Favipiravir was originally developed by Fujifilm group, Japan. It is a pyrazine-carboxamide derivative (Figure 4) with a broad-spectrum antiviral activity. It selectively and potently inhibits the RdRp of RNA viruses [69]. Favipiravir is a prodrug that requires bioactivation in host-infected cells. Its active form is favipiravir-ribose-5′-triphosphate. The first step in the formation of the active species is potentially catalyzed by human hypoxanthine guanine phosphoribosyl-transferase [70], which converts favipiravir into ribose-5′-monophosphate intermediate. The latter intermediate undergoes two phosphorylation steps mediated by the action of host kinases leading to the formation of the ribose-5′-triphosphate active form.