<p><strong>Sofosbuvir</strong>&nbsp;is an inhibitor of the hepatitis C virus (HCV) NS5B ribonucleic acid (RNA)-dependent RNA polymerase, which is essential for viral replication. Sofosbuvir is a nucleotide prodrug that undergoes intracellular metabolism to form the pharmacologically active uridine analog triphosphate (GS-461203), which can be incorporated into HCV RNA by the NS5B polymerase and acts as a chain terminator. In a biochemical assay, GS-461203 inhibited the polymerase activity of the recombinant NS5B from HCV genotype 1b, 2a, 3a and 4a with a 50% inhibitory concentration (IC50) value ranging from 0.7-2.6 micrometer. GS-461203 (the active metabolite of sofosbuvir) is not an inhibitor of human deoxyribonucleic acid (DNA) and RNA polymerases, nor an inhibitor of mitochondrial RNA polymerase.<br />
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<strong>Daclatasvir</strong>&nbsp;stops HCV viral RNA replication and protein translation by directly inhibiting HCV protein NS5A. NS5A is critical for HCV viral transcription and translation.</p>