The guanine analog Favipiravir is a broad spectrum inhibitor of viral RNA polymerase, acting on viral genetic copying to prevent its reproduction. Favipiravir is a prodrug that is metabolized to its active form, favipiravir-ribofuranosyl-5'-triphosphate (Favipiravir-RTP), which inhibits selectively RNA-dependent RNA polymerase (RdRp) in RNA viruses. This antiviral agent inhibits influenza A, B and C without inducing cytotoxicity up to 1,000 µg/ml. It also inhibits influenza strains resistant to current antiviral drugs and shows a synergistic effect in combination with oseltamivir (Prod. No. AG-CR1-3714), thereby expanding influenza treatment options. Favipiravir is active against a variety of additional viruses, including West Nile virus, yellow fever virus, foot-and-mouth disease virus as well as other flaviviruses, arenaviruses, bunyaviruses and alphaviruses in vitro and in vivo. Activity has also been shown against enteroviruses, Rift Valley fever virus and Marburg virus (MARV9), while limited efficacy has been shown against Ebola virus (EBOV) and Zika virus in animal studies. Favipiravir shows potential efficacy against SARS-CoV-2 and is undergoing clinical studies to test its efficacy and safety in the treatment of coronavirus disease 2019 (COVID-19).