Dialysis clinic chain DaVita Inc. said Monday it is responding to a federal subpoena for documents related to Medicare claims for several drugs. The subpoena is related to a previously announced investigation.

The subpoena from the Department of Health and Human Services Office of Inspector General is related to an ongoing investigation by the Department of Justice and U.S. Attorney’s Office for the Northern District of Georgia over the administration of iron and vitamin D drugs. There have been concerns over the years that the drugs were overprescribed by doctors in order to bump up Medicare reimbursements.

The subpoena requests documents from Jan. 1, 2003 to the present, and is the second in as many years to DaVita.

“We respect the government’s need to ensure the appropriateness of health care provider practices, especially during times when pharmaceutical issues involve significant expense for Medicare,” DaVita spokeswoman LeAnne Zumwalt said in a statement. No proceedings have been initiated against the company, she said, and the company, which is nation’s second-largest operator of dialysis centers, intends to cooperate fully with the government.

DaVita shares were up 13 cents, less than 1 percent, to $48.02 in morning trading on the New York Stock Exchange.