Cubist Pharmaceuticals Commences Phase 1 CAB-175 Trial in U.S. Following IND Filing.

Business Editors/Health/Medical Writers

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LEXINGTON, Mass.--(BUSINESS WIRE)--June 24, 2003

Cubist Pharmaceuticals, Inc. (Nasdaq: CBST) today announced that it has commenced a multi-dose Phase 1 trial in the U.S. for its investigational antibiotic CAB-175 following the filing of an Investigational New Drug (IND) application with the U.S. Food & Drug Administration (FDA).

CAB-175 is a novel parenteral cephalosporin antibiotic that has demonstrated in vitro activity against most clinically relevant Gram-positive and Gram-negative bacteria, including clinically important resistant species. If successfully developed, CAB-175 could be one of the first cephalosporin antibiotics with activity against methicillin-resistant Staphylococcus aureus (MRSA) strains, which are estimated to be the cause of more than 40% of hospital-acquired S. aureus infections in the U.S. and up to 42% and 70% of similar infections in parts of Europe and Asia, respectively.

Cubist expects to investigate CAB-175 as a treatment for a variety of clinical indications, should the Phase 1 studies be successfully completed. Preliminary supportive Phase 1 studies are designed to characterize the safety and pharmacokinetic (PK) profiles of CAB-175 in anticipation of Phase 2 studies.

Michael W. Bonney, President & CEO of Cubist commented: "With the anticipated launch of our lead investigational antibiotic Cidecin(R) (daptomycin for injection) later this year, pending FDA approval, we recognize the need to fill out our product pipeline. CAB-175 fits this need nicely and, if successfully developed, should complement CIDECIN and allow us to leverage our commercial infrastructure. Throughout the development of the compound," Mr. Bonney continued, "we are looking forward to working closely with the FDA and participating in its pilot target package insert program called TPI." The TPI (Targeted Product Information) program has been launched by the FDA, in conjunction with the Pharmaceutical Research Manufacturers Association (PhRMA), to guide the design, conduct, and analysis of clinical trials, to facilitate communication between the FDA and pharmaceutical companies, and to promote a shared understanding of a sponsor's drug development program.

About Cubist

Cubist Pharmaceuticals, Inc. is focused on becoming a global leader in the research, development and commercialization of novel pharmaceuticals to combat serious and life-threatening infections. Cubist has submitted a New Drug Application (NDA) to the U.S. Food & Drug Administration (FDA) for Cidecin(R) (daptomycin for injection) for the treatment of complicated skin and skin structure infections (cSSSI). The CIDECIN NDA is currently being reviewed by FDA under priority review status. Cubist's pipeline includes CAB-175, a next generation parenteral cephalosporin antibiotic in Phase 1 trials, and an oral version of ceftriaxone (OCTX), a broad-spectrum cephalosporin antibiotic in pre-clinical development. Cubist is headquartered in Lexington, MA.

Cubist Safeharbor 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, that 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 the Company. These factors include, but are not limited to: (i) the Company's ability to successfully complete product research and development, including pre-clinical and clinical studies and commercialization; (ii) the Company's ability to obtain required governmental approvals; (iii) the Company's ability to attract and/or maintain manufacturing, sales, distribution and marketing partners; (iv) the Company's ability to develop and commercialize its products before its competitors; and (v) the Company's ability to finance its operations. Additional factors that would cause actual results to differ materially from those projected or suggested in any forward-looking statements are contained in the Company's filings with the Securities and Exchange Commission, including those factors discussed under the caption "Risk Factors" in the Company's recent SEC filings.

Cidecin is a registered trademark of Cubist Pharmaceuticals, Inc.

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