Gilead Announces Achievement of Primary Efficacy Endpoint in Second Phase III Study of Aztreonam Lysine for Inhalation in Patients With Cystic Fibrosis

Gilead Sciences, Inc. (Nasdaq:GILD) today announced that its Phase
III AIR-CF1 (CP-AI-007) study of aztreonam lysine for inhalation for
the treatment of people with cystic fibrosis (CF) who have pulmonary
Pseudomonas aeruginosa (P. aeruginosa) met its primary efficacy
endpoint of change at Day 28 from baseline in respiratory symptoms, as
assessed by the Cystic Fibrosis Questionnaire-Revised (CFQ-R), a
patient-reported outcome (PRO) tool used to measure health-related
quality of life for people with CF. Data from the 164-patient,
double-blinded, randomized study demonstrated a significant
improvement in the CFQ-R, with a treatment difference in mean change
from baseline of 9.7 points in the respiratory domain (on a scale of
100) compared to placebo (p less than 0.001) following a 28-day
treatment course with 75 mg aztreonam lysine for inhalation or
volume-matched placebo administered three times daily by the PARI
eFlow(R) Electronic Nebulizer. Aztreonam lysine-treated patients also
experienced significant improvements at Day 28 in respiratory
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 0.001). Full study results will be
submitted for presentation at an upcoming scientific meeting.

The most common treatment-emergent adverse events in this study
were cough, productive cough, nasal congestion, sore throat and
dyspnea (shortness of breath). The incidences of these events were not
significantly different between the placebo and the aztreonam lysine
groups.

"The FDA, Cystic Fibrosis Foundation and medical community have
identified PROs as important endpoints in clinical trials for CF and a
variety of other diseases," said A. Bruce Montgomery, MD, Senior Vice
President, Head of Respiratory Therapeutics, Gilead Sciences. "AIR-CF1
is the first Phase III clinical trial in CF to use a PRO as its
primary endpoint. We appreciate the collaboration with regulatory
authorities and with the CF research community in designing this study
and we thank the patients and investigators for their participation.
Based on the successful completion of our second pivotal study, we
plan 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."

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

About AIR-CF Phase III Clinical Program

AIR-CF1 is one of three Phase III studies in the AIR-CF clinical
program. The program, which also includes AIR-CF2 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-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 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.

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).

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 granted
orphan drug designation in the United States and Europe.

About PARI Pharma 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, 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. 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 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. If and when regulatory approval is obtained,
we will rely on PARI to distribute the device through specialty
pharmacies or other distribution channels. If sufficient quantities of
this device are not available at the time of a commercial launch or
following such a launch, the commercial launch of aztreonam lysine for
inhalation could be delayed, and the anticipated contribution of
aztreonam lysine for inhalation to our financial results could be
adversely affected. 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 Quarterly 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.