Effects of Other Medication on VIAGRA Sildenafil metabolism is principally mediated by CYP3A4 (major route) and CYP2C9 (insignificant route). For that reason, inhibitors of these isoenzymes may decrease sildenafil clearance and inducers of such isoenzymes might raise sildenafil clearance.Sildenafil can lessen blood circulation for the optic nerve o