Favikast 400 Tablets FAVIKAST-400 contains Favipiravir, a prodrug that undergoes intracellular phosphoribosylation to form its active metabolite, favipiravir ribofuranosyl 5'-triphosphate (favipiravir-RTP). Favipiravir-RTP selectively inhibits viral RNA-dependent RNA polymerase (RdRp) by acting as a purine nucleoside analogue, leading to premature termination of viral RNA synthesis or lethal mutagenesis. Because host cell DNA polymerases are not inhibited, favipiravir exhibits selective activity against broad-spectrum RNA viruses. FAVIKAST-400 is indicated for the treatment of mild-to-moderate viral infections caused by susceptible RNA viruses, including influenza and novel or re-emerging influenza virus infections.