Voxilaprevir is a Direct-Acting Antiviral (DAA) medication used as part of combination therapy to treat chronic Hepatitis C, an infectious liver disease caused by infection with Hepatitis C Virus (HCV). Sofosbuvir/velpatasvir/voxilaprevir (Vosevi) is indicated for adult patients with chronic HCV without cirrhosis or with compensated cirrhosis who have (1) genotype 1 through 6 and have previously been treated with an NS5A inhibitor or (2) genotype 1a or 3 and have previously been treated with sofosbuvir without an NS5A inhibitor. Voxilaprevir exerts its antiviral action by reversibley binding and inhibiting the NS3/4A serine protease of Hepatitis C Virus (HCV). Following viral replication of HCV genetic material and translation into a single polypeptide, Nonstructural Protein 3 (NS3) and its activating cofactor Nonstructural Protein 4A (NS4A) are responsible for cleaving genetic material into the following structural and nonstructural proteins required for assembly into mature virus: NS3, NS4A, NS4B, NS5A, and NS5B. By inhibiting viral protease NS3/4A, voxilaprevir therefore prevents viral replication and function.

Velpatasvir (VEL; GS-5816) is an inhibitor of HCV NS5A protein, it demonstrated favourable in vitro and in vivo properties, including potent antiviral activity against hepatitis C virus genotypes 1 to 6 replicon, good metabolic stability, low systemic clearance, and adequate bioavailability and physicochemical properties to warrant clinical evaluation. Velpatasvir is used together with sofosbuvir in the treatment of hepatitis C infection of all six major genotypes. A once-daily, single-tablet, pangenotypic regimen comprising the HCV NS5B polymerase inhibitor sofosbuvir and the HCV NS5A inhibitor velpatasvir (sofosbuvir/ velpatasvir; Epclusa) has recently been approved for the treatment of adults with chronic HCV genotype 1, 2, 3, 4, 5 or 6 infection in the USA, EU and Canada.

Ledipasvir is an inhibitor of the Hepatitis C Virus (HCV) NS5A protein required for viral RNA replication and assembly of HCV virions. Approved in October 2014 by the FDA, ledipasvir and sofosbuvir (tradename Harvoni) are direct-acting antiviral agents indicated for the treatment of HCV genotype 1 with or without cirrhosis.

GS-9851 (formerly PSI 7851) is an orally available, second generation uridine nucleoside analog polymerase inhibitor of hepatitis C treatment. GS-9851 is a nucleotide prodrug of the nucleoside analog GS-331007 (formerly PSI-6206). GS-9851 potently inhibits HCV NS5B polymerase and has demonstrated pan-genotypic activity in vitro. Preclinical studies of GS-9851 demonstrated a favorable profile in terms of antiviral potency, distribution, and metabolism. GS-9851 is first hydrolyzed to the intermediate GS-566500 (formerly PSI-352707), which is then metabolized to either the inactive metabolite, GS-331007, or the monophosphate GS-606965 (formerly PSI-7411). Inside the hepatocyte, GS-606965 is further phosphorylated by a series of enzymatic steps to an active triphosphate metabolite, GS-461203 (formerly PSI-7409), that selectively inhibits recombinant NS5B. A first-time-in-human study demonstrated that GS-9851 (25 to 800 mg) is generally safe and well tolerated in patients chronically infected with HCV. GS-9851 has a pharmacokinetic profile consistent with once-daily dosing. Administration of GS-9851 led to significant reductions in plasma HCV RNA levels without the evolution of known resistance mutations.