Amgen Drug Study Causes Stock to Fall $3 : Medicine: But a report of higher infection rates in a small sample of cancer patients taking the firm’s best-selling erythropoietin is largely discounted.

Amgen Inc.’s stock fell $3 Monday to close at $130 after a medical study said cancer patients had a greater risk of infection after taking the company’s best-selling biotechnology drug.

The drug is erythropoietin, or EPO, a gene-spliced version of a human protein found in the bone marrow that triggers production of red blood cells.

According to the study, nine cancer patients treated for three to four months with EPO suffered a 15% to 50% decline in their white blood cell counts. White blood cells are one of the body’s key infection fighters. The study was performed by hematologists from Georgetown University and the Walter Reed Army Institute of Research in Washington.

But David Stone, biotechnology analyst with Cowen & Co., discounted the Georgetown survey. “I think the data base is too small and the findings contrary to observations in larger numbers of patients to get very excited about.”

Jim McCamant, editor of the Medical Technology Stock Letter, said the medical study would have “a minor impact” on Amgen because the dominant market for EPO is in treating anemia in kidney disease patients, not in cancer patients.

Since Amgen won government approval in June, 1989, to sell EPO, it has become biotechnology’s best-selling drug. Red blood cells transport oxygen throughout the body, and patients with kidney disease often suffer chronic anemia and need frequent blood transfusions. But EPO restores their lost energy and usually eliminates the transfusions. In its fiscal year that ended March 31, Amgen sold $304 million worth of EPO.

Amgen officials also discounted the Georgetown study. Spokesman Mark Brand said more than 75,000 kidney patients have been treated with EPO, and only one patient showed a decline in white blood cells.

Said Stone: “There are probably 85,000 (kidney) dialysis patients on EPO continuously. If they had problems we would have heard about it.”

EPO is now being used to combat other forms of anemia, including in AIDS patients and in cancer patients undergoing chemotherapy. Amgen has a monopoly to sell EPO to kidney patients, but it has licensed the drug for other medical uses to a Johnson & Johnson subsidiary.