Gilead Announces Presentation of Positive Phase III Data on Aztreonam Lysine for Inhalation in Patients With Cystic Fibrosis

Gilead Sciences, Inc. (Nasdaq:GILD) today announced detailed
results of its Phase III AIR-CF2 study evaluating aztreonam lysine for
inhalation, an antibiotic, in patients with cystic fibrosis (CF) who
have pulmonary Pseudomonas aeruginosa (P. aeruginosa). In the study, a
28-day treatment course of aztreonam lysine significantly improved the
time to need for inhaled or intravenous (IV) antibiotics versus
placebo. All patients received an initial 28 days of treatment with
tobramycin inhalation solution prior to receiving study drug.
Aztreonam lysine for inhalation was well tolerated and patients also
experienced significant improvements in pulmonary function and
respiratory symptoms. The data were presented by Karen S. McCoy, MD,
Chief of the Division of Pediatric Pulmonology and Associate Professor
of Pediatrics at The Ohio State University College of Medicine and
Chief of the Section of Pulmonology at Columbus Children's Hospital,
at this year's Cystic Fibrosis Therapeutics Development Network
conference in Seattle, Washington. Topline results from this study
were previously announced on December 19, 2006.

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 (BID) or three times (TID) daily by
the eFlow(R) 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.

Two hundred and forty-six patients were enrolled in the study and
of those 211 were randomized to receive aztreonam lysine for
inhalation or placebo. The mean age of patients treated with blinded
study drug in the trial was 26.2 years. Participants had received more
than five courses of tobramycin inhalation solution, on average, in
the previous year (mean value = 5.33 courses). More than 85 percent of
patients were taking medication (dornase alfa) to thin mucus
secretions in the lungs and nearly 70 percent were taking oral
azithromycin. At baseline, the mean percent predicted forced
expiratory volume in one second (FEV1), a measure of lung function,
was 55.7 percent overall, and 37 percent of patients had a predicted
FEV1 less than or equal to 50 percent, indicating severe impairment of
lung function.

"Pulmonary pseudomonal infection remains the leading cause of
sickness and death in people with CF," said Dr. McCoy. "Data from the
AIR-CF2 study indicate that aztreonam lysine for inhalation may
provide broad clinical benefit, which is particularly significant
given that most patients in the study had relatively long-standing CF,
a history of frequent antibiotic use and impairment of lung function
at the start of the study."

Study Results

During the 28-day run in treatment course of tobramycin inhalation
solution, patients had an average increase in improvement in FEV1 of
less than 1 percent and no improvement in respiratory symptoms as
measured by the respiratory domain of the cystic fibrosis
questionnaire-revised (CFQ-R), a patient-reported tool used to measure
health-related quality of life for people with CF.

Treatment with aztreonam lysine for inhalation lengthened the time
to the need for inhaled or IV antibiotics -- the primary endpoint of
the study -- by a median of greater than or equal to 21 days compared
to placebo (pooled p-value=0.0070 by log rank test). Physicians
determined the need for antibiotics based on the presence of decreased
ability to exercise, increased coughing, increased production of mucus
in the lungs and/or decreased appetite, all of which are signs of
exacerbation.

Aztreonam lysine-treated patients also experienced significant
improvements from baseline in respiratory function, as measured by
relative improvement of FEV1, with an absolute difference of 6.3
percent versus placebo (p=0.0012). These results were consistent
across age groups (less than 18 years of age and greater than or equal
to 18 years of age; p=0.0378 and p=0.0132, respectively).

In addition, aztreonam lysine-treated patients experienced
significantly greater improvements in respiratory symptoms, as
measured by the respiratory domain of the CFQ-R, than placebo-treated
patients. Approximately 52 percent of aztreonam lysine for
inhalation-treated patients experienced improvements exceeding the
minimal clinically important difference in respiratory symptoms
compared to 37 percent of placebo-treated patients (p=0.0196). AIR-CF2
is the first randomized, controlled study of an aerosolized antibiotic
to include and show improvements in respiratory symptoms using the
CFQ-R questionnaire.

Aztreonam lysine for inhalation 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. Pseudomonas sensitivity as measured by minimum
inhibitory concentrations did not significantly change from baseline
to the end of therapy in aztreonam lysine for inhalation-treated
patients after 28 days of therapy.

The safety profile observed in AIR-CF2 was consistent with
expected symptoms of underlying CF lung disease. The most common
treatment-emergent adverse events were cough, productive cough, nasal
congestion, respiratory tract congestion and wheezing. The overall
rates of adverse events, drug-related adverse events and serious
adverse events were similar among patients treated with aztreonam
lysine for inhalation and those treated with placebo.

"We are very encouraged by the outcomes of this unique study,
which was designed in concert with the Cystic Fibrosis Foundation,
leading CF researchers and through a Special Protocol Assessment with
the U.S. Food and Drug Administration," said A. Bruce Montgomery, MD,
Senior Vice President, Head of Respiratory Therapeutics, Gilead
Sciences. "These comprehensive findings provide valuable insights into
the clinical profile of aztreonam lysine for inhalation. Data from
additional studies in the AIR-CF Phase III clinical program will help
to fully characterize the potential benefits and most effective use of
this agent in people living with CF who have pulmonary P. aeruginosa."

Data from this analysis have not been reviewed by the U.S. Food
and Drug Administration (FDA). Aztreonam lysine for inhalation is an
investigational treatment and has not yet been determined safe or
efficacious in humans.

About the AIR-CF Phase III Clinical Program

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

AIR-CF1 is a double-blind, randomized, placebo-controlled study
designed to assess the safety and efficacy of a 28-day treatment
course of aztreonam lysine for inhalation in people with CF who have
pulmonary P. aeruginosa. The primary endpoint is the change at day 28
from baseline in respiratory symptoms as assessed by the CFQ-R
questionnaire. This study has enrolled more than 150 patients who were
randomized to receive 28 days of treatment with 75 mg aztreonam lysine
for inhalation or volume-matched placebo administered TID by the eFlow
Electronic Nebulizer.

AIR-CF3 is an 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 for inhalation with
the same regimen they received in AIR-CF1 or AIR-CF2 (BID or TID
daily).

Gilead anticipates that data from AIR-CF1 will be available in the
second quarter of 2007 and plans to submit a New Drug Application
(NDA) for aztreonam lysine for inhalation for the treatment of people
with CF who have pulmonary P. aeruginosa to the U.S. FDA in the second
half of 2007.

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 is delivered through a novel inhalation device,
the eFlow Electronic Nebulizer, developed by PARI Pharma GmbH. The
eFlow is an electronic, portable nebulizer that enables efficient
aerosolization of liquid medications via a vibrating, perforated
membrane.

PARI is dedicated to advancing aerosol therapies through
innovative device and formulation technologies. PARI develops and
manufactures aerosol delivery systems for patients with lung diseases,
and was a partner in developing the aztreonam lysine formulation.

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, trapping
bacteria and predisposing 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 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
statements related to Gilead's ability to obtain data from AIR-CF1 and
submit an NDA for aztreonam lysine for inhalation for the treatment of
CF to the U.S. FDA as currently planned. For example, the safety and
efficacy data from additional clinical studies may not warrant further
development of this compound and initiating and completing clinical
trials may take longer or cost more than expected. 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, the U.S. FDA may not approve aztreonam
lysine for inhalation for the treatment of CF in the United States,
and any marketing approval, if granted, may have significant
limitations on its use. 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, 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.