Merck & Co. Inc., of Boston, said results from a phase II trial, dubbed C-Worthy, testing grazoprevir/elbasvir (MK-5172/MK-8742, the company's investigational NS3/4A protease inhibitor and NS5A inhibitor, respectively) with or without ribavirin (RBV) in treatment-naïve and previously treated (with peg-interferon/ribavirin) patients with chronic hepatitis C virus (HCV) genotype 1 (GT1) infection showed rates of sustained viral response 12 weeks after the completion of therapy (SVR12) greater than, or equal to 90 percent regardless of treatment duration or co-administration of RBV.