Dialysis center operator DaVita Inc. said Thursday the U.S. government was seeking additional records regarding use of Amgen Inc.'s anemia drug Epogen to determine whether the drug was being over prescribed.

The Houston branch of the Office of Inspector General of the U.S. Department of Health and Human Services is seeking claims information submitted to Medicare, which spends an estimated $2 billion a year on Epogen. The red blood booster is often prescribed to fight anemia for patients whose kidneys are failing and are under regular dialysis.

DaVita said there appears to be "substantial" overlap between the Texas investigation and an ongoing review of Epogen utilization and claims by the U.S. Attorney's Office for the Eastern District of Missouri. The U.S. Attorney's Office for the Eastern District of Pennsylvania ended its own probe last month of Epogen utilization at DaVita clinics without taking action against the company.

"We have had consistently outstanding anemia management and mortality outcomes for several years and we are as comfortable talking about our practices in this area as we have been in our prior two investigations," Chief Executive Kent Thiry said in a statement.

DaVita shares were down 46 cents, or less than 1 percent, to $57.10 in midday trading on the New York Stock Exchange.

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