Avanafilmetabolite M16 is a major inactive metabolite of the phosphodiesterase 5 (PDE5) inhibitor avanafil . Avanafil is metabolized by the cytochrome P450 (CYP450) isoforms CYP3A4 and CYP2C to the major metabolites avanafilmetabolite M16 and avanafilmetabolite M4 , as well as minor metabolites.