2'-O-Methylcytidine -d 3 is deuterium labeled 2'-O-Methylcytidine. 2'-O-Methylcytidine is a 2'-substituted nucleoside as a inhibitor of HCV replication. 2'-O-Methylcytidine inhibits RNA-dependent RNA polymerase (NS5B)-catalyzed RNA synthesis in vitro, in a manner that is competitive with substrate nucleoside triphosphate.