<p>Labetalol in combination with tricyclic antidepressants may cause tremor; Cimetidine has been shown to increase the bioavailability of Labetalol. If Labetalol is used with nitroglycerin in patients with angina pectoris, additional antihypertensive effects may occur; Care should be taken if Labetalol is used concomitantly with calcium antagonists of the verapamil type; Both digitalis glycosides and beta-blockers slow atrioventricular conduction and decrease heart rate. Concomitant use can increase the risk of bradycardia.</p>