Cubist Pharmaceuticals Presents First Human Data on Investigational Antibiotic CAB-175; Data Presented at 13th ECCMID Meeting in Glasgow.

Business Editors/Health/Medical Writers

BIOWIRE2K

GLASGOW, Scotland & LEXINGTON, Mass.--(BUSINESS WIRE)--May 13, 2003

Cubist Pharmaceuticals, Inc. (Nasdaq: CBST) today presented the first human data on its investigational cephalosporin antibiotic CAB-175 at the 13th European Congress on Clinical Microbiology and Infectious Diseases (ECCMID) being held May 10 through May 13, 2003 in Glasgow, Scotland.

Poster #P792 provided detailed results of a Phase 1 study, conducted in the United Kingdom, designed to assess the safety, tolerability and pharmacokinetic (PK) profile of a single intravenous dose of CAB-175 at dose levels of 250 mg, 500 mg and 1000 mg in healthy male subjects. Overall results of the study indicated that a single dose of CAB-175 up to 1000 mg was tolerated by normal, healthy male subjects, and that initial safety and PK results from this study suggest that further clinical evaluation of CAB-175 is warranted. In the study, there were no serious adverse events reported and no subjects discontinued due to an adverse event. The PK results from the study suggested that twice-daily intravenous dosing of the compound may be appropriate in further human clinical studies.

In an oral session today, Cubist for the first time presented an overview of completed animal studies on CAB-175. The data presented demonstrated therapeutic efficacy of CAB-175 in a model of pulmonary infection caused by Streptococcus pneumoniae, and against methicillin-resistant Staphylococcus aureus (MRSA) infection in both fibrin clot and thigh tissue models meant to simulate endocardial vegetations (endocarditis) and deep-seated skin and skin structure infections, respectively.

In addition to the human and animal data, multiple posters were presented detailing the microbiologic profile of CAB-175. Most notably, data presented in Poster #P793 indicate that CAB-175 displays potent bactericidal in vitro activity against MRSA, as well as broad-spectrum bactericidal activity against clinically important Gram-negative and Gram-positive bacteria.

About CAB-175

CAB-175 is a novel investigational cephalosporin antibiotic that has demonstrated in vitro activity against most clinically relevant Gram-positive and Gram-negative bacteria, including 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 35% of S. aureus hospital-acquired infections in the U.S. and up to 42% and 70% of similar infections in parts of Europe and Asia, respectively. In in vitro studies, CAB-175 has thus far demonstrated a very low potential for the development of bacterial resistance.

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) with the U.S. Food & Drug Administration (FDA) for Cidecin(R) (daptomycin for injection) for the treatment of complicated skin and skin structure infections (cSSSI) and is conducting additional Phase 3 studies. The CIDECIN NDA is currently under review at FDA under priority review status. Cubist's pipeline includes multiple pre-clinical drug candidates, including CAB-175, a next generation cephalosporin antibiotic with demonstrated in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA) and an oral version of ceftriaxone (OCTX), a broad-spectrum cephalosporin antibiotic. 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(R) is a registered trademark of Cubist Pharmaceuticals, Inc.

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