ENBREL Receives FDA Approval for Rheumatoid Arthritis

Douglas Petkus
Wyeth-Ayerst Laboratories
(610) 971-4980

ENBREL(tm) Receives FDA Approval for Treatment of Rheumatoid Arthritis

First in a New Class of Drugs is a Breakthrough

SEATTLE -- ENBREL(tm) (etanercept) received approval from the U.S. Food and Drug Administration (FDA) today, announced Immunex Corporation (NASDAQ: IMNX) and Wyeth-Ayerst Laboratories, a division of American Home Products Corporation (NYSE: AHP), the companies who will market ENBREL in North America. ENBREL is being made immediately available for distribution and can be obtained by prescription from a physician.

The first in a new class of rheumatoid arthritis (RA) drugs known as biologic response modifiers, ENBREL is an entirely new approach to management of moderate to severe RA. In clinical studies of patients with moderate to severe RA, ENBREL has been shown to reduce pain and duration of morning stiffness and improve the number of swollen and tender joints, enabling patients to better participate in daily activities.

"It's a great day for people like me who have had RA for years," said Veronica Lewandowski, an ENBREL clinical trial participant.

"ENBREL works in an entirely new way, specifically interrupting the inflammatory process in RA, in which TNF plays a key role," said Dr. Michael Franklin, an ENBREL clinical investigator and Ms. Lewandowski's rheumatologist. Dr. Franklin serves as Chief of Rheumatology, Abington Memorial Hospital, Philadelphia, Pennsylvania. "ENBREL has been shown to provide dramatic symptomatic relief, even in patients who have not been successfully treated with current options."

ENBREL is indicated for the reduction in signs and symptoms of moderately to severely active rheumatoid arthritis in patients who have an inadequate response to one or more disease-modifying anti-rheumatic drugs (DMARDs). ENBREL can be used in combination with methotrexate in patients who do not respond adequately to methotrexate alone. The dosage of ENBREL for adult patients with RA is 25 mg given twice weekly as a subcutaneous injection.

"We are proud of everyone involved in the research and development of ENBREL, and are delighted to make this milestone treatment for RA available," said Peggy V. Phillips, Immunex senior vice president, pharmaceutical development and general manager, ENBREL. "We commend officials of the Food and Drug Administration who worked tirelessly and efficiently to review and approve this innovative new therapy."

"Several hundred Wyeth-Ayerst representatives will now begin educating the RA community about ENBREL, and reaching out to health care providers and consumers nationwide with comprehensive education and service programs to make them aware of this innovative new therapy," said Joseph M. Mahady, president, Wyeth-Ayerst Pharmaceuticals, North America.

ENBREL acts by binding tumor necrosis factor (TNF). TNF is one of the dominant cytokines or proteins that play an important role in the cascade of reactions that cause the inflammatory process of RA. ENBREL competitively inhibits the binding of TNF molecules to the TNF receptor (TNFR) sites. The binding of ENBREL to TNF renders the bound TNF biologically inactive, resulting in significant reduction in inflammatory activity.

ENBREL has been studied in more than 1,000 people with RA. At 3 months, Phase III study results in 234 patients demonstrated that 62 percent of the patients receiving a 25 mg dose of ENBREL reached the primary endpoint of 20 percent improvement by ACR criteria -- a composite score of select measurements of RA symptoms including joint pain, joint swelling, and patient and physician global assessment -- compared to 23 percent of the patients in the placebo group. In this study, responses were rapid, often appearing within one to two weeks after initiation of therapy, and nearly always occurred within 3 months. At 6 months, the secondary endpoints of this study demonstrated a 69% median improvement in pain (vs. 2% for placebo), a 71% median improvement in tender joint counts (vs. 6% for placebo), a 51% median improvement in swollen joint counts (vs. 2% for placebo), and an 88% median reduction in duration of morning stiffness (vs. 4% for placebo). Phase III results!

confirmed earlier Phase II findings.

The most frequently reported adverse events in studies with ENBREL were mild to moderate injection site reactions, however, 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 of its components should not take ENBREL. If patients develop a serious or unusual infection while on ENBREL, they should talk with their doctor immediately.

Immunex and Wyeth-Ayerst Laboratories will market ENBREL in North America. Other Wyeth-Ayerst affiliates will market ENBREL outside of North America. Additional information about ENBREL, including full prescribing information, can be found on the company-sponsored web site at (www.Enbrelinfo.com) or by calling toll-free 1-888-4ENBREL (1-888-436-2735).

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.

American Home Products Corporation's Wyeth-Ayerst Laboratories division 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 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, patent litigation, product commercialization and other risks described from time to time in the SEC reports filed by Immunex, including the most recently filed 10-K and 10-Q. For more information, please refer to www.immunex.com.

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