May potentiate AV conduction time effect & increased negative inotropic effect w/ class I antiarrhythmics (eg, quinidine, disopyramide; lidocaine, phenytoin; flecainide, propafenone). May potentiate AV conduction time effect w/ class III antiarrhythmics (eg, amiodarone). May lead to profound hypotension & AV block w/ IV verapamil. May increase risk of rebound HTN in abrupt w/drawal of centrally-acting antihypertensives eg, clonidine & others (eg, methyldopa, moxonodine, rilmenidine). May increase risk of hypotension w/ Ca antagonists of the dihydropyridine type eg, felodipine & amlodipine; TCAs, barbiturates, phenothiazines. May add to the systemic effects w/ topical β-blocking agents (eg, eye drops for glaucoma treatment). May increase AV conduction time & risk of bradycardia w/ parasympathomimetics. Increased blood sugar lowering effect & may mask symptoms of hypoglycemia w/ insulin & oral antidiabetics. Attenuate reflex tachycardia & increase risk of hypotension w/ anaesth. Reduced heart rate & increase AV conduction time w/ digitalis glycosides. May reduce hypotensive effect w/ NSAIDs. Combination w/ β-sympathomimetics (eg, isoprenaline, dobutamine) may reduce effect of both agents. May unmask the α-adrenoceptor-mediated vasoconstrictor effects of sympathomimetics that activate both β- & α-adrenoceptors (eg, noradrenaline, adrenaline). Increased risk of bradycardia w/ mefloquine. Enhanced hypotensive effect & risk for hypertensive crisis w/ MAOIs (except MAO-B inhibitors). Slight t½
reduction w/ rifampicin. Exacerbation of peripheral circulatory disturbances w/ ergotamine derivatives.