Oral Influenza Compound Reduced Symptoms and Prevented Illness in Humans

Phase II Data To Be Presented this Week at the 37th ICAAC in Toronto, Canada

Basel, Switzerland and Foster City, CA, USA -- September 29, 1997

F. Hoffmann-La Roche Ltd and Gilead Sciences, Inc. (NASDAQ:GILD) announced today that oral administration of the neuraminidase inhibitor GS 4104 (also known as Ro 64-0796) significantly decreased influenza viral replication and the duration of influenza symptoms when given as treatment. In addition, another Phase II study showed that GS 4104 given as prophylaxis before experimental exposure to influenza prevented illness and evidence of detectable virus. These two studies will be presented at the 37th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in Toronto, Canada.

Roche and Gilead expect to initiate the next stage of human testing, Phase II/ III studies, during the upcoming winter flu season. These treatment and prevention studies will be conducted at more than 100 clinical sites in the United States, Canada and Europe and will enroll patients naturally infected with influenza and those at risk for developing influenza illness during seasonal outbreaks.

Treatment Shortened Viral Shedding and Alleviated Flu Symptoms

In the Phase II treatment study, 80 volunteers were randomized to one of four dose levels of GS 4104 or placebo given once or twice per day for five days. Dosing was initiated 28 hours after volunteers were exposed intranasally to influenza A. GS 4104 decreased the duration of influenza symptoms by approximately 50 percent. The median time to cessation of symptoms in treated patients was 53 hours versus 95 hours in the placebo group. Twenty-four hours after treatment was initiated, the influenza viral titers were reduced by more than a hundred fold compared to placebo. These results are statistically significant.

Prophylactic Use Prevented Illness

In a Phase II prevention study, 37 volunteers were randomized to one of two dose levels of GS 4104 or placebo given once or twice per day for five days. Twenty- six hours after dosing began, volunteers were exposed intranasally to influenza A. None of the treated patients had detectable virus in nasal passages versus 50 percent in the placebo group.

Both the treatment and prevention studies were double-blind and placebo-controlled in which neither the treating physicians nor the patients knew if a patient was receiving active drug or inactive placebo. In both studies, GS 4104 was generally well tolerated, and all patients completed dosing without dose limiting side effects observed.

Active Against Both Influenza A and B

GS 4104 is the result of targeted drug design and - as an oral compound - is not only easy to administer, but also delivers active drug substance to the infection sites. The active drug substance is a potent and selective inhibitor of the influenza virus neuraminidase, an enzyme essential to the replication of influenza virus strains A and B. These strains are the major cause of flu in humans. Inhibition of neuraminidase interferes with the spread of virus from cell to cell by preventing newly formed virus from escaping from infected cells. GS 4104 is co-developed by Roche and Gilead under a collaboration agreement initiated in September 1996.

Global Need for Effective Treatment

Influenza infects an estimated 120 million people in the United States, Europe and Japan each year and is a major cause of morbidity and mortality. In periods of flu pandemics, infection rates can be even higher. Highly virulent influenza virus strains increase morbidity and mortality significantly, especially in people among high risk groups such as the elderly. Currently marketed influenza treatments, which do not target the neuraminidase enzyme, are limited due to activity only against type A strains, adverse side effect profiles and rapid development of drug-resistant virus.

F. Hoffmann-La Roche Ltd, headquartered in Basel, Switzerland, is a world leader in research-based healthcare with principal businesses in pharmaceuticals, diagnostics, vitamins, and fragrances and flavors. Roche discovers, develops and markets prescription drugs in key therapeutic areas such as virology, infectious diseases, cardiology, oncology, transplantation and metabolism.

Gilead Sciences is a biopharmaceutical company dedicated to the discovery, development and commercialization of treatments for human diseases. The Company's business and scientific endeavors are focused on making new therapies available to patients, physicians and the healthcare system. Gilead's expertise has resulted in proprietary therapeutics for important viral diseases. The Company's research programs also seek treatment options for vascular diseases and cancer. Gilead common stock is traded on The Nasdaq Stock Market under the symbol GILD.