Increased plasma conc w/ ketoconazole, erythromycin, cimetidine. Hypertensive reactions including hypertensive crises w/ MAOIs. Reduced antihypertensive effects of methyldopa, mecamylamine, reserpine, veratum alkaloids. Increased ectopic pacemaker activity w/ digitalis. Increased absorption rate w/ antacids. Decreased absorption rate w/ kaolin. Concomitant use w/ β-blockers.