Health insurer UnitedHealth Group Inc <UNH.N> on Tuesday named its board member and former GlaxoSmithKline Plc <GSK.L> head Andrew Witty as chief executive of its pharmacy benefit unit, Optum ...

Andrew Witty, who takes over as chief executive of GlaxoSmithKline Plc <GSK.L> on May 22 in the year's biggest scheduled British corporate handover, faces a daunting task.