Merck & Co. Inc. MRK announced positive results from a comparative phase III study – C-EDGE Head-to-Head – on its hepatitis C virus (HCV) drug, Zepatier (50mg/100mg tablets), a combination product containing elbasvir and grazoprevir.The randomized, open-label, parallel-group study evaluated the safety and efficacy of Zepatier in comparison to a regimen of Gilead Sciences Inc.’s GILD Sovaldi (sofosbuvir: 400mg tablets) plus peginterferon and ribavirin (pegIFN/RBV) in treatment-naïve and pegIFN/RBV treatment-experienced patients with chronic HCV genotype (GT) 1 or GT4 infection.Data from the study showed that Zepatier was superior to the regimen of Sovaldi plus pegIFN/RBV on both the efficacy and safety endpoints.We note that in Jan 2016, Zepatier was approved in the U.S. as once-daily, fixed-dose combination tablet, indicated with or without RBV, for the treatment of chronic HCV GT1 or GT4 infection in adults. The drug is currently under review in the EU.Zepatier enjoys two Breakthrough Therapy designations in the U.S. for chronic HCV GT1 patients with end-stage renal disease on hemodialysis and for chronic HCV GT4 patients.Meanwhile, Merck has announced that a supplemental Biologics License Application for its anti-PD-1 therapy, Keytruda, has been accepted for review in the U.S. for the treatment of patients with recurrent or metastatic head and neck squamous cell carcinoma with disease progression on or after platinum-containing chemotherapy. The company is seeking to get Keytruda approved as a single agent at a dose of 200 mg administered intravenously every three weeks. The FDA has granted Priority Review with an action date of Aug 9, 2016. The application will be reviewed under the agency’s Accelerated Approval program.We remind investors that Keytruda is currently approved in the U.S. for the treatment of patients with unresectable or metastatic melanoma. It is also approved for the treatment of metastatic non-small cell lung cancer in patients whose tumors express PD-L1, as determined by an FDA-approved test, with disease progression on or after platinum-containing chemotherapy. The drug is administered at a dose of 2 mg/kg as an intravenous infusion over 30 minutes every three weeks in both the indications.In 2015, Keytruda sales came in at $566 million, up significantly from $55 million in 2014.Merck is a Zacks Rank #3 (Hold) stock. A couple of better-ranked stocks in the health care sector are AMAG Pharmaceuticals, Inc. AMAG and Emergent BioSolutions, Inc. EBS, both sporting a Zacks Rank #1 (Strong Buy).Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report MERCK & CO INC (MRK): Free Stock Analysis Report AMAG PHARMA INC (AMAG): Free Stock Analysis Report GILEAD SCIENCES (GILD): Free Stock Analysis Report EMERGENT BIOSOL (EBS): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research