Gilead Begins Multinational Phase III Trial of Once Daily Oral Anti-HIV Drug, Tenofovir Disoproxil Fumarate

Foster City, CA -- November 30, 1999

Gilead Sciences, Inc. (Nasdaq: GILD) announced today that it has begun enrolling patients in a multinational Phase III clinical trial of its investigational agent tenofovir disoproxil fumarate (tenofovir DF) for the treatment of human immunodeficiency virus (HIV) infection. The study is designed to enroll a total of 600 patients at nearly 70 sites in the United States, Europe and Australia. This trial is the first in a series of pivotal studies to define the role of tenofovir DF in the management of HIV disease. Tenofovir DF is a nucleotide analogue formulated as a pill taken once daily as part of combination antiretroviral regimens.

"We are very pleased to begin enrollment in the first study of a comprehensive Phase III program evaluating tenofovir DF,” said John C. Martin, Ph.D., President and Chief Executive Officer. “We recognize the challenges faced daily by physicians and patients when constructing new regimens for the treatment of people with HIV infection. With the antiviral activity and safety profile seen in early clinical trials, tenofovir DF has the potential to provide people at various stages of HIV disease with an important new treatment alternative."

Study Design

The Phase III study (GS 907) is a 48-week randomized, double-blind trial that will evaluate the safety and antiviral activity (as assessed by the Roche Amplicor® Monitor™ Ultrasensitive Test) of tenofovir DF as a component of combination antiretroviral regimens in treatment-experienced patients. The study is designed to enroll up to 600 patients infected with HIV who have HIV RNA levels greater than/equal to 400 copies/mL and less than/equal to 10,000 copies/mL and who have maintained a stable antiretroviral regimen (comprised of not more than three antiretroviral agents) for at least eight weeks prior to enrollment.

Based on preliminary efficacy and safety results from the dose ranging Phase II trial (Study 902) of tenofovir DF, patients enrolling in Study 907 will be randomized (2:1) to receive a dose of tenofovir DF 300 mg or placebo in addition to their existing regimens. Following randomization, patients will be encouraged to maintain their antiretroviral regimen for 24 weeks of blinded dosing. After 24 weeks, patients receiving tenofovir DF 300 mg may make changes in their background antiretroviral therapy and patients assigned to receive placebo will crossover to open-label active tenofovir DF for the remainder of the 48-week study period.

Phase II Preliminary Results

In September 1999, Gilead presented preliminary results from a randomized, double-blind Phase II clinical trial (Study 902) evaluating the safety and efficacy of once-daily tenofovir DF when added to a stable background antiretroviral regimen in treatment-experienced HIV patients. The 48-week dose-ranging study enrolled 189 treatment-experienced patients at 22 U.S. sites who were on a stable antiretroviral regimen for at least 8 weeks prior to entering the study. Patients were randomized to receive one of three tenofovir DF doses (300 mg, 150 mg or 75 mg) or placebo (2:2:2:1) in addition to their existing treatment regimen. At week 24, all placebo patients were switched to the tenofovir DF 300 mg treatment arm.

The primary efficacy analysis was conducted on data compiled through the 24-week placebo-controlled period. Anti-HIV activity was observed in all three active treatment arms, with the greatest reduction in viral load (-0.75 log10 copies/mL at week 24) observed in the 300 mg dosing arm. Treatment with tenofovir DF was well tolerated at all three dose levels for up to 48 weeks. The incidence of serious adverse events was similar among all study arms and was reported in 7% of patients in the 300 mg dose group compared with 11% of patients in the placebo group; drug-related nephrotoxicity was not observed. As of November 30, 1999, 77 (41 percent) of the 189 patients enrolled in Study 902 have completed 48 weeks of dosing and have rolled over into open label extended dosing.

Enrollment Information for Gilead’s Tenofovir DF Studies

To address the need for new treatment options among treatment-experienced patients, Gilead has initiated a limited compassionate access protocol for tenofovir DF (Study 908) designed to enroll up to 300 patients in the United States. Patients and physicians who would like more information about enrollment in either Study 907 or 908 of tenofovir DF for the potential treatment of HIV/AIDS may call the AIDS Clinical Trials Information System (ACTIS) at 1-800-TRIALS-A or Gilead Sciences Medical Information at 1-800-GILEAD-5 (1-800-445-3235).

Gilead Sciences

Gilead Sciences, headquartered in Foster City, CA, is an independent biopharmaceutical company that seeks to provide accelerated solutions for patients and the people who care for them. The Company discovers, develops, manufactures and commercializes proprietary therapeutics for challenging infectious diseases (viral, fungal and bacterial infections) and cancer. Gilead maintains research, development or manufacturing facilities in Foster City, CA, Boulder, CO, San Dimas, CA, and Cambridge, UK, and sales and marketing organizations in the United States, Europe and Australia.