Filitra 20 mg is generally marketed as vardenafil 20 mg, a PDE5 inhibitor. Vardenafil can interact dangerously with nitrates such as nitroglycerin or isosorbide. Both medicines can lower blood pressure by increasing blood-vessel relaxation. Taking them together can cause a sudden, potentially severe drop in blood pressure, which can lead to dizziness, fainting, or serious cardiovascular complications. Vardenafil should not be taken with nitrates, including intermittent nitrate use. Current prescribing information lists this combination as contraindicated. Do not decide on a “safe” waiting interval yourself; the prescribing information states that a suitable interval after vardenafil has not been established. If you use nitroglycerin, isosorbide mononitrate, or isosorbide dinitrate, tell your doctor or pharmacist before taking Filitra.