Data Comparing Viread(R) and Emtriva(R) to Combivir(R) as Part of Combination HIV Therapy Published in New England Journal of Medicine

Gilead Sciences, Inc. (Nasdaq:GILD) today announced thepublication of 48-week data from a clinical trial (Study 934)comparing a once-daily treatment regimen of Viread(R) (tenofovirdisoproxil fumarate), Emtriva(R) (emtricitabine) and Sustiva(R)(efavirenz) to a twice-daily regimen of Combivir(R)(lamivudine/zidovudine) with Sustiva once daily in treatment-naivepatients with HIV. Data appearing in the January 19 issue of NewEngland Journal of Medicine (N Engl J Med 2006; 354;3, 251-260) showthat a significantly greater percentage of patients taking a regimencontaining Viread and Emtriva achieved and maintained HIV RNA lessthan 400 copies/mL, with fewer side effects that resulted in studydiscontinuation, and had a greater increase in CD4 cell countscompared to patients taking a Combivir-based regimen.

Viread and Emtriva are often prescribed together as a fixed-dosecombination tablet called Truvada(R) (emtricitabine and tenofovirdisoproxil fumarate), which became commercially available after Study934 began. Both Truvada and Combivir are widely used fixed-dosecombination medicines from the nucleoside reverse transcriptaseinhibitor (NRTI) class of antiretrovirals. NRTIs are commonly regardedas the "backbone" of combination therapy for HIV.

"Data like these are important to help define ways for physiciansto simplify effective HIV therapy for treatment-naive patients," saidJoel Gallant, MD, Johns Hopkins University School of Medicine,Baltimore, a lead investigator for the study and lead author of thepaper. "Even with the remarkable advances made in the field of HIVmedicine in the last 10 years, there is still a need for improved andsimplified therapy."

About Study 934

Study 934 is a Phase III, multicenter, open-label clinical trialthat enrolled 517 HIV-infected patients in the United States andEurope. The study's primary endpoint was at 48 weeks. The prespecifiedprimary efficacy population included 487 patients. Participants in onearm of the study received Viread 300 mg, Emtriva 200 mg and Sustiva600 mg, all dosed once daily. Patients in the comparator arm receivedCombivir twice daily and Sustiva 600 mg once daily. At study entry,patients had not previously received antiretroviral therapy and hadHIV RNA (viral load) greater than 10,000 copies/mL. The study isplanned to continue through 144 weeks.

For the 48 week (n=487) primary endpoint of the study, 84 percentof patients in the Viread/Emtriva arm compared to 73 percent ofpatients in the Combivir arm achieved and maintained HIV RNA less than400 copies/mL through week 48 using the Time to Loss of VirologicResponse algorithm (TLOVR) (p=0.002; 95% CI, +4% to +19%). Similarly,80 percent of patients in the Viread/Emtriva arm compared to 70percent of patients in the Combivir arm achieved and maintained HIVRNA less than 50 copies/mL through week 48 using the TLOVR algorithm(p=0.02; 95% CI, +2% to +17%). Patients receiving Viread/Emtriva had asignificantly greater increase from baseline in CD4 cell counts atweek 48 compared to those receiving Combivir (190 vs. 158 cells/mm3;p=0.002; 95% CI, +9 cells/mm3 to +55 cells/mm3).

Genotypic data were collected for 35 patients with HIV that metthe criteria for resistance analyses. Resistance analysis includedpatients who had HIV RNA greater than 400 copies/mL either at week 48,or for two consecutive visits after having achieved viral suppressionbelow 400 copies on at least one occasion, or who discontinued priorto week 48 but had HIV RNA greater than 400 copies mL on their lastvisit prior to discontinuation. Twenty-two patients with baselineNNRTI resistance were excluded from the analysis. There were nosignificant differences between the two treatment groups, and the mostcommon resistance mutations that developed were associated withSustiva. No patient developed the K65R mutation, which is associatedwith resistance to Viread.

The 48-week safety analysis for Study 934 is based on 511 patientswho received any study medication. A significantly (p=0.02) greaterpercentage of patients in the Combivir group (9 percent) experiencedadverse events that resulted in the discontinuation of studymedications compared to the Viread/Emtriva arm (4 percent). The mostcommon cause of discontinuation related to study drug for patients inthe Combivir arm was anemia (14 patients, vs. 0 in the Viread/Emtrivaarm; p less than 0.001) and in the Viread/Emtriva arm wasNNRTI-associated rash, which occurred in 2 patients. Renal safety wassimilar in the two groups and no patient discontinued study medicationdue to renal events.

A significantly (p less than 0.001) greater percentage of patientsin the Viread/Emtriva arm of the study had a lower mean increase frombaseline in fasting total cholesterol levels (21 mg/dL) compared topatients in the Combivir arm (35 mg/dL). At week 48, total limb fatwas significantly less in a subset of patients receiving Combivir(mean of 6.9 kg or 15.2 pounds; n=49) compared to a subset of patientsreceiving Viread and Emtriva (mean of 8.9 kg or 19.6 pounds; n=51;p=0.03).

Data from Study 934 have not been reviewed by the U.S. Food andDrug Administration (FDA). It is important that patients be aware thatindividual HIV medications must be taken as part of combinationregimens, and that they do not cure HIV infection or preventtransmitting HIV to other people.

Joint Venture to Develop Fixed-Dose Regimen of Truvada and Sustiva

On December 20, 2004, Gilead and Bristol-Myers Squibb (BMS)announced the establishment of a U.S. joint venture to develop andcommercialize a once-daily fixed-dose combination of Truvada andSustiva. Gilead and BMS announced on January 9, 2006 that thecompanies have obtained data supporting bioequivalence of a newformulation of the fixed-dose combination with the components thatmake up the combination and expect to file a new drug application withthe FDA in the second quarter of this year.

About HIV/AIDS

2006 marks the 25th anniversary of the start of the AIDS epidemic.The first cases of HIV/AIDS were reported by the U.S. Centers forDisease Control and Prevention (CDC) in the June 5, 1981 issue of theMorbidity and Mortality Weekly Report (MMWR). Today, CDC estimatesthat more than one million Americans are infected with HIV, the virusthat causes acquired immunodeficiency syndrome (AIDS). Of these,approximately 25 percent are unaware of their infection. Although HIVtreatment options have expanded rapidly in recent years, CDC estimatesthat 216,000 Americans who are HIV infected and eligible forantiretroviral treatment are currently not receiving it.

Ensuring Access in Developing World Countries

The parent compound of Viread was discovered through acollaborative research effort between Dr. Antonin Holy, Institute forOrganic Chemistry and Biochemistry, Academy of Sciences of the CzechRepublic (IOCB) in Prague and Dr. Erik DeClercq, Rega Institute forMedical Research, Katholic University in Leuven, Belgium. Theinventors have agreed to waive their right to a royalty on sales ofproducts containing tenofovir in the 97 developing countries served bythe Gilead Access Program to ensure the product can be offered at ano-profit price in parts of the world where the AIDS epidemic has hitthe hardest.

Important Safety Information from U.S. Prescribing Information forTruvada, Emtriva and Viread

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, Emtrivaand Viread are not indicated for the treatment of chronic hepatitis Bvirus (HBV) infection and the safety and efficacy of these drugs hasnot been established in patients co-infected with HBV and HIV. Severeacute exacerbations of hepatitis B have been reported in patients whohave discontinued Emtriva or Viread. Hepatic function should bemonitored closely with both clinical and laboratory follow-up for atleast several months in patients who discontinue Truvada, Emtriva orViread and are co-infected with HIV and HBV. If appropriate,initiation of anti-hepatitis B therapy may be warranted.

Changes in body fat have been observed in patients taking Truvada,Emtriva and Viread and other anti-HIV medicines. The cause and longterm health effect of this condition is unknown. Immune reconstitutionsyndrome has been reported in patients treated with combinationantiretroviral therapy, including Truvada, Emtriva and Viread.

About Truvada

Truvada is a fixed-dose combination of Emtriva and Viread. Truvadacombines 200 mg of emtricitabine and 300 mg of tenofovir disoproxilfumarate in one tablet, taken once a day in combination with otherantiretroviral agents. In the United States, Truvada is indicated incombination with other antiretroviral agents (such as non-nucleosidereverse transcriptase inhibitors or protease inhibitors) for thetreatment of HIV-1 infection in adults. Safety and efficacy studiesusing Truvada tablets or using Emtriva and Viread in combination areongoing.

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.

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.

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. For additional safety information aboutEmtriva or Viread in combination with other antiretroviral agents,please see "About Emtriva" and "About Viread," below.

About Emtriva

In the United States, Emtriva is indicated, in combination withother antiretroviral agents, for the treatment of HIV-1 infection inpatients over three months of age. This indication is based onanalyses of plasma HIV-1 RNA levels and CD4 cell counts fromcontrolled studies of 48 weeks duration in antiretroviral-naivepatients and antiretroviral-treatment-experienced patients who werevirologically suppressed on an HIV treatment regimen. Inantiretroviral-treatment-experienced patients, the use of Emtriva maybe considered for patients with HIV strains that are expected to besusceptible to Emtriva as assessed by genotypic or phenotypic testing.

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. For pediatric patients over three months ofage, the adverse event profile observed during clinical trials wassimilar to that of adult patients, with the exception of anemia and ahigher frequency of hyperpigmentation.

About Viread

In the United States, Viread is indicated in combination withother antiretroviral agents for the treatment of HIV-1 infection. Thisindication is based on analyses of plasma HIV-1 RNA levels and CD4cell counts in controlled studies of Viread in treatment-naive adultsand in treatment-experienced adults. There are no study resultsdemonstrating the effect of Viread on clinical progression of HIV-1.The use of Viread should be considered for treating adult patientswith HIV-1 strains that are expected to be susceptible to tenofovir asassessed by laboratory testing or treatment history.

Renal impairment, including cases of acute renal failure andFanconi syndrome (renal tubular injury with severe hypophosphatemia),has been reported. Renal impairment occurred most often in patientswith underlying systemic or renal disease or in patients takingconcomitant nephrotoxic agents, though some cases have appeared inpatients without identified risk factors. Decreases in bone mineraldensity (BMD) at the lumbar spine and hip 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. The most common adverse events and those occurring in morethan 5 percent of patients receiving Viread with other antiretroviralagents in clinical trials include asthenia, pain, abdominal pain,headache, nausea, diarrhea, vomiting, rash (rash, pruritis,maculopapular rash, urticaria, vesiculobullous rash and pustularrash), flatulence, dizziness and depression. Less than 1 percent ofpatients discontinued participation because of gastrointestinalevents.

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 48 weeks ofStudy 934 will not be observed in other studies or clinical practiceand risks associated with the inclusion of these data in the labelsfor Truvada or Viread. These risks and uncertainties could causeactual results 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,www.Viread.com and www.Emtriva.com.

Truvada, Viread and Emtriva are registered trademarks of GileadSciences, 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.