In a move Merck & Co. Inc. chairman and CEO Kenneth C. Frazier took pains to explain as “creating greater efficiencies,” the pharma giant acceded to calls from analysts and investors to remake its R&D operation, disclosing the elimination of another 8,500 positions, in addition to previously reported reductions of 7,500 jobs, with a goal of paring annual operating expenses by approximately $2.5 billion by the end of 2015.