Briefing documents the FDA released ahead of Thursday's Antimicrobial Drugs Advisory Committee meeting on Merck & Co. Inc.'s bezlotoxumab hint at the challenges in developing new antimicrobials. Medarex, now part of Bristol-Myers Squibb Co., developed the fully human monoclonal IgG1/kappa antibody and filed the first investigational new drug application for the biologic in 2005.