Major leadership changes are under way at Covington-based Omnicare Inc., the nation’s largest provider of pharmaceutical care for the elderly. On Monday, the Fortune 500 company announced that long-time president and CEO Joel F. Gemunder retired along with senior vice president and secretary Cheryl D. Hodges over the weekend. Their departures were effective July 31. Gemunder, 71, has also retired from his post as a director. The news follows the June retirement of COO Patrick Keefe. James “Denny” Shelton, a company director and the former chairman and chief executive officer of Plano, TX-based Triad Hospitals, Inc., is replacing Gemunder on an interim basis, the company said. The search for a new CEO is expected to take up to four to five months. “We are confident that there will be many qualified candidates,” said Andy Brimmer, a company spokesman.