Sofosbuviris a drug used for hepatitis C virus (HCV) infection, with a high cure rate. It inhibits the RNA polymerase that the hepatitis C virus uses to replicate its RNA. Sofosbuvir is a component of the first all-oral, interferon-free regimen approved for treating chronic hepatitis C. Sofosbuvir is a prodrug that is metabolized to the active antiviral agent 2'-deoxy-2'-α-fluoro-β-C-methyluridine-5'-triphosphate. The triphosphate serves as a defective substrate for the NS5B protein, which is the viral RNA polymerase, and thus acts as an inhibitor of viral RNA synthesis. Prior to the discovery of sofosbuvir, a variety of nucleoside analogs had been examined as anti-hepatitis C treatments, but these exhibited relatively low potency. This low potency arises in part because the enzymatic addition of the first of the three phosphate groups of the triphosphate is slow.
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