Special warnings, drug interactions: Levitra is not used in patients c elongated Q-T interval of the possibility of cardiac arrhythmias. Should avoid concomitant medication with nitrates (such as nitroglycerin) or alpha-adrenergic blockers cialis (drugs for the treatment of benign prostatic hyperplasia and / or lowering blood pressure), as a joint application with these drugs can lead to a drastic reduction in blood pressure and collapse. Some medicines can affect the metabolism of Levitra, in connection with the patients should consult with a doctor in case of appointment of a new drug viagra. For example, for patients taking erythromycin, the maximum dose of levitra is 5 mg, and for patients taking ritonavir, - 2,5 mg dose within 72 hours