By Ransdell Pierson -- NEW YORK, July 13 (Reuters) - Merck & Co. Inc. (MRK.N: Quote, Profile, Research) said on Thursday that the head of its U.S. drug operations, Bradley Sheares, has left the drug maker. A spokesman for Merck said employees had been informed in an internal memorandum that Sheares, who several years ago had been considered a leading candidate to become Merck’s chief executive officer, was no longer working for the U.S. company.
