Cubist Pharmaceuticals Announces Completion of Second Safety Review of Endocarditis/Bacteremia Data for Cubicin by DMC; DMC Again Recommends Continuation of Trial.

Business Editors/Health/Medical Writers

BIOWIRE2K

LEXINGTON, Mass.--(BUSINESS WIRE)--April 1, 2004

Cubist Pharmaceuticals, Inc. (Nasdaq: CBST) today announced the completion of the second planned safety review of patients enrolled in Cubist's ongoing international Phase 3 clinical trial examining the safety and efficacy of Cubicin(TM) (daptomycin for injection) in the treatment of infective endocarditis and bacteremia caused by Staphylococcus aureus.

Due to the high mortality rate associated with endocarditis, blinded clinical data from patients enrolled in the study are provided to an independent data monitoring committee (DMC) at pre-determined intervals to identify any safety-related issues. Based upon this second review of the data, the DMC has recommended continuation of the trial.

Patients with blood cultures positive for the presence S. aureus are currently being enrolled at sites in the U.S. and certain Western European countries. In the study, patients receive either CUBICIN at 6 mg/kg once daily or the current standards of care, vancomycin in patients with confirmed methicillin-resistant S. aureus (MRSA) infection or a semi-synthetic penicillin if susceptible S. aureus is confirmed. This is the first Phase 3 trial to be conducted for the indication of endocarditis in almost 20 years. Cubist continues to expect data from the trial to be available in the first half of 2005.

On Cubicin(TM) (daptomycin for injection)

To reduce the development of drug-resistant bacteria and maintain the effectiveness of CUBICIN, CUBICIN should be used only to treat or prevent infections that are proven or strongly suspected to be caused by bacteria susceptible to CUBICIN. For full prescribing information, visit www.Cubicin.com.

About Cubist

Cubist Pharmaceuticals, Inc. is a biopharmaceutical company focused on the research, development and commercialization of drugs that meet significant unmet medical needs. Since its founding in 1992, Cubist has been exclusively focused on exploiting business and product opportunities in the antiinfective marketplace. In the U.S., Cubist markets Cubicin(TM) (daptomycin for injection), the first antibiotic in a new class of antiinfectives called lipopeptides, for the indication of complicated skin and skin structure infections caused by Gram-positive bacteria. Cubicin(TM) is currently the only once-daily bactericidal antibiotic approved in the U.S. with activity against both methicillin-susceptible and methicillin-resistant Staphylococcus aureus (MSSA and MRSA). Cubist's pre-clinical pipeline includes an oral version of ceftriaxone (OCTX), a broad-spectrum cephalosporin antibiotic, and other novel members of the lipopeptide class. Cubist is headquartered in Lexington, MA.

Cubist Safe Harbor Statement

Statements contained herein that are not historical fact may be 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, and such statements are subject to a variety of risks and uncertainties. There are a number of important factors that could cause actual results to differ materially from those projected or suggested in any forward-looking statements made by Cubist. These factors include, but are not limited to: (i) the level of acceptance of CUBICIN by physicians, patients, third-party payors, and the medical community generally; (ii) Cubist's ability to continue to develop, secure additional regulatory approvals for, and successfully market, CUBICIN; (iii) Cubist's ability to manufacture CUBICIN on a commercial scale; (iv) commercialization of products that are competitive with CUBICIN; (v) Cubist's ability to discover or in-license drug candidates; (vi) Cubist's ability to successfully develop drug candidates in its pipeline; (vii) Cubist's ability to successfully commercialize any product or technology developed by Cubist; (viii) Cubist's ability to establish and maintain successful manufacturing, sales and marketing, distribution, and development collaborations; (ix) legislative or regulatory changes adversely affecting Cubist or the biopharmaceutical industry; (x) Cubist's ability to protect its intellectual property and proprietary technologies; and (xi) Cubist's ability to finance its operations. Additional factors that could cause actual results to differ materially from those projected or suggested in any forward-looking statements are contained in Cubist's recent filings with the Securities and Exchange Commission, including those factors discussed under the caption "Risk Factors" in such filings.

Cubicin is a trademark of Cubist Pharmaceuticals, Inc.

Additional information can be found at Cubist's web site at www.cubist.com.