Potentiated AV conduction time & increased -ve inotropic effect w/ class I & III antiarrhythmic drugs (eg, quinidine, disopyramide, lidocaine, phenytoin, flecainide, propafenone, amiodarone). Increased AV conduction time w/ parasympathomimetics & digitalis glycosides. Increased risk of hypotension w/ Ca channel blockers, anesth, MAOIs & other drugs w/ BP-lowering potential (eg, TCAs, barbiturates, phenothiazide). Potential systemic effect w/ topical β-blockers. Increased blood sugar-lowering effect w/ insulin & oral antidiabetic drugs. Reduced hypotensive effect w/ NSAIDs. May reduce effect w/ β-sympathomimetics (eg, isoprenaline, dobutamine). Increased risk of bradycardia w/ mefloquine. Risk of hypertensive crisis w/ MAOIs. Reduced t½
w/ rifampicin. Exacerbation of peripheral circulatory disturbance w/ ergotamine derivatives.