Gilead Sciences Presents Clinical Data Demonstrating Activity of PREVEON in Patients With 3TC and AZT Resistant HIV.

FOSTER CITY, Calif.--(BW HealthWire)--June 25, 1998--Gilead Sciences (NASDAQ:GILD) announced today the presentation of clinical data demonstrating the anti-HIV activity of PREVEON(TM) (adefovir dipivoxil), an experimental reverse transcriptase inhibitor, in patients who have developed resistance mutations associated with the commonly used antiretroviral agents AZT (zidovudine) and 3TC (lamivudine).

These placebo-controlled data, collected from 142 patients enrolled in a Phase II/III clinical trial (Study 408), also demonstrate that once-daily treatment with PREVEON for 24 weeks was not associated with the emergence of the adefovir-associated resistance mutations (K65R or K70E) identified in vitro.

These data were presented this week at the "Second International Workshop on HIV Drug Resistance and Treatment Strategies" in Lake Maggiore, Italy by Julie Cherrington, Ph.D., Director of Virology at Gilead Sciences.

The mutation associated with the use of 3TC (M184V) was detected in a majority of patients (76%) at study entry. In the PREVEON treatment group, a mean HIV RNA change of -0.94 log10 was observed at 24 weeks in patients with the 3TC mutation alone; -0.75 log10 in patients with the 3TC mutation and low-level AZT resistance; and -0.51 log10 in patients with the 3TC mutation and high-level AZT resistance. These results compare to +0.09 log10, +0.07 log10 and -0.04 log10, respectively, in placebo patients with the same resistance patterns. In patients who had high-level AZT resistant mutations alone without the M184V mutation present at baseline, PREVEON was not associated with a decrease in HIV RNA.

As previously reported, data from all patients enrolled in Study 408 (n=442) demonstrate a statistically significant mean reduction in HIV RNA of -0.39 log10 after 24 weeks in patients assigned to the PREVEON group versus a -0.01 log10 decrease in patients assigned to the placebo group (p<0.0001).

Study Design and Background Information

In this study, HIV treatment-experienced patients were randomized to receive 24 weeks of PREVEON (120 mg tablet) or placebo once per day in combination with other approved anti-HIV therapies, including protease inhibitors. On average, patients had received treatment with three nucleoside reverse transcriptase inhibitors and three years of AZT treatment at the time of study enrollment. The mean HIV RNA at baseline was 4.4 log10.

To date, more than 5,000 patients have received PREVEON through clinical trials for the potential treatment of HIV, including more than 3,200 patients who have enrolled in the U.S. expanded access program for patients with limited treatment options.

In these clinical trials, treatment with PREVEON has been associated with decreases in HIV RNA (a marker of viral infection) and increases in CD4 cell counts (a measure of immune function). Side effects observed include changes in laboratory markers of renal function, dose-related gastrointestinal effects, including nausea and loss of appetite, weight loss and elevations in liver transaminases. Changes in laboratory markers of renal function, including increases in serum creatinine, have been observed in up to one-third of patients receiving PREVEON for 48 weeks. More detailed safety and activity data from Study 408 will be presented during a Satellite Symposium at the 12th World AIDS Conference in Geneva, Switzerland on Wednesday, July 1.

Gilead Sciences is an independent biopharmaceutical company that seeks to provide accelerated treatment solutions for patients and the people who care for them. The Company discovers, develops and commercializes proprietary therapeutics for the important viral diseases, including a currently marketed product, VISTIDE(R) (cidofovir injection), for the treatment of CMV retinitis, a sight-threatening viral infection in patients with AIDS. In addition, the Company is developing products to treat diseases caused by HIV, hepatitis B virus and influenza virus. Gilead common stock is traded on The Nasdaq Stock Market under the symbol GILD.

PREVEON is a trademark and VISTIDE is a registered trademark of Gilead Sciences, Inc.

For more information or to receive a copy of the scientific abstract summarizing these findings, please contact Gilead's Corporate Communications and Investor Relations Department at 1-800-GILEAD-5 (1-800-445-3235) or visit our Website: www.gilead.com.

Note to Editors: "log10" is properly written with the "10" sub-script.

CONTACT: Gilead Sciences

Lana Lauher (Investors), 650/573-4858

Laurie Hurley (Media), 650/573-4894