & Co., Inc. ("Merck"). Under the terms of the agreement, Merck paid
the Company a technology licensing fee upon execution and will pay certain
milestone payments if earned. These payments are recognized as income as earned
under the terms of the agreement. In addition, Merck has reimbursed the Company
for research and development expenses relating to the production of certain
targets; for expenses relating to the screening of Merck compounds against the
Company's targets; and for expenses relating to compound optimization. These
payments are recognized as revenue as the work is completed. During 1996, the
Company included in sponsored research revenues $1,500,000 for the technology
licensing fee and $106,667, $875,233 and $1,012,300 in 1998, 1997 and 1996,
respectively, for certain research and development revenues in accordance with
the agreement.
 
    In May 1997, the Company acquired 333,333 shares of Series B Convertible
Preferred Stock of Novalon Pharmaceutical Corporation ("Novalon"), together with
an option to purchase all of the capital stock of Novalon. The aggregate
purchase price for such shares and such option was $1.0 million. The Company
allocated all of the $1.0 million aggregate purchase price to the option based
on management's estimates of the relative fair values of the option and the
shares of Series B Convertible Preferred Stock acquired. The value of the option
was amortized over the option period resulting in an $833,333 research and
development expense. On September 29, 1997, the Company agreed to terminate its
option to acquire Novalon and sold its existing equity position back to Novalon
for $2.0 million resulting in a gain of
 
                                       52
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
E. COLLABORATIVE RESEARCH AGREEMENTS (CONTINUED)
$1,833,333 included in other income. The Company will pay Novalon a percent of
revenues received by the Company that relates to the use of the technology.
 
F. LICENSE AGREEMENT
 
    On November 7, 1997, the Company entered into a license agreement with Eli
Lilly and Company ("Eli Lilly") pursuant to which the Company acquired exclusive
worldwide rights to develop, manufacture and market daptomycin. Daptomycin is a
natural product being developed for the treatment of STAPHYLOCOCCUS AUREUS and
enterococcus infections. In exchange for such license, the Company has paid an
upfront license fee in cash and, if certain drug development milestones are
achieved, has agreed to pay milestone payments by issuing shares of Common Stock
to Eli Lilly. In addition, the Company will be required to pay royalties to Eli
Lilly on worldwide sales of daptomycin.
 
G. FINANCING
 
    On September 23, 1998, the Company completed a private placement financing
with investors and raised approximately $12.7 million (net of financing costs of
approximately $901,000) by issuing 6,065,560 shares at $2.25 per share, along
with 3,032,783 warrants exercisable for Common Stock at $2.25 per share. The
warrants are exercisable at any time from September 23, 1998 until September 23,
2003. The value of the warrants and Common Stock in excess of par value have
been reflected in additional paid-in-capital. The Company has filed an S-3
registration statement to register 9,098,343 shares of Common Stock related to
this financing. The proceeds of this private offering will be used primarily to
fund the clinical development of daptomycin and the development of its
proprietary genomic target validation and assay development (VITA-TM-)
technology.
 
    On July 18, 1997, the Company completed a private equity financing in which
the Company raised $6.0 million before offering expenses of $96,161 by issuing
979,591 common shares at $6.125 per share. These shares were subsequently
registered with the Securities and Exchange Commission.
 
                                       53
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
H. STOCKHOLDERS' EQUITY
 
    WARRANTS
 
    Total warrants outstanding at December 31, 1998 were 3,119,402 (3,032,783
warrants relate to the financing described above in footnote G). On October 23,
1996, the Company amended 17,142 of warrants issued to both Drs. Rebek and
Schimmel in May 1995 to extend the expiration date of such warrants from the
effective date of the Company's initial public offering to May 15, 2005, and to
provide that the warrants will vest in four equal annual installments commencing
upon the first anniversary of their grant date. As a result of this amendment,
the Company recorded deferred compensation in the amount of $62,000 to be
amortized to the income statement over the remaining vesting period from October
1996 to May 1999.
 
    NOTES RECEIVABLE FROM RELATED PARTIES
 
    The Company has accepted a promissory note from the Chief Executive Officer
in consideration for the Preferred Stock issued to him. In 1997, the term of
this note was extended to fall due in equal quarterly installments of $10,000
commencing on March 31, 1998. The aggregate principal amount of this note at
December 31, 1998 is $101,686 and is reflected in stockholders' equity as a
reduction to paid-in capital.
 
    In 1997 the Company accepted a promissory note in the amount of $80,000 from
the Chief Business Officer in consideration for the Common Stock issued to him.
The note had an annual interest rate of 4% and fell due on May 19, 2000. The
note was to be forgiven in three equal annual installments, contingent upon the
Chief Business Officer's employment, from May 1998 to May 2000. In 1998, $22,223
was charged to General & Administration expense in relation to such forgiveness.
On October 23, 1998, in connection with the resignation of the officer, the
Common Stock was returned and retired, and the note was canceled.
 
I. STOCK OPTIONS
 
    The Company has a stock option plan under which options to purchase
3,000,000 shares of its Common Stock may be granted to employees, directors,
officers or consultants. The options are granted at fair market value on the
date of the grant as determined by the Board of Directors, vest ratably over a
four-year period and expire ten years from the date of grant. In addition, the
Company issued to certain consultants and directors non-qualified stock options
to purchase 143,926 shares of its Common Stock.
 
                                       54
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
I. STOCK OPTIONS (CONTINUED)
During 1995 and 1994, the Company allowed employees and consultants to exercise
their full grants to take advantage of certain favorable tax benefits. The
Company reserved the right to repurchase any unearned shares at the original
purchase price if the employee or consultant does not fulfill their vesting
requirement. 2,064; 1,390 and 36,634 shares of previously exercised options were
repurchased in 1998, 1997 and 1996, respectively, because vesting schedules were
not fulfilled.
 
    The Company adopted the disclosure provisions of SFAS 123, Accounting for
Stock Based Compensation, in 1996 and has applied APB Opinion 25 and related
Interpretations in accounting for its plans. Had compensation costs for the
Company's stock-based compensation plan been determined based on the fair value
at the grant dates as calculated in accordance with SFAS 123, the Company's net
loss and loss per share for the years ended December 31, 1998, 1997 and 1996
would have been increased to the pro forma amounts indicated below:
 
<TABLE>
<CAPTION>
                                       1998                               1997                              1996
                         ---------------------------------  --------------------------------  --------------------------------
                                         BASIC AND DILUTED                 BASIC AND DILUTED                 BASIC AND DILUTED
                            NET LOSS      LOSS PER SHARE      NET LOSS      LOSS PER SHARE      NET LOSS      LOSS PER SHARE
                         --------------  -----------------  -------------  -----------------  -------------  -----------------
<S>                      <C>             <C>                <C>            <C>                <C>            <C>
As Reported............  $  (11,825,006)     $   (0.97)     $  (7,265,339)     $   (0.73)     $  (3,798,669)     $   (1.49)
Pro forma..............  $  (13,019,532)     $   (1.07)     $  (7,859,006)     $   (0.79)     $  (4,053,670)     $   (1.59)
</TABLE>
 
    The fair value of each stock option was estimated on the date of grant using
Black-Scholes option-pricing model with the following weighted-average
assumptions: an expected life of four (4) years, expected volatility of 97%, a
dividend yield of 0% and a risk-free interest rate of 4.7% in 1998; an expected
life of four (4) years, expected volatility of 87%, a dividend yield of 0% and a
risk-free interest rate of 6.36% in 1997 and 1996. The effects of applying SFAS
123 in this pro forma disclosure are not indicative of future amounts.
Additional awards in future years are anticipated.
 
                                       55
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
I. STOCK OPTIONS (CONTINUED)
    A summary of the status of the Company's stock option plan as of December
31, 1998, 1997, 1996 and changes during each of the years then ended, is
presented below:
 
<TABLE>
<CAPTION>
                                                                 1998                     1997                    1996
                                                        -----------------------  ----------------------  ----------------------
                                                                       WAEP*                   WAEP*                   WAEP*
                                                          NUMBER     PER SHARE    NUMBER     PER SHARE    NUMBER     PER SHARE
                                                        ----------  -----------  ---------  -----------  ---------  -----------
<S>                                                     <C>         <C>          <C>        <C>          <C>        <C>
Balance at January 1..................................     802,468   $    4.69     500,760   $    1.93     159,057   $     .40
Granted...............................................     999,845        3.48     438,614        7.06     414,103        2.52
Exercised.............................................       2,576        1.61      56,591        2.06      21,610         .61
Canceled..............................................     280,643        7.17      80,315        2.29      50,790         .97
                                                        ----------       -----   ---------       -----   ---------       -----
Balance at December 31................................   1,519,094   $    3.44     802,468   $    4.69     500,760   $    1.93
                                                        ----------       -----   ---------       -----   ---------       -----
                                                        ----------       -----   ---------       -----   ---------       -----
Options exercisable at December 31....................     366,039   $    3.07     191,911   $    2.73      86,560   $    1.19
 
Weighted average grant-date fair value of options
  granted during the year.............................  $     2.42               $    5.41               $    2.52
</TABLE>
 
- ------------------------
 
*   Weighted-Average Exercise Price
 
The following table summarizes information about stock options outstanding at
December 31, 1998:
 
<TABLE>
<CAPTION>
                                                  OPTIONS OUTSTANDING
                                    -----------------------------------------------       OPTIONS EXERCISABLE
                                                    REMAINING                        ------------------------------
                                      NUMBER       CONTRACTUAL    WEIGHTED-AVERAGE     NUMBER     WEIGHTED-AVERAGE
RANGE OF EXERCISE PRICES            OUTSTANDING       LIFE         EXERCISE PRICE    EXERCISABLE   EXERCISE PRICE
- ----------------------------------  -----------  ---------------  -----------------  -----------  -----------------
<S>                                 <C>          <C>              <C>                <C>          <C>
$.007--$1.96......................     322,634       7.1 years        $    1.45         225,990       $    1.37
$2.25--$3.00......................     649,850       9.8 years             2.46           4,723            2.39
$5.25--$7.00......................     524,310       8.9 years             5.66         126,747            5.75
$8.00--$10.125....................      22,300       8.3 years             8.32           8,579            8.36
                                    -----------  ---------------          -----      -----------          -----
                                     1,519,094       8.8 years        $    3.44         366,039       $    3.07
                                    -----------  ---------------          -----      -----------          -----
                                    -----------  ---------------          -----      -----------          -----
</TABLE>
 
                                       56
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
J. LEASE COMMITMENTS
 
    The Company leases its facilities under an operating lease agreement which
expires on September 15, 2003 and is renewable at the Company's option for one
additional five-year period. Under the terms of the lease, the Company is
obligated to pay its prorated share of common operating expenses and real estate
taxes as well as base rents. In addition, the Company entered into an agreement
with the landlord under which the landlord provided financing to the Company for
a portion of the buildout cost ($543,393) at an interest rate of 12% per year
payable in equal monthly installments of $12,087 over five years through October
1998. The Company also provided a security deposit of $100,000 upon execution of
the lease. The security deposit bears interest in a segregated account, and was
partially refunded ($79,000 plus interest) on the fifth anniversary, and is
fully refundable plus interest within thirty days after the expiration of the
lease, provided no event of default has occurred. This agreement has been paid
in full as of December 31, 1998. The Company also financed an additional
$345,500 during the first quarter of 1995 relating to a 6,510 square foot
facility expansion completed during the first week of January 1995. This
additional debt is payable in equal monthly installments of $7,685 over five
years with an annual interest rate of 12% through February 2000. No additional
security deposit was required. At December 31, 1998, the outstanding principal
balance was $100,066.
 
    The Company leases certain equipment under long-term capital leases. The
cost of this equipment included in fixed assets was $4,204,410 at the end of
1998, with associated accumulated depreciation of $2,533,069 at December 31,
1998. The Company intends to purchase all of the leased equipment at a price
 
                                       57
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
J. LEASE COMMITMENTS (CONTINUED)
to be negotiated at lease end. Future lease payments for non-cancelable leases
for the respective years ended December 31 are as follows:
 
<TABLE>
<CAPTION>
                                                                                       OPERATING       CAPITAL
                                                                                        LEASES         LEASES
                                                                                     -------------  -------------
<S>                                                                                  <C>            <C>
  1999.............................................................................   $   207,679    $   842,544
  2000.............................................................................       207,679        685,846
  2001.............................................................................       207,679        564,210
  2002.............................................................................       207,679        330,090
  2003.............................................................................       147,101             --
  2004 and thereafter..............................................................            --             --
                                                                                     -------------  -------------
Total minimum lease payments.......................................................   $   977,817    $ 2,422,690
                                                                                     -------------  -------------
Less amount representing interest payments.........................................                     (505,075)
                                                                                                    -------------
Present value of minimum lease payments............................................                    1,917,615
Less current portion...............................................................                     (625,450)
                                                                                                    -------------
Long-term obligation...............................................................                  $ 1,292,165
                                                                                                    -------------
                                                                                                    -------------
</TABLE>
 
    Lease payments under operating leases were $312,228 in fiscal year 1998;
$246,498 in fiscal year 1997, and $248,784 in fiscal year 1996.
 
K. EMPLOYEE BENEFITS
 
    The Company instituted a 401(k) savings plan in 1993, in which substantially
all of its permanent employees are eligible to participate. Participants may
contribute up to 15% of their annual compensation to the plan, subject to
certain limitations. Prior to January 1, 1998, the Company contributed a
matching amount of up to 1.5% of a participant's total compensation or $500
annually, whichever is less. Effective January 1, 1998, participants were
granted a matching option in cash or company stock. The Company will match in
Common Stock up to 4.5% of a participant's total compensation or 75% of a
participant's total
 
                                       58
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
K. EMPLOYEE BENEFITS (CONTINUED)
contribution annually, whichever is less. Matches distributed in Common Stock
have immediate vesting. The Company contributed $6,160; $20,165 and $16,025,
during 1998, 1997 and 1996 respectively.
 
    The Company instituted an employee stock purchase plan in 1998, in which
substantially all of its permanent employees are eligible to participate.
Participants may contribute up to 15% of their annual compensation to the plan,
subject to certain limitations. The plan allows participants to purchase company
Common Stock, after a pre-determined six month period, through payroll
deductions at a price 15% less than the lower of the closing price for the
beginning or ending date of the purchase period.
 
L. INCOME TAXES
 
    The Company follows the liability method of accounting for income taxes in
accordance with the provisions of Statement of Financial Accounting Standards
(SFAS) No. 109, "Accounting for Income Taxes", whereby a deferred tax liability
is measured by the enacted tax rates which will be in effect when any
differences between the financial statements and tax basis of assets reverse.
The deferred tax liability can be reduced by net operating losses being carried
forward for tax purposes.
 
    The tax effects of temporary differences that give rise to significant
portions of the deferred tax assets and liabilities are presented below:
 
<TABLE>
<CAPTION>
                                                                         1998            1997           1996
                                                                    --------------  --------------  -------------
<S>                                                                 <C>             <C>             <C>
Net operating loss carryforwards..................................  $   10,715,000  $    5,780,000  $   4,376,000
Capitalized research and development..............................       2,350,000       2,690,000      1,700,000
Research and experimentation credits..............................       1,938,000       1,575,000        765,000
Other, net........................................................         609,000         377,000        306,000
                                                                    --------------  --------------  -------------
Total Deferred Tax Assets.........................................  $   15,612,000  $   10,422,000  $   7,147,000
                                                                    --------------  --------------  -------------
Valuation reserve.................................................  $  (15,612,000) $  (10,422,000) $  (7,147,000)
                                                                    --------------  --------------  -------------
                                                                    --------------  --------------  -------------
</TABLE>
 
    The company has a federal net operating loss carryforward of approximately
$27.2 million which begins to expire in 2007, and a state net operating loss
carryforward of $24.6 million which begins to expire in 1999. Research and
experimentation tax credits for federal and state purposes of $1,260,000 and
 
                                       59
<PAGE>
                          CUBIST PHARMACEUTICALS, INC.
 
                   NOTES TO FINANCIAL STATEMENTS (CONTINUED)
 
L. INCOME TAXES (CONTINUED)
$678,000, respectively begin to expire in 2008. The net operating loss and tax
credit carryforwards may be subject to an annual limitation as a result of the
change in ownership due to the initial public offering. The Company has
established a valuation reserve against the deferred tax benefit arising from
these carryforwards due to the uncertainty of earning sufficient taxable income
to receive the benefit and accordingly has not given recognition to these tax
benefits in these financial statements. These carryforwards are also subject to
review by the Internal Revenue Service.
 
M. RECENT PRONOUNCEMENTS
 
    In June 1998, the Financial Accounting Standards Board issued Statement of
Financial Accounting Standards No. 133 (SFAS 133) "Accounting for Derivative
Instruments and Hedging Activities" which is effective for fiscal years
beginning after June 15, 1999. The statement establishes accounting and
reporting standards requiring that every derivative instrument be recorded in
the balance sheet as either an asset or liability measured at its fair value.
SFAS No. 133 also requires that changes in the derivative's fair value be
recognized currently in earnings unless specific hedge accounting criteria are
met. Adoption of this standard is not expected to have a material impact on the
financial position or results of operations of the Company.
 
N. SUBSEQUENT EVENT
 
    On February 3, 1999, the Company entered into a research and license
agreement with Novartis Pharma AG ("Novartis") to use the Company's proprietary
VITA-TM- technology to validate and develop assays for antiinfective targets and
to identify new compounds for development as antiinfective agents. In exchange
for such license, Novartis will pay the Company certain research payments and,
if certain scientific and development milestones are achieved, Novartis will
make milestone payments. In addition, Novartis will be required to pay royalties
to the Company on worldwide sales of any drug developed and commercialized from
any products derived from this collaboration. Upon the signing of the research
and license agreement, Novartis purchased, and the Company issued to Novartis,
797,488 shares of Common Stock for a total purchase price of $4.0 million in
cash. The proceeds from the sale of these shares will be primarily used to fund
the clinical development of daptomycin and development of the VITA-TM-
technology.
 
                                       60
<PAGE>
ITEM 9. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND
        FINANCIAL DISCLOSURE
 
    None.
 
                                    PART III
 
ITEM 10. DIRECTORS AND EXECUTIVE OFFICERS OF THE REGISTRANT
 
    Information with respect to Directors and compliance with Section 16(a) of
the Securities Exchange Act may be found in the sections captioned "PROPOSAL NO.
1--ELECTION OF DIRECTORS", "EXECUTIVE COMPENSATION" and "SECTION 16(A)
BENEFICIAL OWNERSHIP REPORTING COMPLIANCE" appearing in the definitive Proxy
Statement to be delivered to Stockholders in connection with the Annual Meeting
of Stockholders to be held on June 1, 1999. Such information is incorporated
herein by reference. Information with respect to Executive Officers may be found
under the section captioned "Executive Officers of the Registrant" in Part I of
this Annual Report on Form 10-K.
 
ITEM 11. EXECUTIVE COMPENSATION
 
    The information required with respect to this item may be found in the
sections captioned "EXECUTIVE COMPENSATION" appearing in the definitive Proxy
Statement to be delivered to Stockholders in connection with the Annual Meeting
of Stockholders to be held on June 1, 1999. Such information is incorporated
herein by reference.
 
ITEM 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT
 
    The information required with respect to this item may be found in the
section captioned "PRINCIPAL STOCKHOLDERS" and "PROPOSAL NO. 1--ELECTION OF
DIRECTORS" appearing in the definitive Proxy Statement to be delivered to
Stockholders in connection with the Annual Meeting of Stockholders to be held on
June 1, 1999. Such information is incorporated herein by reference.
 
ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS
 
    The Information required with respect to this item may be found in the
section captioned "CERTAIN TRANSACTIONS" appearing in the definitive Proxy
Statement to be delivered to Stockholders in connection with the Annual Meeting
of Stockholders to be held on June 1, 1999. Such information is incorporated
herein by reference.
 
                                       61
<PAGE>
                                    PART IV
 
ITEM 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K
 
(A) DOCUMENTS FILED AS PART OF FORM 10-K
 
1. FINANCIAL STATEMENTS.
 
    The following financial statements and supplementary data are included in
Part II Item 8 filed as part of this report:
 
    - Report of Independent Accountants
 
    - Balance Sheets as of December 31, 1998 and 1997
 
    - Statements of Operations for the years ended December 31, 1998, 1997 and
      1996
 
    - Statements of Cash Flows for the years ended December 31, 1998, 1997 and
      1996
 
    - Statements of Stockholders' Equity for the years ended December 31, 1998,
      1997 and 1996
 
    - Notes to Financial Statements
 
2. FINANCIAL STATEMENT SCHEDULE.
 
    None.
 
    Schedules not listed above have been omitted because they are not
applicable, not required or the information required is shown in the financial
statements or the notes thereto.
 
3. LIST OF EXHIBITS
 
<TABLE>
<CAPTION>
EXHIBITS
- ---------
<C>        <S>
 
      3.3  Restated Certificate of Incorporation of the Registrant. (Exhibit 3.3, Registration No. 333-6795)
 
      3.4  Amended and Restated By-Laws of the Registrant, as amended to date. (Exhibit 3.4, Registration No.
           333-6795)
 
      4.1  Specimen certificate for shares of Common Stock. (Exhibit 4.1, Registration No. 333-6795)
 
    +10.1  Patent License Agreement between the Registrant and the Massachusetts Institute of Technology, dated
           March 10, 1994. (Exhibit 10.1, Registration No. 333-6795)
</TABLE>
 
                                       62
<PAGE>
<TABLE>
<CAPTION>
EXHIBITS
- ---------
<C>        <S>
    +10.2  License Agreement between the Registrant and the Board of Trustees of Leland Stanford Junior University,
           dated April 1, 1994. (Exhibit 10.2, Registration No. 333-6795)
 
     10.3  Employment Agreement between the Registrant and Scott M. Rocklage, dated June 20, 1994. (Exhibit 10.3,
           Registration No. 333-6795)
 
     10.4  Consulting Agreement between the Registrant and Paul R. Schimmel, dated May 1, 1992. (Exhibit 10.4,
           Registration No. 333-6795)
 
     10.5  Amended and Restated 1993 Stock Option Plan. (Exhibit 10.6, Registration No.333-6795)
 
    +10.6  Collaborative Research Agreement between the Registrant and Pfizer Inc., dated December 15, 1995.
           (Exhibit 10.7, Registration No. 333-6795)
 
     10.7  Letter Agreement, dated June 26, 1997, between the Company and Pfizer, Inc. (Exhibit 10.8, Registration
           No. 333-33883)
 
     10.8  Collaborative Research and License Agreement between the Registrant and Merck & Co., Inc., dated June
           13, 1996. (Exhibit 10.8, Registration No. 333-6795)
 
     10.9  Collaborative Research and License Agreement between the Registrant and Bristol-Myers Squibb Company and
           the Registrant, dated June 25, 1996. (Exhibit 10.9, Registration No. 333-6795)
 
    10.10  Screening Agreement, dated November 28, 1995, between the Registrant and Monsanto Company. (Exhibit
           10.11, Registration No. 333-6795)
 
    10.11  Letter Agreement, dated January 18, 1996, between Pharm-Eco Laboratories, Inc. and the Registrant.
           (Exhibit 10.12, Registration No. 333-6795)
 
   +10.12  Research Collaboration and License Agreement with ArQule, Inc., dated October 22, 1997. (Exhibit 10.12,
           Annual Report on Form 10K No., File No.)
 
    10.13  Lease Agreement between Registrant and Stimpson Family Trust dated April 30, 1993, regarding 24 Emily
           Street, Cambridge, MA., as amended by the First Amendment to Lease, dated September 19, 1994. (Exhibit
           10.13, Registration No.333-6795)
 
    10.14  Form of Employee Confidentiality and Nondisclosure Agreement. (Exhibit 10.15, Registration No. 333-6795)
</TABLE>
 
                                       63
<PAGE>
<TABLE>
<CAPTION>
EXHIBITS
- ---------
<C>        <S>
    10.15  Master Lease Agreement between the Registrant and Comdisco, Inc., dated as of August 30, 1993, as
           amended February 7, 1995, and as further amended on February 26, 1996. (Exhibit 10.16, Registration No.
           333-6795)
 
    10.16  Series B Convertible Preferred Stock Purchase Warrant between the Registrant and Comdisco, Inc., dated
           August 30, 1993. (Exhibit 10.17, Registration No. 333-6795)
 
    10.17  Series C Convertible Preferred Stock Purchase Warrants between the Registrant and Comdisco, Inc., dated
           February 28, 1995 and February 26, 1996. (Exhibit 10.18, Registration No. 333-6795)
 
    10.18  Series C Convertible Preferred Stock Purchase Options issued to Dr. Paul Schimmel and Dr. Julius Rebek
           in May 1995, as amended by certain Letter Agreements, dated October 23, 1995, between the Registrant and
           each of Dr. Schimmel and Dr. Rebek. (Exhibit 10.19, Registration No. 333-6795)
 
    10.19  Amended and Restated Stockholders Rights Agreement by and among the Registrant and the parties signatory
           thereto. (Exhibit 10.20, Registration No. 333-6795)
 
    10.20  Secured Promissory Note, dated as of July 21, 1994, by Scott M. Rocklage to the Registrant. (Exhibit
           10.21, Annual Report on Form 10-K, filed March 31, 1997, File No. 000-21379)
 
    10.21  Amendment to Promissory Note, dated as of July 21, 1996, by and between the Registrant and Scott M.
           Rocklage. (Exhibit 10.22, Annual Report on Form 10-K, filed March 31, 1997, File No. 000-21379)
 
    10.22  Amendment to Promissory Note, dated as of December 23, 1997, by and between the Registrant and Scott M.
           Rocklage. (Exhibit 10.22, Annual Report on Form 10-K, filed March 20, 1998, File No. 000-21379)
 
    10.23  Promissory Note, dated as of October 18, 1995, by and between the Registrant and Scott M. Rocklage.
           (Exhibit 10.23, Annual Report on Form 10-K, filed March 20, 1998, File No. 000-21379)
 
   +10.24  Compound Library Screening Agreement between the Registrant and Genzyme Corporation, dated February 24,
           1997. (Exhibit 10.24, Annual Report on Form 10-K, filed March 31, 1997, File No. 000-21379)
</TABLE>
 
                                       64
<PAGE>
<TABLE>
<CAPTION>
EXHIBITS
- ---------
<C>        <S>
   +10.25  Library Sample Evaluation Agreement between the Registrant and Pharmacopeia, Inc., dated as of September
           11, 1996. (Exhibit 10.25, Annual Report on Form 10-K, filed March 31, 1997, File No. 000-21379)
 
    10.26  Stock Purchase Agreement, dated July 18, 1997, between International Biotechnology Trust plc and the
           Company. (Exhibit 10.27, Registration No. 333-33883)
 
    10.27  Registration Rights Agreement, dated July 18, 1997, between International Biotechnology Trust plc and
           the Company. (Exhibit 10.28, Registration No. 333-33883)
 
    10.28  Registration Rights Agreement, dated July 18, 1997, between each of H&Q Healthcare Investors and H&Q
           Life Sciences Investors and the Company. (Exhibit 10.29, Registration No. 333-33883)
 
    10.29  Incentive Stock Option Agreement, dated as of May 19, 1997, between Mark Carthy and the Company.
           (Exhibit 10.1, Quarterly Report on Form 10-Q filed August 13, 1997, File No. 000-21379)
 
    10.30  Letter Agreement, dated as of May 19, 1997, between Mark Carthy and the Company. (Exhibit 10.2,
           Quarterly Report on Form 10-Q filed August 13, 1997, File No. 000-21379)
 
    10.31  Secured Promissory Note, dated May 19, 1997, between Mark Carthy and the Company. (Exhibit 10.3,
           Quarterly Report on Form 10-Q filed August 13, 1997, File No. 000-21379)
 
    10.32  Stock Pledge Agreement, dated May 19, 1997, between Mark Carthy and the Company. (Exhibit 10.4,
           Quarterly Report on Form 10-Q filed August 13, 1997, File No. 000-21379)
 
    10.33  Letter Agreement, dated as of January 9, 1998, by Mark Carthy and the Company. (Exhibit 10.33, Annual
           Report on Form 10-K, filed March 20, 1998, File No. 000-21379)
 
    10.34  Master Lease Agreement between the Registrant and Transamerica Business Credit, dated as of February 14,
           1997. (Exhibit 10.33, Annual Report on Form 10-K, filed March 20, 1998, File No. 000-21379)
 
   +10.35  License Agreement, dated November 7, 1997, between the Company and Eli Lilly. (Exhibit 10.3, Quarterly
           Report on Form 10-Q, filed November 14, 1997, File No. 000-21379)
 
   +10.36  Amendment No. 1 to Collaborative Research and License Agreement with Merck, dated as of October 30, 1997
           (Exhibit 10.1, Quarterly Report on Form 10-Q, filed August 12, 1998, File No. 000-21379)
</TABLE>
 
                                       65
<PAGE>
<TABLE>
<CAPTION>
EXHIBITS
- ---------
<C>        <S>
   +10.37  Amendment No. 2 to Collaborative Research and License Agreement with Merck, dated as of April 30, 1998
           (Exhibit 10.2, Quarterly Report on Form 10-Q, filed August 12, 1998, File No. 000-21379)
 
    10.38  First Amendment to Amended and Restated 1993 Stock Option Plan. (Exhibit 10.3, Quarterly Report on Form
           10-Q, filed August 12, 1998, File No. 000-21379)
 
    10.39  1997 Employee Stock Purchase Plan. (Exhibit 10.4, Quarterly Report on Form 10-Q, filed August 12, 1998,
           File No. 000-21379)
 
    10.40  Securities Purchase Agreement, dated as of September 10, 1998 between the Company and each of the
           Purchasers listed on Exhibit A thereto. (Exhibit 10.1, Quarterly Report on Form 10-Q, filed November 4,
           1998, File No. 000-21379)
 
    10.41  Registration Rights Agreement, dated as of September 10, 1998 between the Company and each person listed
           on Exhibit A thereto. (Exhibit 10.2, Quarterly Report on Form 10-Q, filed November 4, 1998, File No.
           000-21379)
 
    10.42  Common Stock Purchase Warrants, dated September 23, 1998, executed by the Company. (Exhibit 10.3,
           Quarterly Report on Form 10-Q, filed November 4, 1998, File No. 000-21379)
 
     23.1  Consent of PricewaterhouseCoopers LLP
 
           Unless otherwise indicated, all of the above-listed Exhibits are incorporated by reference from the
           Company's filing indicated.
</TABLE>
 
- ------------------------
 
+   Confidential Treatment requested: Omitted portions filed separately with the
    Commission.
 
                                       66
<PAGE>
                                   SIGNATURES
 
    Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.
 
<TABLE>
<S>                             <C>  <C>
                                CUBIST PHARMACEUTICALS, INC.
 
                                By:            /s/ SCOTT M. ROCKLAGE
                                     -----------------------------------------
                                                 Scott M. Rocklage
                                       PRESIDENT AND CHIEF EXECUTIVE OFFICER
</TABLE>
 
                                       67
<PAGE>
    Pursuant to the requirements of the Securities Exchange Act of 1934, this
report has been signed below by the following persons on its behalf of the
registration and in the capacities on the dates indicated.
 
<TABLE>
<CAPTION>
          SIGNATURE                       TITLE                    DATE
- ------------------------------  --------------------------  -------------------
 
<C>                             <S>                         <C>
 
                                President, Chief Executive
    /s/ SCOTT M. ROCKLAGE         Officer and Director
- ------------------------------    (Principal Executive           03/10/99
      Scott M. Rocklage           Officer)
 
      /s/ THOMAS A. SHEA        Treasurer (Principal
- ------------------------------    Financial and Accounting       03/10/99
        Thomas A. Shea            Officer)
 
      /s/ JOHN K. CLARKE
- ------------------------------  Chairman of the Board of         03/15/99
        John K. Clarke            Directors
 
       /s/ BARRY BLOOM
- ------------------------------  Director                         03/10/99
         Barry Bloom
 
     /s/ GEORGE CONRADES
- ------------------------------  Director                         03/10/99
       George Conrades
 
   /s/ DAVID W. MARTIN, JR.
- ------------------------------  Director                         03/13/99
     David W. Martin, Jr.
 
     /s/ PAUL R. SCHIMMEL
- ------------------------------  Director                         03/11/99
       Paul R. Schimmel
</TABLE>
 
                                       68

<PAGE>

                                                                  EXHIBIT 23.1


                        CONSENT OF INDEPENDENT ACCOUNTANTS

We consent to the incorporation by reference in the registration statements 
of Cubist Pharmaceuticals, Inc., on Forms S-3 (File nos. 333-33883 and 
333-64943) and Forms S-8 (File nos. 333-25707, 333-65385 and 333-65383) of 
our report dated February 15, 1999, on our audits of the financial statements 
of Cubist Pharmaceuticals, Inc., as of December 31, 1998 and 1997, and for 
the years ended December 31, 1998, 1997 and 1996, which report is included in 
this Annual Report on Form 10-K.


                                          /s/ PricewaterhouseCoopers LLP
                                          -------------------------------


Boston, Massachusetts
March 16, 1999



<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<CIK> 0000912183
<NAME> CUBIST PHARMACEUTICALS, INC.
       
<S>                             <C>
<PERIOD-TYPE>                   YEAR
<FISCAL-YEAR-END>                          DEC-31-1998
<PERIOD-START>                             JAN-01-1998
<PERIOD-END>                               DEC-31-1998
<CASH>                                       6,643,688
<SECURITIES>                                12,547,850
<RECEIVABLES>                                        0
<ALLOWANCES>                                         0
<INVENTORY>                                          0
<CURRENT-ASSETS>                            15,387,611
<PP&E>                                       7,727,821
<DEPRECIATION>                             (3,908,054)
<TOTAL-ASSETS>                              23,136,952
<CURRENT-LIABILITIES>                        1,742,908
<BONDS>                                              0
                                0
                                          0
<COMMON>                                        16,643
<OTHER-SE>                                  23,120,309
<TOTAL-LIABILITY-AND-EQUITY>                23,136,952
<SALES>                                              0
<TOTAL-REVENUES>                             1,634,199
<CGS>                                                0
<TOTAL-COSTS>                                        0
<OTHER-EXPENSES>                            13,984,522
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                           (333,602)
<INCOME-PRETAX>                           (11,825,006)
<INCOME-TAX>                                         0
<INCOME-CONTINUING>                       (11,825,006)
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                              (11,825,006)
<EPS-PRIMARY>                                    (.97)
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</TABLE>


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