Gilead Announces Presentation of Long-Term Data for Ambrisentan, a Potential Treatment for Patients With Pulmonary Arterial Hypertension

Gilead Sciences, Inc. (Nasdaq:GILD) today announced results of two
long-term studies evaluating ambrisentan, an investigational
endothelin receptor antagonist (ERA) for the treatment of patients
with pulmonary arterial hypertension (PAH). These long-term data are
from patients who originally participated in the two pivotal Phase III
ARIES studies and AMB-222, a Phase II study of patients who had
previously discontinued other ERAs because of liver function
abnormalities. These studies were selected for oral presentation at
ATS 2007, the International Conference of the American Thoracic
Society, taking place in San Francisco, California, May 18-23.

"Pulmonary arterial hypertension is a progressive,
life-threatening disease for which new therapies are clearly needed,"
said Ronald J. Oudiz, MD, Associate Professor of Medicine, UCLA School
of Medicine and Director, Liu Center for Pulmonary Hypertension, Los
Angeles Biomedical Research Institute at Harbor-UCLA Medical Center.
"The long-term clinical profile observed in these ambrisentan studies
is very encouraging."

About the Studies

In the first presentation (Abstract #2307), Dr. Oudiz presented
results from an integrated analysis of an ongoing, long-term extension
study (ARIES-E) involving patients from the two 12-week Phase III
placebo-controlled studies (ARIES-1 and ARIES-2). A total of 383
patients with idiopathic PAH or PAH associated with connective tissue
disease, HIV infection, or anorexigen use who received at least one
dose of ambrisentan (2.5, 5 or 10 mg once-daily) in ARIES-1, ARIES-2
or ARIES-E were included in the integrated analysis, which reflect
data available as of February 2006 (mean exposure = 39 weeks; maximum
exposure = 109 weeks).

Improvements in the non placebo-corrected 6-minute walk distance
observed during the first 12 weeks of ambrisentan treatment (+37.7
meters) were sustained for at least 48 weeks (+36.4 meters).
Improvements in WHO functional class and Borg dyspnea index were also
maintained with long-term ambrisentan treatment. In addition, the
one-year probability of survival was 95 percent for patients receiving
ambrisentan.

Ambrisentan adverse events were similar in nature to those
reported in the previous 12-week placebo-controlled studies. The most
common adverse event was peripheral edema which was generally reported
to be mild or moderate and did not lead to discontinuation of
ambrisentan.

As of October 2006 (mean exposure = 1.4 years; maximum exposure =
2.8 years), 2.1 percent of patients developed liver enzyme
(aminotransferase) elevations greater than three times the upper limit
of normal, which was similar to the incidence observed for the placebo
groups (2.3 percent) in the 12-week ARIES-1 and ARIES-2 studies. One
patient required discontinuation of ambrisentan due to liver enzyme
abnormalities.

Long-term results from the AMB-222 study (Abstract #2171) were
presented by Michael McGoon, MD, Professor of Medicine, Mayo Clinic,
Rochester, Minnesota. This open-label study evaluated 36 patients who
had previously discontinued the ERAs bosentan (86 percent),
sitaxsentan (6 percent), or both (8 percent) due to the development of
liver function abnormalities. In this study, patients with idiopathic
PAH or PAH associated with connective tissue disease, congenital heart
defects, HIV infection, or anorexigen use received once-daily doses of
ambrisentan -- 2.5 mg/day for four weeks, 5 mg/day for 20 weeks, and
2.5, 5 or 10 mg/day thereafter -- for up to 18 months. Twenty-five of
the 36 patients enrolled were also receiving concomitant sildenafil
and/or prostanoid treatment. The primary endpoint of the study was the
incidence of liver function abnormalities during 12 weeks of therapy
that resulted in discontinuation of drug.

No patients had liver function abnormalities that required
discontinuation of ambrisentan during the 12-week primary endpoint
period. Of the 36 patients evaluated, two patients discontinued due to
adverse events not related to liver toxicity. As of October 2006 (mean
exposure = 1.1 years, maximum duration 1.4 years), one patient had
developed a transient liver function abnormality that was greater than
three times the upper limit of normal and this patient continued
receiving treatment with ambrisentan. The long-term adverse event
profile appeared similar to results from previous ambrisentan clinical
studies and included peripheral edema, headache, dyspnea and flushing.

"Endothelin receptor antagonism has well-established clinical
benefits in patients with PAH, but liver toxicity, which frequently
leads to discontinuation of treatment, has limited the usefulness of
these drugs in some patients," said Dr. McGoon. "The results of this
study support the potential of ambrisentan in newly diagnosed patients
with PAH, as well as patients who have failed other ERA therapies due
to liver function abnormalities."

"PAH is a chronic disease and, as such, we recognize the
importance of evaluating the long-term efficacy and safety profile of
ambrisentan," said Michael J. Gerber, MD, Senior Vice President,
Clinical Research at Gilead. "We will continue to work with the
clinical investigators and follow patients from each of these studies
so we can better understand the benefits and risks of ambrisentan with
long-term treatment."

In addition to these long-term ambrisentan data presentations, two
posters describing an integrated analysis of 12-week ARIES-1 and
ARIES-2 data are also being presented at ATS. The first poster
(Abstract #3192) titled "Ambrisentan Therapy for Pulmonary Arterial
Hypertension: An Integrated Analysis of the ARIES-1 and ARIES-2
Studies" was presented today by Nazzareno Galie, MD, Professor of
Cardiology at the University of Bologna in Bologna, Italy. The second
poster (Abstract #2873) titled "Ambrisentan Improves Exercise Capacity
and Dyspnea in WHO Functional Class II and Class III Patients with
Pulmonary Arterial Hypertension" will be presented on Wednesday, May
23 by Horst Olschewski, MD, Professor of Medicine in the Division of
Pulmonology at the Medical University of Graz in Graz, Austria.

About Ambrisentan

Ambrisentan is a non-sulfonamide, propanoic acid-class, endothelin
receptor antagonist that is selective for the endothelin type-A (ETA)
receptor. Activation of the ETA receptor by endothelin, a small
peptide hormone, leads to vasoconstriction (narrowing of blood
vessels) and cell proliferation. PAH is associated with elevated
endothelin blood levels. Ambrisentan has been granted orphan drug
designation for the treatment of PAH in both the United States and
European Union.

The U.S. Food and Drug Administration (FDA) recently accepted for
filing and granted a Priority Review for Gilead's New Drug Application
(NDA) for marketing approval of ambrisentan (5 mg and 10 mg) for the
once-daily treatment of PAH. The FDA has established a target review
date, under the Prescription Drug User Fee Act (PDUFA), of June 18,
2007.

As an investigational compound, ambrisentan has not yet been
determined safe or efficacious in humans.

GlaxoSmithKline holds rights to commercialize ambrisentan for PAH
in territories outside of the United States. A Marketing Authorisation
Application (MAA) for ambrisentan was filed with the European
Medicines Agency (EMEA) earlier this year.

About Pulmonary Arterial Hypertension

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. 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.

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 risks
related to Gilead's ability to successfully commercialize ambrisentan
for PAH. For example, the FDA may not approve ambrisentan for the
treatment of PAH in the United States, and marketing approval, if
granted, may have significant limitations on its use. In addition,
future discussions with the FDA may impact the amount of data needed
and timelines for review, which may differ materially from Gilead's
current projections. Further, safety and efficacy data from additional
clinical studies may not warrant further development of this compound
and completing our clinical studies may take longer or cost more than
expected. 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 Annual Report on Form 10-K for the year ended
December 31, 2006 and its Report on Form 10-Q for the first quarter of
2007, 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.