Mark McClellan, the administrator of the Centers for Medicare & Medicaid Services, Tuesday said he plans to resign from the position.

McClellan, who has been at the post for nearly two and a half years, after two years as head of the U.S. Food and Drug Administration, said he plans to leave the agency in five weeks. He likely will take a position at a think tank where he will concentrate on ways to improve the United States healthcare system, according to an Associated Press report. The White House has not named a successor. Potential nominees include: CMS Deputy Administrator Leslie Norwalk and Herb Kuhn, director of the Center for Medicare Management at CMS.

The American Association of Homes and Services for the Aging Tuesday praised McClellan for the successful implementation of the Medicare Modernization Act of 2003, and his support for nursing home quality and the broader continuum of care.