Cubist Announces New Cidecin Data Presented At ASM Meeting.

Business Editors/Health/Medical Writers

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LEXINGTON, Mass.--(BUSINESS WIRE)--May 21, 2003

Cidecin Shown to be Rapidly Cidal in vitro Against Second VRSA Strain and Synergistic with Oxacillin in vitro; Demonstrates Efficacy in Animal Model of Endocarditis 

Cubist Pharmaceuticals, Inc. (Nasdaq: CBST) today announced presentations of new in vitro and animal data on its investigational antibiotic Cidecin(R) (daptomycin for injection). The data were presented at the 103rd General Meeting of the American Society for Microbiology (ASM), taking place in Washington, DC, May 17 through May 21, 2003. The CIDECIN New Drug Application is currently being reviewed by the U.S. Food & Drug Administration under priority review status.

The first isolate of Staphylococcus aureus to be fully resistant to the drug vancomycin was reported by the Centers for Disease Control and Prevention (CDC) in July 2002. Data previously presented in September 2002 demonstrated daptomycin to be the most rapidly bactericidal (killing) of all agents studied against this strain in vitro. A second isolate of vancomycin-resistant S. aureus (VRSA) was reported in September 2002. In Poster #A-075, Drs. P. C. Appelbaum of Penn State Hershey Medical Center, Hershey, PA, and F. C. Tenover of the CDC, Atlanta, GA, presented in vitro data comparing the activity of commercially available drugs, including linezolid, quinupristin/dalfopristin and trimethoprim/sufamethoxazole, to the activity of experimental agents, including daptomycin, oritavancin and tigecycline, against this second multi-drug resistant VRSA isolate. In this study, bactericidal activity was defined as the lowest concentration at which the agent reduced the original inoculum by at least 3 log10 colony forming units (cfu)/mL at each time point. Daptomycin was the only agent studied that demonstrated bactericidal activity at the 3-hour time point at one times its minimum inhibitory concentration (MIC).

The results of another in vitro study were presented by Dr. K. H. Rand of the Department of Pathology at the University of Florida, Gainesville, FL in Poster #C-091. Following his previous study demonstrating that daptomycin had marked synergistic in vitro activity when used in combination with rifampin and ampicillin against vancomycin-resistant enterococci (VRE), Dr. Rand designed this study to look for synergy between daptomycin and the semi-synthetic penicillin oxacillin against 18 strains of methicillin-resistant S. aureus (MRSA) in vitro. At concentrations well below daptomycin's MIC against MRSA, bactericidal synergy was observed in 18/18 (100%) MRSA strains at one half daptomycin MIC, and even in 11/18 (61%) at one quarter daptomycin MIC. The poster concluded that "the uniformity of both bactericidal activity and synergy make the combination of daptomycin and oxacillin . . . very promising for the treatment of MRSA, but further studies are needed to elucidate the mechanisms and determine in vivo efficacy."

In Poster #A-025, Cubist scientists reported results on the efficacy of daptomycin in a rodent fibrin clot model of endocarditis caused by MRSA. This study examined the efficacy of daptomycin, vancomycin and linezolid against MRSA in subcutaneous fibrinogen and thrombin clots, similar to the fibrous vegetations seen in human endocarditis. Results demonstrated that daptomycin effectively penetrated the clots containing MRSA and that both vancomycin and linezolid were less effective than daptomycin in killing MRSA in this endocarditis model in rodents. Cubist is currently investigating the safety and efficacy of CIDECIN in the treatment of endocarditis caused by S. aureus in an ongoing Phase 3 clinical trial.

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 being reviewed by 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