Gilead Announces Detailed Results of Phase III Study of Aztreonam Lysine for Inhalation in Patients With Cystic Fibrosis

Gilead Sciences, Inc. (Nasdaq:GILD) today announced detailed
results of its Phase III AIR-CF1 (CP-AI-007) study of aztreonam lysine
for inhalation, an investigational therapy in development for the
treatment of people with cystic fibrosis (CF) who have pulmonary
Pseudomonas aeruginosa (P. aeruginosa). In this study, a 28-day
treatment course of aztreonam lysine improved respiratory symptoms as
assessed by the Cystic Fibrosis Questionnaire-Revised (CFQ-R), a
patient-reported outcome (PRO) tool. Aztreonam lysine also improved
pulmonary function in this study, as measured by relative improvement
of forced expiratory volume in one second (FEV1), a standard measure
of lung function. The data were presented by George Z. Retsch-Bogart,
MD, Associate Professor of Pediatrics at the University of North
Carolina, Chapel Hill, at the 21st Annual North American Cystic
Fibrosis Conference (NACFC) in Anaheim, California. Topline results
from this study were previously announced on May 29, 2007.

"Cystic fibrosis causes a type of chronic lung disease that is
characterized by recurring or persistent bacterial infection, which
leads to gradually declining lung function, exercise capacity and
quality of life," said Dr. Retsch-Bogart. "These study results are
particularly encouraging, given that patients experienced meaningful
improvements as measured by both patient-reported respiratory symptoms
and also traditional pulmonary function endpoints such as FEV1."

AIR-CF1 was a randomized, double-blind, placebo-controlled study
designed to assess the safety and efficacy of a 28-day treatment
course of aztreonam lysine in people with CF who have pulmonary P.
aeruginosa. In this study, 164 patients were randomized to receive 28
days of treatment with 75 mg aztreonam lysine (n=80) or volume-matched
placebo (n=84) administered three times daily (TID) by the PARI
eFlow(R) Electronic Nebulizer. Patients were followed for an overall
study period of 42 days, with 14 days of observation after completing
aztreonam lysine or placebo therapy. The mean age of patients treated
with aztreonam lysine in the trial was 27.4 years. At baseline, the
mean overall CFQ-R score in the respiratory symptoms domain was 60.7
points (on a scale of 100). The mean percent predicted FEV1 was 54.6
percent overall. Thirty-seven percent of patients had a predicted FEV1
less than or equal to 50 percent, indicating severe baseline
impairment of lung function.

After 28 days of treatment, patients in the aztreonam lysine group
experienced a significant improvement in mean change from baseline of
9.71 points in the respiratory symptoms domain of the CFQ-R compared
to patients receiving placebo (p=0.0005). Aztreonam lysine-treated
patients also experienced significant improvements from baseline in
pulmonary function, as measured by relative improvement of FEV1, with
a treatment difference in mean change from baseline of 10.3 percent
versus placebo (p less than 0.0001).

Aztreonam lysine was also associated with significantly greater
reductions in P. aeruginosa colony forming units (a measure of the
amount of bacteria present in the lungs) at 28 days compared with
placebo, with a treatment difference in mean change from baseline of
-1.45 (log reduction, p less than 0.0001). Minor fluctuations in
pseudomonas sensitivity to aztreonam were seen (as measured by minimum
inhibitory concentrations) from baseline to the end of therapy.
Long-term data are needed to fully assess this aspect of therapy.

There was also a trend toward lower rates of hospitalization among
aztreonam lysine-treated patients compared to placebo-treated patients
(5.0 percent versus 14.3 percent, respectively, p = 0.0640).

Aztreonam lysine was well-tolerated with a safety profile
consistent with the expected symptoms of a patient with underlying CF
disease. The most common treatment-emergent adverse events in this
study were cough (47.5 percent), productive cough (16.3 percent),
nasal congestion (13.8 percent), sore throat (12.5 percent) and
dyspnea (shortness of breath) (8.8 percent). Among these, productive
cough was reported significantly less frequently in the aztreonam
lysine group compared to the placebo group. The remaining events were
not significantly different between the placebo and aztreonam lysine
groups.

Limited interim data from AIR-CF3 (CP-AI-006), an open-label
extension study of patients who participated in AIR-CF1 and AIR-CF2,
will also be described by Felix Ratjen, MD, PhD, FRCPC, Head, Division
of Respiratory Medicine, Sellers Chair of Cystic Fibrosis at The
Hospital for Sick Children and Professor of Paediatrics at the
University of Toronto, during a plenary session titled, "CF Drug
Development: What's New?" on Friday, October 5. CFQ-R and FEV1
responses similar to what were seen in the placebo-controlled trials
were reported after each of the first three 28-day courses of three
times daily aztreonam lysine therapy given in 28-day on, 28-day off
cycles.

Aztreonam lysine for inhalation is an investigational therapy and
has not yet been determined safe or efficacious in humans.

About AIR-CF Phase III Clinical Program

AIR-CF1 was one of three Phase III studies in the AIR-CF clinical
program. The program, which also includes AIR-CF2 and AIR-CF3, was
designed to determine the safety and efficacy of aztreonam lysine for
inhalation for treatment of people with CF who have pulmonary P.
aeruginosa.

AIR-CF2 was a randomized, double-blind, placebo-controlled study
designed to assess the safety and efficacy of a 28-day treatment
course with aztreonam lysine for inhalation following a 28-day
treatment course of tobramycin inhalation solution in people with CF
who have pulmonary P. aeruginosa. Patients were randomized to receive
28 days of treatment with 75 mg of aztreonam lysine or volume-matched
placebo each administered twice daily (BID) or TID by the PARI eFlow
Electronic Nebulizer. Patients were followed for an overall study
period of 126 days, with 56 days of observation after receiving
aztreonam lysine for inhalation therapy or placebo. Positive results
from this study were presented at the Cystic Fibrosis Therapeutics
Development Network conference in Seattle, Washington on April 19,
2007 and at the European Cystic Fibrosis Society Conference in Belek,
Turkey on June 14, 2007.

AIR-CF3 is an ongoing open-label, multi-center study of patients
who participated in the AIR-CF1 or AIR-CF2 studies. The primary
objective of the study is to evaluate the safety of repeated exposure
to aztreonam lysine for inhalation in people with CF. Each patient's
participation in the study will last up to 18 months. Patients will
receive treatment with 75 mg of aztreonam lysine with the same regimen
they received in AIR-CF1 or AIR-CF2 (BID or TID).

About the Expanded Access Program

In August 2007, Gilead initiated an expanded access program (EAP)
to provide aztreonam lysine for inhalation to patients with CF and P.
aeruginosa who have limited treatment options and are at risk for
disease progression. The EAP is open to treatment centers in the
United States for CF patients six years or older who have P.
aeruginosa present in expectorated sputum or throat swab culture
within two months prior to consent. The Cystic Fibrosis Foundation,
through its affiliate pharmacy, Cystic Fibrosis Services, Inc. is
assisting in drug distribution to treatment centers.

Patients in the U.S. with severe lung function impairment as
defined as having a FEV1 of less than 50 percent predicted or who have
completed participation in the open-label trial AIR-CF3 are eligible
to participate.

For more information regarding the expanded access program or to
request registration materials, physicians may call 1-800-490-2697 or
log on to www.EAPforCF.com.

Participating patients are evaluated at screening, at baseline, at
Day 28 and at Day 56 visits, and then every two months thereafter. In
this program, patients will receive aztreonam lysine, administered via
the PARI eFlow Electronic Nebulizer, 75 mg TID, in 56-day cycles of
therapy (28 days on drug followed by 28 days off) as provided by their
physician until patients or physicians withdraw from participation in
the study or the program is terminated by Gilead.

About Aztreonam Lysine for Inhalation

Aztreonam lysine for inhalation is an antibiotic candidate
currently being studied in Phase III clinical trials as a treatment
for people with CF who have pulmonary P. aeruginosa. Aztreonam has
potent activity against gram-negative bacteria such as P. aeruginosa.
Aztreonam formulated with arginine is a FDA-approved agent for
intravenous administration. Aztreonam lysine for inhalation is a
proprietary inhaled formulation of aztreonam and has been designated
with orphan drug status in the United States and Europe.

About PARI and the eFlow Electronic Nebulizer

Aztreonam lysine for inhalation is delivered by a novel inhalation
device, the eFlow Electronic Nebulizer, developed by PARI Pharma GmbH.
eFlow is a quiet, portable nebulizer that enables efficient
aerosolization of liquid medications via a vibrating, perforated
membrane. PARI Pharma also contributed to the development and
optimization of the drug formulation (aztreonam lysine for inhalation)
for delivery via eFlow. Based on PARI's 100-year history working with
aerosols, PARI Pharma is dedicated to advancing inhalation therapies
by developing innovative delivery platforms and new pharmaceutical
formulations that work together to improve patient care.

About Cystic Fibrosis

Today, more than 30,000 people in the United States have CF. CF is
a chronic, debilitating genetic disease. A major characteristic of CF
is production of abnormally thick, sticky mucus in the lungs that
traps bacteria and predisposes patients to lung infections, which
continually damage their lungs. Pulmonary infection with Gram-negative
bacteria, particularly pulmonary P. aeruginosa, represents the single
greatest cause of morbidity and mortality among CF patients. Currently
there is no known cure for CF, and the goal of CF therapy is to
control symptoms and prevent further lung damage.

About NACFC

Organized and funded by the Cystic Fibrosis Foundation, the North
American Cystic Fibrosis Conference is the largest CF meeting of its
kind in the world. More than 3,000 scientists and caregivers come
together each year to share the latest research and help
accelerate progress being made in the field of cystic fibrosis. For
more information on the CF Foundation, visit www.cff.org.

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 additional data from clinical studies may not warrant
further development of aztreonam lysine for inhalation for the
treatment of CF. 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 Quarterly Reports on Form 10-Q for the first
and second quarters of 2007, 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.

For more information on Gilead, please call the Gilead Public
Affairs Department at 1-800-GILEAD-5 (1-800-445-3235) or visit
www.gilead.com.