Health care was weak due in large part to a large loss in Gilead Sciences (GILD 92.90, -15.55), which followed reports that pharmacy benefits manager Express Scripts is going to displace Gilead’s hepatitis C drug, Sovaldi, in favor of a less expensive offering from AbbVie, Viekira Pak, which recently won FDA approval and will become the exclusive option in the formulary for patients with genotype 1 hepatitis C.