Cubist Pharmaceuticals Announces the End of Patient Dosing in HepeX-B(TM) Hepatitis B Phase 2 Trial.

LEXINGTON, Mass. -- Plans to Review Data with the FDA 

Cubist Pharmaceuticals, Inc. (Nasdaq: CBST) today announced that Cubist and XTLbio have ended patient dosing in the second of two Phase 2 hepatitis B clinical trials of HepeX-B(TM). Cubist plans to review data from this trial with the FDA as part of a discussion of design elements of a Phase 3 trial. A Data Safety Monitoring Board recently reviewed safety data from all patients in the second Phase 2 trial and no concerns were raised.

About Hepatitis B (HBV)

Hepatitis B is most commonly caused by the Hepatitis B virus, which, according to Datamonitor, has infected over 2 billion people around the world. Although a vaccine against HBV was introduced in 1982, globally, 350 million people are infected chronically with the disease and approximately 1 million people die each year as a result of complications from HBV infection. Current treatment regimens for chronic HBV often include use of interferon alpha or an antiviral drug. Despite these treatment options, chronic HBV can lead to severe liver damage and patients may require liver transplantation To prevent re-infection of the new liver with HBV, patients are currently treated with hepatitis B immune globulin (HBIg) combined with an antiviral compound, such as lamivudine. The global market for HBIg is estimated to be about $100 million annually.

About HepeX-B(TM)

HepeX-B(TM) is a combination of two fully human monoclonal antibodies, selected using XTLbio's pre-clinical Trimera(TM) model, that target HBV surface antigens. It is currently in evaluation for the prevention of infection by HBV in liver transplant patients who have been maintained on HBIg. HepeX-B(TM) has already been granted Orphan Drug Status in both the U.S. and the European Union.

About Cubist

Cubist Pharmaceuticals, Inc. is a biopharmaceutical company focused on the research, development and commercialization of antiinfective products that address unmet medical needs in the acute care environment. In the U.S., Cubist markets CUBICIN(R) (daptomycin for injection), the first antibiotic in a new class of antiinfectives called lipopeptides. 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) in complicated skin and skin structure infections. The Company has announced that its Phase 3 Staphylococcus aureus (S. aureus) endocarditis and bacteremia trial of CUBICIN(R) (daptomycin for injection) at 6 mg/kg once daily met its primary endpoints of non-inferiority in the intent-to-treat (ITT) and per protocol (PP) populations. Cubist expects to file a supplemental New Drug Application (sNDA) before year-end 2005 seeking priority review for approval to add S. aureus endocarditis and bacteremia to the indication statement for CUBICIN. Cubist's pipeline includes HepeX-B(TM), a monoclonal antibody biologic being evaluated to determine its potential for the prevention of infection by the Hepatitis B virus (HBV) in liver transplant patients, and research efforts focused on novel members of the lipopeptide class of molecules and on natural products discovery. Cubist is headquartered in Lexington, MA.

About XTLbio

XTL Biopharmaceuticals Ltd. (XTLbio) is a biopharmaceutical company developing drugs against hepatitis. Established in 1993, XTLbio became a public company in 2000 and its ordinary shares are listed on the Official List of the UK Listing Authority and are traded on the London Stock Exchange under the symbol XTL and in the Tel Aviv Stock Exchange, Israel.

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 expectations regarding our ability to continue to manufacture sufficient quantities of CUBICIN in accordance with current Good Manufacturing Practices; (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, including HepeX-B; (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 expectations regarding the future market demand and medical need for CUBICIN; (xi) Cubist's ability to protect its intellectual property and proprietary technologies; and (xii) 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.

Cubist and CUBICIN are registered trademarks of Cubist Pharmaceuticals, Inc.; HepeX-B is a trademark of XTL Biopharmaceuticals Ltd.

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