Favipiravir (T-705; 6-fluoro-3-hydroxy-2-pyrazinecarboxamide) is an anti-viral 
agent that selectively and potently inhibits the RNA-dependent RNA polymerase 
(RdRp) of RNA viruses. Favipiravir was discovered through screening chemical 
library for anti-viral activity against the influenza virus by Toyama Chemical 
Co., Ltd. Favipiravir undergoes an intracellular phosphoribosylation to be an 
active form, favipiravir-RTP (favipiravir ribofuranosyl-5'-triphosphate), which 
is recognized as a substrate by RdRp, and inhibits the RNA polymerase activity. 
Since the catalytic domain of RdRp is conserved among various types of RNA 
viruses, this mechanism of action underpins a broader spectrum of anti-viral 
activities of favipiravir. Favipiravir is effective against a wide range of 
types and subtypes of influenza viruses, including strains resistant to existing 
anti-influenza drugs. Of note is that favipiravir shows anti-viral activities 
against other RNA viruses such as arenaviruses, bunyaviruses and filoviruses, 
all of which are known to cause fatal hemorrhagic fever. These unique anti-viral 
profiles will make favipiravir a potentially promising drug for specifically 
untreatable RNA viral infections.