Preliminary 24-Week Data Evaluating the Impact of Switching from Twice-Daily Combivir(R) to Once-Daily Truvada(R) in Patients with HIV Presented at 10th European AIDS Conference

Gilead Sciences, Inc. (Nasdaq:GILD) today announced thepresentation of preliminary 24-week data from the COMET (Combinationof Efavirenz and Truvada) study at the 10th European AIDS Conference(EACS), November 17-20, 2005 in Dublin, Ireland. Data suggest that inHIV-infected treatment-experienced patients who switched fromtwice-daily Combivir(R) (lamivudine 150 mg/zidovudine 300 mg) toonce-daily Truvada(R) (emtricitabine and tenofovir disoproxilfumarate), both in combination with efavirenz, the percentage ofpatients that achieved virologic suppression below 50 copies/mL wassignificantly higher at week 24 compared to baseline. Hemoglobinlevels also increased significantly from baseline. Data will bepresented (Poster #PE7.3/5) by study investigator Peter Ruane, MD ofLifesource Medical Inc. in Los Angeles, California.

"The simplicity, tolerability and virologic benefit provided by afixed-dose combination backbone are important considerations inhelping promote long-term positive clinical outcomes," said NorbertBischofberger, PhD, Executive Vice President, Research andDevelopment, Gilead Sciences. "These data suggest that switchingvirologically suppressed patients from Combivir to Truvada may be avaluable treatment strategy for physicians and patients who areseeking to further simplify a regimen or address side effects observedwith other therapies."

Study Results

The COMET study is a U.S.-based, single-arm, multi-center 24-weekPhase IV clinical trial evaluating the impact of switchingvirologically suppressed HIV-infected treatment-experienced patientsfrom a regimen of twice-daily Combivir and once-daily efavirenz to asimplified once-daily regimen of Truvada and efavirenz. Enrollment inthe COMET study was completed in August 2005 with 411 patientsenrolled in the study. At study entry, all patients were to havereceived Combivir for at least eight weeks and have a viral load lessthan 400 copies/mL. Study endpoints include viral suppression lessthan 400 and 50 copies/mL, change in CD4 cell count, changes inpatients' hemoglobin levels and lipid profile and responses to aquestionnaire evaluating symptoms, adherence and treatmentsatisfaction (SATS).

Of the 411 total enrolled patients, 198 reached week 24 at thetime of this analysis. Nineteen patients discontinued the study priorto week 24, of which six withdrew due to adverse events, two forpregnancy, five for protocol violation or noncompliance and six werelost to follow up, withdrew consent or withdrew for other reasons.Baseline characteristics were assessed on 217 patients, who eitherreached week 24 (n=198) or withdrew early from the study (n=19). Ofthese 217 patients, 86 percent were male, 71 percent were white, 22percent were black and the median age was 42 years. Eighty-ninepercent of patients had taken Combivir for longer than one year andthe median duration of prior Combivir use (or use of its componentdrugs) was four years. Eighty-six percent of patients switched toTruvada for regimen simplification, 6 percent of patients switchedbecause of Combivir-related adverse events and 8 percent of patientscited both regimen simplification and Combivir-related adverse eventsas reasons for switching.

Based on analysis of all available 24 week data, 76 percent ofpatients had viral load of less than 50 copies/mL compared to 59percent at baseline (n=189; p less than 0.001). Ninety-four percent ofpatients maintained viral load of less than 400 copies/mL (n=189).Hemoglobin increased significantly from baseline (median +0.6 g/dL;n=191; p less than 0.001) with 32 percent of patients experiencing atleast 1 g/dL increase in hemoglobin. The most common adverse eventsobserved were nausea, diarrhea and headache. Of the 172 patients whocompleted a SATS questionnaire, a significantly greater percentage ofpatients reported being very satisfied with the treatment regimen at24 weeks (85 percent) compared to baseline (58 percent; p less than0.001).

Data from the COMET study have not been reviewed by the UnitedStates Food and Drug Administration (FDA). Changes in body fat havebeen observed in patients taking anti-HIV medicines, including thecomponent drugs of Truvada. The cause and long-term health effect ofthis condition is unknown. For the detailed indication and importantsafety information from the U.S. prescribing information for Truvada,see below.

The parent compound of one of the component drugs in Truvada,tenofovir disoproxil fumarate, was discovered through a collaborativeresearch effort between Dr. Antonin Holy, Institute for OrganicChemistry and Biochemistry, Academy of Sciences of the Czech Republic(IOCB) in Prague and Dr. Erik DeClercq, Rega Institute for MedicalResearch, Katholic University in Leuven, Belgium. The inventors haveagreed to waive their right to a royalty on sales of productscontaining tenofovir in the developing countries served by the GileadAccess Program to ensure the product can be offered at a no-profitprice in parts of the world where the AIDS epidemic has hit thehardest.

It is important that patients be aware that individual HIVmedications must be taken as part of combination regimens, and thatthey do not cure HIV infection or prevent passing HIV to others.

About Truvada

Truvada combines Emtriva(R) (emtricitabine) and Viread(R)(tenofovir disoproxil fumarate) in one tablet taken once a day incombination with other antiretroviral agents. In the United States,Truvada is indicated in combination with other antiretroviral agents(such as non-nucleoside reverse transcriptase inhibitors or proteaseinhibitors) for the treatment of HIV-1 infection in adults. Safety andefficacy studies using Truvada tablets or using Emtriva and Viread incombination are ongoing.

Emtriva and Viread have each been studied as part of multi-drugregimens and have been found to be safe and effective. In clinicalstudy 303, Emtriva and lamivudine (3TC) demonstrated comparableefficacy, safety and resistance patterns as part of multidrugregimens. These data, and those from study 903, in which lamivudineand tenofovir were used in combination, support the use of Truvada forthe treatment of HIV-1 infection in treatment-naive adults. Intreatment-experienced patients, the use of Truvada should be guided bylaboratory testing and treatment history.

Lactic acidosis and severe hepatomegaly with steatosis, includingfatal cases, have been reported with the use of nucleoside analoguesalone or in combination with other antiretrovirals. Truvada is notindicated for the treatment of chronic hepatitis B virus (HBV)infection and its safety and efficacy has not been established inpatients co-infected with HBV and HIV. Severe acute exacerbations ofhepatitis B have been reported in patients who have discontinuedViread or Emtriva. Hepatic function should be monitored closely withboth clinical and laboratory follow-up for at least several months inpatients who discontinue Truvada and are co-infected with HIV and HBV.If appropriate, initiation of anti-hepatitis B therapy may bewarranted.

There are no study results demonstrating the effect of Truvada onclinical progression of HIV-1, and it is not recommended that Truvadabe used as a component of a triple nucleoside regimen. Truvada shouldnot be used with Emtriva or Viread, or other drugs containinglamivudine, including Combivir, Epivir(R), Epivir-HBV(R), Epzicom(TM)or Trizivir(R). No drug interaction studies have been conducted usingTruvada. Drug interactions have been observed when didanosine,atazanavir, or lopinavir/ritonavir are co-administered with Viread, acomponent of Truvada, and dose adjustments may be necessary. Data arenot available to recommend a dose adjustment of didanosine forpatients weighing less than 60 kg. Patients on atazanavir orlopinavir/ritonavir plus Truvada should be monitored forTruvada-associated adverse events that may require discontinuation.When co-administered with Viread, it is recommended that atazanavir300 mg be given with ritonavir 100 mg. Atazanavir without ritonavirshould not be co-administered with Viread. Immune reconstitutionsyndrome has been reported in patients treated with combinationantiretroviral therapy, including Emtriva and Viread.

Two-hundred eighty-three patients have received combinationtherapy with Emtriva and Viread with either a non-nucleoside reversetranscriptase inhibitor or protease inhibitor for 24 to 48 weeks inongoing clinical studies. Based on these limited data, no new patternsof adverse events were identified and there was no increased frequencyof established toxicities.

Adverse events that occurred in more than 5 percent of patientsreceiving Emtriva with other antiretroviral agents in clinical trialsinclude abdominal pain, asthenia (weakness), headache, diarrhea,nausea, vomiting, dizziness and rash (rash, pruritis, maculopapularrash, urticaria, vesiculobullous rash, pustular rash and allergicreaction). Approximately 1 percent of patients discontinuedparticipation because of these events. All adverse events werereported with similar frequency in Emtriva and control treatmentgroups with the exception of skin discoloration which was reportedwith higher frequency in the Emtriva treated group. Skindiscoloration, manifested by hyperpigmentation on the palms and/orsoles, was generally mild and asymptomatic. The mechanism and clinicalsignificance are unknown.

The most common adverse events and those occurring in more than 5percent of patients receiving Viread with other antiretroviral agentsin clinical trials include asthenia, pain, abdominal pain, headache,nausea, diarrhea, vomiting, rash (rash, pruritis, maculopapular rash,urticaria, vesiculobullous rash and pustular rash), flatulence,dizziness and depression. Less than 1 percent of patients discontinuedparticipation because of gastrointestinal events. Renal impairment,including serious cases, has been reported. Renal impairment occurredmost often in patients with underlying systemic or renal disease or inpatients taking concomitant nephrotoxic agents, though some cases haveappeared in patients without identified risk factors. Decreases inbone mineral density (BMD) at the lumbar spine and hip and increasesin biochemical markers of bone metabolism have been seen with the useof Viread. The clinical significance of changes in BMD and biochemicalmarkers is unknown and follow-up is continuing to assess long-termimpact.

For complete prescribing information for Truvada, visitwww.truvada.com. For safety and efficacy studies using Emtriva orViread in combination with other antiretroviral agents, please consultthe prescribing information for these products.

About Gilead Sciences

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

This press release includes forward-looking statements, within themeaning of the Private Securities Litigation Reform Act of 1995, thatare subject to risks, uncertainties and other factors, including therisk that the safety and efficacy data obtained through the COMETstudy will not be observed through longer treatment periods or inother studies. These risks and uncertainties could cause actualresults to differ materially from those referred to in theforward-looking statements. Risks are described in detail in theGilead Annual Report on Form 10-K for the year ended December 31, 2004and in Gilead's Quarterly Reports on Form 10-Q, all of which are onfile with the U.S. Securities and Exchange Commission. Allforward-looking statements are based on information currentlyavailable to Gilead and Gilead assumes no obligation to update anysuch forward-looking statements.

For full prescribing information, please visit www.Truvada.com.

Truvada is a registered trademark of Gilead Sciences, Inc.

For more information on Gilead Sciences, please visit thecompany's website at www.gilead.com or call Gilead Public Affairs at1-800-GILEAD-5 or 1-650-574-3000.