Potentiated effect on AV conduction time & increased -ve inotropic effect w/ class IA antiarrhythmic drugs (eg, quinidine, disopyramide, lidocaine, phenytoin, flecainide, propafenone). Profound hypotension & AV block w/ IV administration of verapamil. Decrease the central sympathetic tonus & thus lead to the reduction of heart rate & cardiac output & vasodilatation w/ concomitant use of centrally-acting antihypertensive drugs (eg, clonidine, methyldopa, moxonidine, rilmenidine). Increased risk of hypotension w/ concomitant use of Ca antagonists of dihydropyridine type (eg, felodipine & amlodipine) & other drugs w/ BP-lowering potential (eg, TCAs, barbiturates, phenothiazines). Potentiated effect on AV conduction time w/ class III antiarrhythmic drugs (eg, amiodarone). Added systemic effects w/ topical β-blockers (eg, eye drops for glaucoma treatment). Increased effect on AV conduction time & risk of bradycardia w/ parasympathomimetic drugs, cardiac glycosides (digitalis). Increased blood-sugar lowering effect of insulin or oral antidiabetic drugs. Attenuation of the reflex tachycardia & increased risk of hypotension w/ anesth agents. Reduced hypotensive effect w/ NSAIDs. Reduced effect of β-sympathomimetics (eg, isoprenaline, dobutamine). Increased BP & exacerbated intermittent claudication w/ non-selective β-blockers (eg, norepinephrine, epinephrine). Increased risk of bradycardia w/ mefloquine. Risk for hypertensive crisis w/ MAOIs (except MAO-B inhibitors). Slight reduction of t½
w/ rifampicin. Exacerbation of peripheral circulatory disturbances w/ ergotamine derivatives.