Levitra (vardenafil) is one of the three most popular drugs approved by the FDA for the treatment of erectile dysfunction. Take your Levitra about 60 minutes before you are planning to have sex. Do not take another dosage within the next 24 hours. Talk to your health care provider if you think this medicine is not working properly for you and you think you may be required to have your dosage adjusted. Do not start using Levitra if you recently took a nitrate-based drug (isosorbide dinitrate, nitroglycerin, or isosorbide mononitrate) as a drug interaction may occur. Make sure you talk to your health care provider before taking Levitra and discuss any medicines you are taking at the moment to make sure you benefit from the treatment and experience no dangerous symptoms. Make sure your health care provider knows that you are currently taking any of the following medicines: rifampin, phenytoin, diltiazem, quinidine, troleandomycin, high blood pressure or irregular heartbeat medications, rifabutin, danazol, as well as dexamethasone, lovastatin, alpha blockers, antifungals, sertraline, cyclosporine, HIV protease inhibitors, drugs for the treatment of erectile dysfunction, zafirlukast, erythromycin, phenobarbital, clarithromycin, delavirdine, cimetidine, fluvoxamine, carbamazepine, procainamide, isoniazid, fluoxetine, verapamil, nevirapine, sotalol, paroxetine, nefazodone, metronidazole, efavirenz, disopyramide. Taking any of these drugs can affect the efficiency of Levitra or render your treatment less effective.