SEATTLE, Nov. 29, 1995 -- The U.S. Food and Drug Administration (FDA) has granted Immunex Corporation (Nasdaq: IMNX) marketing clearance for Leukine(R)(sargramostim), yeast-derived GM-CSF, for use following allogeneic bone marrow transplantation from HLA- matched related donors. In this setting, Leukine was found not only to shorten the time to white blood cell recovery but also to decrease the overall incidence of infection and the length of hospital stays.

"FDA's approval of Leukine for use in allogeneic bone marrow transplant patients highlights Leukine's infection-protecting ability for cancer patients who are at risk," said Peggy Phillips, senior vice president of pharmaceutical development for Immunex.

John Nemunaitis, M.D., director of clinical research at Texas Oncology, P.A. in Dallas, TX, was the principal investigator of the Phase III pivotal trial upon which the FDA based its approval. The results of this study were recently published in the journal Bone Marrow Transplantation.

Allogeneic Bone Marrow Transplantation

Allogeneic bone marrow transplantation (BMT) is a procedure in which the patient receives healthy bone marrow harvested from a genetically- matched donor, while autologous BMT uses the patient's own marrow. Candidates for BMT include patients with severe aplastic anemia, specific immune deficiency states, certain leukemias, resistant forms of lymphoma, and advanced or resistant solid tumors.

Following the BMT procedure, patients have reduced white blood cell counts, which puts them at great risk for infectious diseases, including pneumonia.

Data Demonstrate Leukine Protects Patients Against Infection

In a randomized, double-blind, placebo-controlled Phase III study presented to the FDA, Leukine was found to shorten the time to white blood cell count recovery, to decrease the length of hospital stay after the procedure and to reduce the overall incidence of infection. Of the patients on placebo, 75% developed infections, compared to 57% of patients receiving Leukine.

In addition, there were several secondary clinical endpoints studied, one of which was a significant reduction in severe mucositis. Mucositis is a painful condition that leads to mouth ulcers which can interfere with eating, speaking and control of saliva in addition to being a potential site of entry for infection.

In this trial, Leukine was generally well-tolerated with adverse events comparable to placebo. The most frequently reported events were fever, nausea, vomiting and diarrhea.

Leukine Holds Other New Labeling Claim

In a separate FDA action on September 15, Leukine became the first white blood cell stimulant to receive marketing clearance for use in older adults with acute myelogenous leukemia. It is the only growth factor that has been proven to prevent early death (death within 30 days of therapy) and death from infection in these patients. The drug has been indicated for autologous BMT since 1991.

Immunex is a biopharmaceutical company dedicated to developing immune system science to protect human health.

American Home Products Corporation (NYSE: AHP), through its acquisition of American Cyanamid Company, holds a majority interest in Immunex. American Home Products is one of the world's largest research based pharmaceutical and health care products companies and is a leading developer, manufacturer, and marketer of prescription drugs and over- the-counter medications. AHP is also a leader in vaccines, generic pharmaceuticals, biotechnology, agricultural products, animal health care, medical devices and food products.

CONTACT: Valoree Dowell or Robin Shapiro of Immunex, 206-587-0430 (IMNX AHP)