Phase II Clinical Trial of Gilead's Investigational
Integrase-Based, Once-Daily, Fixed-Dose
"Quad" Regimen Meets 24-Week Primary Objective

Foster City, Calif., January 6, 2009 -- Business Wire -- Gilead Sciences, Inc. (Nasdaq: GILD) today announced that a Phase II clinical trial of its investigational integrase inhibitor-based, once-daily, fixed-dose "Quad" regimen of elvitegravir, GS 9350 and Truvada (emtricitabine and tenofovir disoproxil fumarate) for the treatment of HIV-1 infection met its primary objective. The ongoing study of 71 HIV-infected, antiretroviral treatment-naive adults compares the Quad with Atripla (efavirenz 600 mg/emtricitabine 200 mg/tenofovir disoproxil fumarate 300 mg). Based on 24-week data, efficacy of the Quad met the statistical criteria of non-inferiority as compared to Atripla based on the proportion of subjects with HIV RNA levels (viral load) of less than 50 copies/mL. Discontinuation rates due to adverse events were comparable in both arms of the study. Full study results will be submitted for presentation at a scientific meeting in early 2010.

Elvitegravir is Gilead's investigational HIV integrase inhibitor. GS 9350 is Gilead's investigational pharmacoenhancing or "boosting" agent, being developed to increase blood levels of certain medicines, including elvitegravir, and allows for once-daily dosing.

Gilead is also studying GS 9350 as a stand-alone boosting agent for other antiretrovirals, in particular, protease inhibitors. A Phase II clinical trial evaluating the safety and efficacy of GS 9350-boosted atazanavir compared to ritonavir-boosted atazanavir, each in combination with Truvada, is ongoing. The Phase II study involves 79 HIV-infected, antiretroviral treatment-naive adults. The study met its primary objective of achieving HIV RNA levels (viral load) of less than 50 copies/mL at 24 weeks of treatment. GS 9350-boosted atazanavir and Truvada had similar efficacy to ritonavir-boosted atazanavir and Truvada. Discontinuation rates due to adverse events were comparable in both arms of the study. Ritonavir is currently the only agent used to boost HIV therapy. Results from this study will also be submitted for presentation at a scientific meeting in early 2010.

About the Quad Phase II Study

The Quad Phase II study is a double-blind, multicenter, randomized, active-controlled 48-week clinical trial evaluating the safety and efficacy of a fixed-dose regimen containing elvitegravir, GS 9350 and Truvada versus Atripla, each administered in HIV-infected treatment-naive adults with HIV RNA levels (viral load) greater than or equal to 5,000 copies/mL and CD4 cell counts greater than 50 cells/mm3 (n=71). Entry criteria required that patients did not have nucleoside reverse transcriptase inhibitor, non-nucleoside reverse transcriptase inhibitor or primary protease inhibitor resistance mutations, as defined by International AIDS Society-USA guidelines, and no prior use of antiretroviral treatments.

In the study, trial participants were randomized 2:1 to receive a once-daily tablet containing elvitegravir 150 mg/GS 9350 150 mg/emtricitabine 200 mg/tenofovir disoproxil fumarate 300 mg (n=48) or Atripla (efavirenz 600 mg/emtricitabine 200 mg/tenofovir disoproxil fumarate 300 mg) (n=23).
The study is ongoing. Secondary endpoints will include the proportion of patients with HIV RNA levels (viral load) less than 50 copies/mL at 48 weeks of treatment, and the safety and tolerability of the two treatment regimens through 48 weeks of treatment. After week 48, subjects will continue to take blinded study drug until treatment assignments have been unblinded, at which point all subjects will be given the option to participate in an open-label rollover extension and receive the single-tablet regimen containing elvitegravir, GS 9350 and Truvada.

Additional information about the study can be found at www.clinicaltrials.gov.

About the GS 9350 Phase II Study

The GS 9350 Phase II study is a double-blind, multicenter, randomized (2:1), active-controlled 48-week clinical trial evaluating the safety and efficacy of GS 9350-boosted atazanavir (n=50) compared to ritonavir-boosted atazanavir (n=29), each in combination with Truvada, in HIV-infected treatment-naive adults with HIV RNA levels (viral load) greater than or equal to 5,000 copies/mL and CD4 cell counts greater than 50 cells/mm3. Entry criteria required that patients did not have nucleoside reverse transcriptase inhibitor, non-nucleoside reverse transcriptase inhibitor or primary protease inhibitor resistance mutations, as defined by International AIDS Society-USA guidelines, and no prior use of antiretroviral treatments.

The study is ongoing. Secondary endpoints will include the proportion of patients with HIV RNA levels (viral load) less than 50 copies/mL at 48 weeks of treatment, and the safety and tolerability of the two treatment regimens through 48 weeks of treatment. After week 48, subjects will continue to take blinded study drug until treatment assignments have been unblinded, at which point all subjects will be given the option to participate in an open-label rollover extension and receive GS 9350-boosted atazanavir and Truvada.

Additional information about the study can be found at www.clinicaltrials.gov.

About Elvitegravir

Elvitegravir is an HIV integrase inhibitor. Unlike other classes of antiretroviral agents, integrase inhibitors interfere with HIV replication by blocking the ability of the virus to integrate into the genetic material of human cells. Elvitegravir, also known as GS 9137 or JTK 303, was licensed by Gilead from Japan Tobacco Inc. (JT) in March 2005. Under the terms of Gilead's agreement with JT, Gilead has exclusive rights to develop and commercialize elvitegravir in all countries of the world, excluding Japan, where JT retains rights. Elvitegravir is an investigational compound and has not yet been determined safe or efficacious in humans.

About GS 9350

GS 9350 is Gilead's proprietary potent mechanism-based inhibitor of cytochrome P450 3A (CYP3A), an enzyme that metabolizes drugs in the body. In addition to studying the agent as part of an integrase-based fixed-dose regimen, Gilead is also examining GS 9350's potential stand-alone role in boosting commercially available HIV protease inhibitors, which are used in many HIV treatment regimens. GS 9350 is an investigational therapy and has not yet been determined safe or efficacious in humans.

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.