A high dose of the late-stage migraine prevention therapy erenumab (AMG 334), co-developed by Amgen Inc. and Novartis AG, trimmed about two more migraine days than placebo from an average 8.3 monthly migraine days experienced by patients during the last three months of a confirmatory phase III trial. A low dose of the antibody bested placebo by a lesser 1.4 days. Safety was comparable to placebo, Amgen said.