Florida Gov. Charlie Crist has appointed Thomas W. Arnold as secretary of the Agency for Health Care Administration, which oversees the state's $18 billion Medicaid program. Arnold, 60, who had been serving as AHCA's chief of staff since 2008, replaces Holly Benson, who resigned. Arnold has spent his career in public health administration. He was the state Medicaid director with AHCA from 2004 to 2007. He also served in the Florida Department of Health as deputy state health officer in 2008, deputy secretary from 2003 to 2004 and director of administration from 1998 to 2003.