PSI-7977 is a prodrug that is metabolized to the active antiviral agent 2'-deoxy-2'-a-fluoro-B-C-methyluridine-5'-monophosphate and is currently being investigated in phase 3 clinical trials for the treatment of hepatitis C. Studies have profiled PSI-7977 as a nucleotide inhibitor of hepatitis C virus, exerting selective inhibitory effects towards HCV NS5B polymerase.