Effects of Other Medications on VIAGRA Sildenafil metabolism is principally mediated by CYP3A4 (major route) and CYP2C9 (small route). Hence, inhibitors of those isoenzymes could minimize sildenafil clearance and inducers of such isoenzymes might raise sildenafil clearance.Sildenafil functions by blocking an enzyme in the body called PDE5, which al