Gilead Announces Completion of Phase II Clinical Trial of Novel Investigational HIV Integrase Inhibitor GS 9137

Study Meets Primary Endpoint of Non-inferiority

FOSTER CITY, Calif.--(BUSINESS WIRE)--Feb. 23, 2007--Gilead Sciences, Inc. (Nasdaq:GILD) today announced the completion of a Phase II clinical trial of GS 9137, a novel oral HIV integrase inhibitor. The clinical study met its primary endpoint of non-inferiority in viral load reduction in HIV-positive patients receiving 50 mg or 125 mg of GS 9137 once daily, each boosted with 100 mg of ritonavir, in combination with an optimized background antiretroviral regimen compared to a boosted comparator protease inhibitor regimen (p=0.02 for the 125 mg arm).

This ongoing Phase II study is a partially-blinded, randomized, active-controlled, 48-week clinical trial to evaluate the non-inferiority of once-daily GS 9137 versus boosted comparator protease inhibitors (CPI/r) in highly treatment-experienced HIV-infected patients. After week eight, the GS 9137 20 mg arm was closed due to a high rate of virologic failure. At this time, the addition of darunavir or tipranavir to the GS 9137 study arms was permitted, following the availability of data demonstrating a lack of drug interactions between both protease inhibitors and GS 9137. The primary endpoint of the study was DAVG24, a measure of viral load reduction over 24 weeks.

Integrase inhibitors are an investigational class of antiretrovirals that interfere with HIV replication by blocking the ability of the virus to integrate into the genetic material of human cells. Novel classes of HIV-fighting drugs are needed as patients live longer and exhaust currently available treatment options.

About GS 9137

GS 9137, also known as JTK-303, was licensed by Gilead from Japan Tobacco Inc. (JT) in March 2005. Under the terms of the company's agreement with JT, Gilead has exclusive rights to develop and commercialize GS 9137 in all countries of the world, excluding Japan where JT retains rights. As an investigational compound, GS 9137 has not yet been determined safe or efficacious in humans for its ultimate intended use.

About Gilead Sciences

Gilead Sciences is a biopharmaceutical company that discovers, develops and commercializes innovative therapeutics in areas of unmet medical need. The company's mission is to advance the care of patients suffering from life-threatening diseases worldwide. Headquartered in Foster City, California, Gilead has operations in North America, Europe and Australia.

This press release includes forward-looking statements, within the meaning of the Private Securities Litigation Reform Act of 1995, that are subject to risks, uncertainties and other factors, including risks related to Gilead's ability to successfully develop and commercialize GS 9137. For example, the safety and efficacy data from additional clinical studies may not warrant further development of this compound, and initiating and completing clinical trials may take longer or cost more than expected. Future discussions with the FDA may impact the amount of data needed and timelines for review, and Gilead's clinical trial protocol design, clinical endpoint and statistical analyses for any additional trials will be subject to FDA review and approval. In addition, integrase inhibitors represent a relatively new class of compounds that has not had a long history of clinical research and development. Therefore, Gilead may face challenges in clinical trial protocol design and trial enrollment, and the results of clinical trials involving integrase inhibitors may be less predictable than with other drug candidates for the treatment of HIV. These risks, uncertainties and other factors could cause actual results to differ materially from those referred to in the forward-looking statements. The reader is cautioned not to rely on these forward-looking statements. These and other risks are described in detail in the Gilead's Annual Report on Form 10-K for the year ended December 31, 2005 and Reports on Form 10-Q for the first three quarters of 2006, filed with the U.S. Securities and Exchange Commission. All forward-looking statements are based on information currently available to Gilead, and Gilead assumes no obligation to update any such forward-looking statements.

For more information on Gilead Sciences, please visit the company's website at www.gilead.com or call Gilead Public Affairs at 1-800-GILEAD-5 or 1-650-574-3000.

CONTACT: Gilead Sciences, Inc. Susan Hubbard, 650-522-5715 (Investors) James Loduca, 650-522-5908 (Media) SOURCE: Gilead Sciences, Inc.