GileadSciencesAnnouncesPlansforPhaseIVClinicalTrialEvaluatingFirst-LineCombinationTherapyVersusMonotherapyinPulmonaryArterialHypertension

FOSTER CITY, Calif.--(Business Wire)--
Gilead Sciences, Inc. (Nasdaq:GILD), in collaboration with GlaxoSmithKline
(GSK), today announced plans for an international, event-driven (morbidity and
mortality) clinical trial to study combination therapy versus monotherapy in a
first-line treatment setting for pulmonary arterial hypertension (PAH). The
study, AMBITION (a randomized, double-blind, multicenter study of first-line
combination therapy with AMBrIsentan and Tadalafil in subjects with pulmonary
arterial hypertensION),will evaluate first-line combination use with
ambrisentan, an endothelin receptor antagonist (ERA) and tadalafil, a PDE5
inhibitor, in patients with PAH. Ambrisentan is approved under the tradename
Letairis® (ambrisentan 5 mg and 10 mg tablets) as a once-daily treatment for PAH
(WHO Group 1) in patients with WHO functional class II or III symptoms to
improve exercise capacity and delay clinical worsening.

"The question of first-line combination therapy versus monotherapy is one of the
most important outstanding clinical questions in PAH," said Lewis J. Rubin, MD,
Professor of Medicine, University of California, San Diego. "As the first large,
randomized clinical trial to address the efficacy of initial combination therapy
in PAH, AMBITION has the potential to be a landmark study."

AMBITION will be a double-blind, multicenter study, in which more than 300
treatment-naive PAH patients will be randomized to receive either the
combination of ambrisentan and tadalafil or monotherapy (ambrisentan or
tadalafil). Gilead and GSK are working with regulatory agencies and the PAH
research community to finalize details of the study and plan to begin enrollment
in 2010.

Full prescribing information for Letairis is available at www.gilead.com and at
http://www.letairis.com/downloads/LETAIRIS_prescribing_information.pdf.

WARNING: POTENTIAL LIVER INJURY

Letairis can cause elevation of liver aminotransferases (ALT and AST) to at
least three times the upper limit of normal (ULN). Letairis treatment was
associated with aminotransferase elevations greater than three times ULN in 0.8
percent of patients in 12-week trials and 2.8 percent of patients including
long-term open-label trials out to one year. One case of aminotransferase
elevations greater than three times ULN has been accompanied by bilirubin
elevations greater than two times ULN. Because these changes are a marker for
potentially serious liver injury, serum aminotransferase levels (and bilirubin
if aminotransferase levels are elevated) must be measured prior to initiation of
treatment and then monthly.

Elevations in aminotransferases require close attention. Letairis should
generally be avoided in patients with elevated aminotransferases greater than
three times ULN at baseline because monitoring liver injury may be more
difficult. If liver aminotransferase elevations are accompanied by clinical
symptoms of liver injury (such as nausea, vomiting, fever, abdominal pain,
jaundice, or unusual lethargy or fatigue) or increases in bilirubin greater than
two times ULN, treatment should be stopped. There is no experience with the
re-introduction of Letairis in these circumstances.

CONTRAINDICATION: PREGNANCY

Letairis is very likely to produce serious birth defects if used by pregnant
women, as this effect has been seen consistently when it is administered to
animals. Pregnancy must therefore be excluded before the initiation of treatment
with Letairis and prevented thereafter and for one month after stopping
treatment by the use of two acceptable methods of contraception unless the
patient has had a tubal sterilization or chooses to use a Copper T 380A IUD or
LNg 20 IUS, in which case no additional contraception is needed. Obtain monthly
pregnancy tests.

About the Letairis Education and Access Program (LEAP)

Because of the risks of liver injury and birth defects, Letairis is available
only through a special restricted distribution program called the Letairis
Education and Access Program (LEAP) by calling 1-866-664-LEAP (1-866-664-5327).
Only prescribers and pharmacies registered with LEAP are able to prescribe and
distribute Letairis. In addition, Letairis may be dispensed only to patients who
are enrolled in and meet all conditions of LEAP.

Important Safety Information

Decreases in hemoglobin concentration and hematocrit have followed
administration of other endothelin receptor antagonists and were observed in
clinical studies with Letairis. These decreases were observed within the first
few weeks of treatment with Letairis, and stabilized thereafter. Physicians
should measure hemoglobin prior to initiation of Letairis, at one month, and
periodically thereafter. Initiation of Letairis therapy is not recommended for
patients with clinically significant anemia.

Peripheral edema is a known class effect of endothelin receptor antagonists and
is also a clinical consequence of PAH and worsening PAH. In the
placebo-controlled studies, there was an increased incidence of peripheral edema
in patients treated with doses of 5 or 10 mg of Letairis compared to placebo.
Most edema was mild to moderate in severity. Peripheral edema was similar in
younger patients (age less than 65 years) receiving Letairis (14 percent;
29/205) or placebo (13 percent; 13/104), and was greater in elderly patients
(age greater than or equal to 65 years) receiving Letairis (29 percent; 16/56)
compared to placebo (4 percent, 1/28). The results of such subgroup analyses
must be interpreted cautiously.

In addition, there have been post-marketing reports of fluid retention in
patients with pulmonary hypertension, occurring within weeks after starting
Letairis. Patients required intervention with a diuretic, fluid management, or,
in some cases, hospitalization for decompensating heart failure. Because the
post-marketing experience was reported voluntarily from a population of
uncertain size, it is not possible to reliably estimate the relative frequency
or establish a causal relationship to Letairis drug exposure.

Decreases in sperm count have been observed in patients taking endothelin
receptor antagonists.

The most common adverse events that occurred at a higher frequency among
Letairis-treated patients compared to placebo included (placebo-adjusted
frequency): peripheral edema (6 percent), nasal congestion (4 percent),
sinusitis (3 percent), flushing (3 percent), palpitations (3 percent), nasal
pharyngitis (2 percent), abdominal pain (2 percent), constipation (2 percent),
dyspnea (1 percent) and headache (1 percent).

No clinically relevant interactions of Letairis with warfarin, sildenafil,
tadalafil, omeprazole (CYP2C19 inhibitor), ketoconazole (strong
CYP3A-inhibitor), digoxin, ethinylestradiol or norethindrone have been observed.

Other potential interactions are not well characterized, but, based on in vitro
data, interactions with P-glycoprotein (P-gp), the Organic Anion Transport
Protein (OATP), and uridine 5′-diphosphate glucuronosyltransferases (UGTs) would
be expected.

Letairis is not recommended in patients with moderate to severe hepatic
impairment.

About Letairis

Letairis (ambrisentan) is an endothelin receptor antagonist that has a high
affinity for the endothelin type-A (ETA) receptor. Activation of the ETA
receptor by endothelin-1 (ET-1), a small peptide hormone, leads to
vasoconstriction (narrowing of blood vessels) and cell proliferation. The
clinical impact of high selectivity for ETA is not known. Endothelin
concentrations are higher in the lung tissue of PAH patients, thus suggesting
that ET-1 may play a critical role in the pathogenesis or progression of PAH.

About Pulmonary Arterial Hypertension (WHO Group 1)

PAH is a debilitating disease characterized by constriction of the blood vessels
in the lungs leading to high pulmonary arterial pressures. These high pressures
make it difficult for the heart to pump blood through the lungs to be
oxygenated. Patients with PAH suffer from shortness of breath as the heart
struggles to pump against these high pressures, causing such patients to
ultimately die of heart failure. PAH can occur with no known underlying cause,
or it can occur secondary to diseases such as connective tissue disease,
congenital heart defects, cirrhosis of the liver and HIV infection. PAH afflicts
approximately 200,000 patients worldwide.

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.

This press release includes forward-looking statements, within the meaning of
the Private Securities Litigation Reform Act of 1995, that are subject to risks,
uncertainties and other factors, including the risks that Gilead and GSK may
face challenges in the clinical trial protocol design and may be unable to
enroll patients in the trial in 2010 as currently anticipated. In addition, the
results from the clinical trial may be unfavorable, including showing no
advantages from combination therapy resulting from use of ambrisentan with
tadalafil. These risks, uncertainties and other factors could cause actual
results to differ materially from those referred to in the forward-looking
statements. The reader is cautioned not to rely on these forward-looking
statements. These and other risks are described in detail in Gilead`s Quarterly
Report on Form 10-Q for the second quarter of 2009, as filed with the U.S.
Securities and Exchange Commission. All forward-looking statements are based on
information currently available to Gilead, and Gilead assumes no obligation to
update any such forward-looking statements.

Letairis is a registered trademark of Gilead Sciences, Inc.

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

Gilead Sciences, Inc.
Susan Hubbard, Investors, 650-522-5715
Nathan Kaiser, Media, 650-522-1853

Copyright Business Wire 2009