are allergic to sildenafil, as contained in VIAGRA and Revatio®, or any with the substances in VIAGRAEffects of Other Medicine on VIAGRA Sildenafil metabolism is principally mediated by CYP3A4 (big route) and CYP2C9 (slight route). Consequently, inhibitors of these isoenzymes may perhaps decrease sildenafil clearance and inducers of such isoenzyme