Merck & Co. Inc., of Whitehouse Station, N.J., said grazoprevir/elbasvir, an investigational single-tablet regimen for the treatment of chronic hepatitis C virus (HCV) infection, has received two new breakthrough therapy designations from the FDA for the treatment of patients with chronic HCV genotype 4 infection, and for the treatment of chronic HCV genotype 1 (GT1) infection in patients with end-stage renal disease on hemodialysis.