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

AIR-CF1 is First Phase III Clinical Trial in Cystic Fibrosis to Evaluate Patient-Reported Outcomes (PROs) as a Primary Endpoint

FOSTER CITY, CA, MAY 29, 2007 -- 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<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® Electronic Nebulizer.

Aztreonam lysinetreated 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<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 andinvestigators 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.