Cubist Pharmaceuticals Announces Development Decision On OCTX Program.

Business Editors/Health/Medical Writers

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LEXINGTON, Mass.--(BUSINESS WIRE)--April 29, 2004

Company to Discontinue Investment in Program

Cubist Pharmaceuticals, Inc. (Nasdaq: CBST) today announced that results from human clinical research studies examining the bioavailability of a variety of oral formulations of ceftriaxone, a broad-spectrum antibiotic, were too variable to confirm therapeutic application of the formulations and did not meet the established threshold of bioavailability. As a result, Cubist will discontinue internal investment in the ceftriaxone formulations, known collectively as OCTX.

Michael W. Bonney, President & CEO of Cubist commented on the news: "While we are certainly disappointed that we will not be advancing OCTX into the clinic, we continue to believe that this technology platform could ultimately result in a commercial product. Over the past several years, our pharmaceutical sciences team has made important advances in increasing the oral bioavailability of an extremely difficult-to-absorb compound. We believe that the efforts made by Cubist on these formulations have added significant value to the program and are hopeful that we will be able to realize a return on our investment in the future. In the meantime, we have decided that our resources are better spent optimizing the launch of our flagship product Cubicin(TM) (daptomycin for injection) and pursuing potential in-licensing candidates to strengthen our near-term product pipeline."

Cubist originally licensed the technology from International Health Management Associates, Inc. (IHMA) and The University of Utah in late 2000. In early 2002, Cubist announced the successful completion of studies demonstrating clinically relevant blood levels of ceftriaxone delivered intraduodenally, or directly to the small intestine, in human volunteers. These studies confirmed earlier work performed in both non-human primates and rodents. Since achievement of these results, Cubist scientists have worked to optimize oral dosage formulations, achieving significantly improved bioavailability in animal and humans, but insufficient levels to justify further development and investment by Cubist.

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 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 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 further identify, develop, and achieve commercial success for new products and technologies; (vi) Cubist's ability to establish and maintain successful manufacturing, sales and marketing, distribution, and development collaborations; (vii) legislative or regulatory changes adversely affecting Cubist or the biopharmaceutical industry; (viii) Cubist's ability to protect its intellectual property and proprietary technologies; and (ix) 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