Gilead Announces the Advancement of HIV Integrase Inhibitor GS 9137 to a Phase II Clinical Trial

FOSTER CITY, Calif.--(BUSINESS WIRE)--Jan. 9, 2006--Gilead Sciences, Inc. (Nasdaq:GILD) today announced that it has completed a Phase I/II study of JTK-303, or GS 9137, an oral HIV integrase inhibitor for the treatment of HIV licensed from Japan Tobacco (JT) in March 2005. The company anticipates presenting results from the Phase I/II dose-escalation study, which evaluated the tolerability, safety and antiviral activity of GS 9137 in HIV-positive patients, at an upcoming scientific conference. Based on the results of this study, Gilead anticipates evaluating three once-daily doses for GS 9137, 20 mg, 50 mg and 125 mg, each boosted with ritonavir 100 mg in a Phase II clinical trial, which it plans to initiate in the first half of this year.

"The development of therapies targeting new steps of the HIV lifecycle such as integrase is critical, particularly for treatment-experienced patients with limited options," said Norbert Bischofberger, PhD, Executive Vice President, Research and Development, Gilead Sciences. "We are encouraged by the significant viral load reduction observed in HIV-infected patients in the Phase I/II study in which the 50 mg dose, in combination with ritonavir as a boosting agent, showed antiviral activity similar to the most potent protease inhibitors. We are working quickly to finalize the protocol design so that we may initiate larger Phase II and Phase III studies."

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 will retain rights. GS 9137 has been previously evaluated in a Phase I study in Japan to assess pharmacokinetics and safety in healthy volunteers.

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 develop and commercialize this product. For example, the safety and efficacy data from this trial may not warrant further development of this compound and initiating and completing clinical trials may take longer or cost more than expected. 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 Annual Report on Form 10-K for the year ended December 31, 2004, 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 web site 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.