Coadministration has not been studied. Favipiravir is mainly metabolised by aldehyde oxidase and undergoes no CYP-mediated metabolism. Favipiravir is a moderate inhibitor of OAT1. Adefovir is eliminated renally via glomerular filtration and active renal secretion by OAT1. Inhibition of this renal transporter could impair adefovir renal elimination.  Monitor renal function when coadministering these drugs.