Effects of Other Prescription drugs on VIAGRA Sildenafil metabolism is principally mediated by CYP3A4 (big route) and CYP2C9 (slight route). Consequently, inhibitors of those isoenzymes might cut down sildenafil clearance and inducers of such isoenzymes may well raise sildenafil clearance.Sildenafil works by blocking an enzyme in the human body ref