FDA approval for Merck & Co. Inc.'s once-daily hepatitis C virus (HCV) treatment, Zepatier (elbasvir and grazoprevir), is expected to bring new, but not disruptive, competition to the hot market currently dominated by Gilead Sciences Inc. Zepatier, projected by consensus forecasts to generate $544 million for Merck this year and more than twice that by 2018, according to Thomson Reuters Cortellis, offers a new oral treatment option for patients with genotype 1 and 4 infections (GT1 and GT4).