News Release

Immunex And Wyeth-Ayerst Laboratories Advance Enbrel Into Phase II/III Clinical Trial For Chronic Heart Failure

Peer-Reviewed Publication

Immunex Corporation

Positive Results of Phase I Study Presented At American College of Cardiology Conference

SEATTLE -- Immunex Corporation (NASDAQ:IMNX and Wyeth-Ayerst Laboratories announced today that they are beginning a Phase II/III clinical trial with ENBREL (etanercept) in chronic heart failure patients, one of the first large-scale studies undertaken to evaluate cytokine inhibition, an entirely new approach to studying chronic heart failure. This study will be based on positive results of a Phase I study presented today at the annual conference of the American College of Cardiology in New Orleans, LA.

Results of the double-blind, randomized, placebo-controlled multi-dose Phase I safety study in 47 heart failure patients demonstrated that ENBREL was well tolerated. The incidence of adverse events was similar in all treatment groups. The study was conducted by Dr. Douglas Mann and Dr. Guillermo Torre at Baylor College of Medicine, and Dr. Arthur M. Feldman at University of Pittsburgh Medical Center.

The 47 patients were New York Health Assessment (NYHA) class III-IV and were randomized to be treated for three months with twice weekly injections of either ENBREL at 5mg/m2, 12mg/m2 or placebo. At three months, measurements of clinical activity suggested consistent improvement for patients on ENBREL in NYHA classification, left ventricular ejection fraction, quality of life, and in a clinical composite score. In addition, there appeared to be a positive dose response in each of the categories above. Based on the results of the study, and additional clinical and preclinical data associating elevated TNF levels with chronic heart failure, the two companies have elected to proceed to a Phase II/III multicenter trial.

"We are pleased that the results of the multidose Phase I study supported moving into a Phase II/III multicenter trial," said Peggy Phillips, senior vice president of pharmaceutical development and general manager, ENBREL at Immunex. "ENBREL is one of our lead development products and we continue to evaluate its potential role in a variety of disease states."

"These initial findings represent the first step in our research program for ENBREL in heart failure," said L. Patrick Gage, president, Wyeth-Ayerst Research. "As the clinical development program for chronic heart failure evolves, patients and physicians can look forward to additional information from this novel research."

The new, double-blind, placebo controlled study, named the RENAISSANCE trial (Randomized ENBREL North American Strategy to Study Antagonism of Cytokines), will be conducted in multiple sites in North America and will involve 900 patients with heart failure who are NYHA class II-IV (moderate to severe). A companion trial named RECOVER (Research into ENBREL: Cytokine Antagonism in Ventricular Dysfunction) will be conducted in Europe and Australia by Wyeth-Ayerst Global Pharmaceuticals.

The Role of TNF in Chronic Heart Failure

Research has shown that tumor necrosis factor (TNF), an immune system protein is present in increased amounts in damaged heart tissue. TNF exerts its effects by interacting with specific TNF receptors that are on the surface of cells. When TNF binds with TNF receptors, it sets off a chain of events within the cell that may lead to further damage to the heart.

ENBREL is a genetically engineered soluble receptor that works by binding to TNF and preventing it from interacting with cell surface receptors that are on the cells in the heart and circulatory system.

Nearly 5 million Americans have chronic heart failure today. Of these, about 1.5 million have NYHA class III-IV chronic heart failure. Chronic heart failure is one form of heart disease that results when the heart is damaged from diseases such as high blood pressure, a heart attack, poor blood supply to the heart, a defective heart valve, atherosclerosis, rheumatic fever or heart muscle disease. The failing heart keeps working, but becomes inefficient, resulting in fluid retention and shortness of breath, fatigue and exercise intolerance. The condition often progresses and becomes irreversible.

ENBREL has been approved by the U.S. Food and Drug Administration for the reduction in signs and symptoms of moderately to severely active rheumatoid arthritis (RA) in patients who have an inadequate response to one or more disease modifying anti-rheumatic drugs. The most frequently reported adverse events in RA studies with ENBREL in adults were mild to moderate injection site reactions. The long-term effects of ENBREL treatment on the development or course of serious infection, malignancy and autoimmune disease are unknown. Patients with a serious infection, including sepsis, or who are allergic to ENBREL or any to its components should not take ENBREL. If patients develop a serious or unusual infection while on ENBREL, they should talk with their doctor immediately. Full prescribing information for ENBREL is available by calling 1-800-IMMUNEX or by visiting www.enbrelinfo.com.

Immunex is a biopharmaceutical company dedicated to developing immune system science to protect human health. The company's products offer hope to patients with cancer, inflammatory and infectious diseases.

Wyeth-Ayerst Laboratories, a division of American Home Products Corporation, is a major research-oriented pharmaceutical company with leading products in the areas of women's health care, cardiovascular disease therapies, central nervous system drugs, anti-inflammatory agents, vaccines and generic pharmaceuticals.

American Home Products owns a majority interest in Immunex. AHP is one of the world's largest research-based pharmaceutical and health care products companies. It is a leader in the discovery, development, manufacturing and marketing of prescription drugs and over-the-counter medications. It is also a global leader in vaccines, biotechnology, agricultural products, and animal health care.

NOTE: This news release contains forward-looking statements that involve risks and uncertainties, including risks associated with clinical development, regulatory approvals, product commercialization and other risks described from time to time in the SEC reports filed by Immunex, including the most recently filed Form 10K and 10-Q.

CONTACT:
Pam Rabe (media)(206) 470-4131
Mark Leahy (investors)(206) 389-4363

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