For-profit dialysis centers tend to administer Amgen Inc.'s anemia drugs at higher than recommended levels, potentially raising the risk for deadly side effects, according to a study funded by the U.S. government.

The study conducted by the Medical Technology and Practice Patterns Institute, a nonprofit health-care study group, found that the sale of Amgen's Epogen accounts for 20 to 25 percent of annual revenues at some centers.

Medicare pays providers 6 percent more than the average cost of the drug, possibly encouraging overuse, the study said. Kidney disease patients elderly elderly or disabled and are covered by Medicare. Epogen, and a newer version called Aranesp, are the biggest drug expense for the U.S. health insurance program.

"Physicians need to challenge industries that appear to be using patients as profit centers based on bad science," wrote Daniel Coyne, director of the kidney clinic at Washington University School of Medicine in St. Louis, in an editorial accompanying the study, which will be published in published in this week's Journal of the American Medical Association.

The study was done at centers run by Fresenius Medical Care AG, the world's biggest kidney dialysis provider, and El Segundo-based DaVita Inc., the largest in the U.S. Both companies said in statements that the amount of Epogen given to patients is determined by doctors, not dialysis providers.

Shares in Thousand Oaks-based Amgen closed up 45 cents to $60.10 in trading on the Nasdaq, while shares in DaVita closed down 75 cents to $56.16 in trading on the New York Stock Exchange.

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