NewDataforGileadSciences`AmbrisentanShowClinicalImprovementsin a DiversePulmonaryHypertension(PH)Population

SAN DIEGO--(Business Wire)--
Gilead Sciences, Inc. (Nasdaq: GILD) today announced results from ARIES-3, an
open-label, single-arm, Phase III study evaluating the efficacy and safety of
ambrisentan in patients with pulmonary hypertension (PH), which showed a mean
21-meter improvement from baseline in six-minute walk distance (6MWD) at 24
weeks. Ambrisentan is approved under the tradename Letairis® (ambrisentan 5 mg
and 10 mg tablets) as a once-daily treatment for pulmonary arterial hypertension
(PAH) (WHO Group 1) in patients with WHO functional class II or III symptoms to
improve exercise capacity and delay clinical worsening. The ARIES-3 study
included patients with PAH (WHO Group 1) as well as patients with pulmonary
hypertension due to other etiologies (WHO Groups 3, 4 and 5). Data from this
study were presented today at the 2009 American Thoracic Society (ATS)
International Conference, taking place May 15-20 in San Diego.

"In previous clinical trials, ambrisentan has been shown to improve exercise
capacity and delay clinical worsening in WHO Group 1 PAH patients with WHO
functional class II and III symptoms," said David Badesch, MD, Professor of
Medicine and Clinical Director of the Pulmonary Hypertension Center at the
University of Colorado Health Sciences Center and lead study author. "However,
many patients seen in clinical practice have pulmonary hypertension associated
with other diseases. ARIES-3 is important because it represents the first safety
and efficacy data for ambrisentan in a more diverse PH patient population,
including patients already on background therapy."

About ARIES-3

ARIES-3 was an open-label, single-arm, multicenter, Phase III study designed to
evaluate the efficacy and safety of ambrisentan in a broader PH population than
was studied in the ARIES-1 and ARIES-2 studies. The study enrolled 224 patients
with WHO Group 1 PAH (n=140) or PH due to other etiologies (n=84), including 23
patients with PH secondary to chronic obstructive pulmonary disease (PH-COPD)
(WHO Group 3), 21 patients with PH secondary to interstitial lung disease
(PH-ILD) (WHO Group 3) and 29 patients with PH due to chronic thromboembolic
disease (CTEPH) (WHO Group 4). Patients received ambrisentan at a dose of 5 mg
once daily until the primary analysis of efficacy at 24 weeks. The primary
endpoint was the change from baseline in 6MWD at Week 24. Secondary objectives
were to evaluate the effects of ambrisentan on other clinical measures of PH,
including the number of patients still alive at specified time points and time
to clinical worsening, which was defined as the time from initiation of
ambrisentan to the first occurrence of death, lung transplantation,
hospitalization for PH, atrial septostomy, a change to chronic prostanoid
therapy or sildenafil due to protocol-defined worsening criteria or study
withdrawal due to addition of other PH medications. In addition, the safety and
tolerability of ambrisentan was evaluated in the overall study population and in
various subgroups.

At baseline, 29 percent of patients were classified as having WHO functional
class II symptoms and 65 percent of patients had WHO functional class III
symptoms. The mean baseline 6MWD for patients was 317±84 meters. At baseline, 52
percent of all patients were receiving sildenafil and/or prostanoid therapy.
Twenty-seven patients in the study had previously discontinued use of bosentan
and/or sitaxsentan due to liver enzyme (aminotransferase) elevations greater
than three times the upper limit of normal (ULN).

In the overall study population, patients experienced a mean 6MWD improvement of
21 meters (95 percent CI: 11.8 to 29.3; p<0.001) from baseline at 24 weeks. At
24 weeks, 97 percent of patients were still alive (95 percent CI: 94 to 99). The
probability of no clinical worsening at 24 weeks across all patients was 90
percent (95 percent CI: 85 to 93), as assessed by Kaplan-Meier estimates.

Six (2.7 percent) of the 224 patients experienced aminotransferase elevations
greater than three times ULN during the 24-week study period. Two (0.8 percent)
of these patients discontinued treatment due to aminotransferase elevations
greater than eight times ULN. Of the 27 patients who had previously discontinued
bosentan and/or sitaxsentan due to aminotransferase abnormalities prior to
ARIES-3 study entry, one patient experienced a recurrence of aminotransferase
elevation greater than three times ULN.

The most frequent adverse events occurring in greater than or equal to 10
percent of patients during the 24-week study period were peripheral edema,
headache, dyspnea, upper respiratory tract infection, nasal congestion, fatigue
and nausea. Most reports of peripheral edema were reported to be mild or
moderate in severity. The most frequent adverse events leading to
discontinuation were peripheral edema (n=7), right ventricular failure (n=4) and
pulmonary hypertension (n=3). Patients could have had more than one adverse
event leading to study withdrawal.

As study ARIES-3 is not placebo-controlled, these findings do not allow for
comparison with a group not given ambrisentan and cannot be used to definitively
determine the efficacy and safety of ambrisentan. Similarly, due to the small
sample sizes and open-label design of the study, no definitive conclusions
regarding efficacy and safety can be drawn from the subgroup analyses observed
in this study.

Letairis is approved for the treatment of PAH (WHO Group 1) with WHO functional
class II and III symptoms to improve exercise capacity and delay clinical
worsening and is not indicated for other PH classifications, such as CTEPH or PH
associated with COPD or ILD. 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 by the use of at least two reliable
methods of contraception unless the patient is unable to become pregnant. 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.

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.

Caution should be used when Letairis is co-administered with cyclosporine A, as
it may cause increased exposure to Letairis.

Caution should be used when Letairis is co-administered with strong
CYP3A-inhibitors (e.g., ketoconazole) or CYP2C19-inhibitors (e.g., omeprazole).

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 or sildenafil have
been observed.

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.

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, 650-522-5715 (Investors)
Nathan Kaiser, 650-522-1853 (Media)

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