Outcomes of Other Drugs on VIAGRA Sildenafil metabolism is principally mediated by CYP3A4 (big route) and CYP2C9 (minimal route). As a result, inhibitors of these isoenzymes may lower sildenafil clearance and inducers of those isoenzymes might improve sildenafil clearance.Sildenafil works by blocking an enzyme in the body known as PDE5, which helps