Potentiated effect on AV conduction time & increased -ve inotropic effect w/ class I antiarrhythmics eg, quinidine, hydroquinidine, cibenzoline, flecainide, disopyramide, lidocaine, mexiletine, propafenone. Negative influence on contractility & AV conduction w/ verapamil-/diltiazem-type Ca-channel antagonists. Profound hypotension & AV block w/ verapamil IV. Worsened heart failure w/ centrally-acting antihypertensives eg, clonidine, guanfacin, moxonidine, methyldopa, rilmenidine. Potentiated effect on AV conduction time w/ class III antiarrhythmics eg, amiodarone. Attenuated reflex tachycardia & increased risk of hypotension w/ volatile halogenated anaesth. May mask symptoms of hypoglycaemia w/ insulin & oral antidiabetic drugs. Increased BP fall w/ baclofen, amifostine. Increased risk of hypotension w/ dihydropyridine-type Ca antagonists eg, amlodipine, felodipine, lacidipine, nifedipine, nicardipine, nimodipine, nitrendipine. Enhanced hypotensive effect w/ antipsychotics, antidepressants eg, phenothiazines, tricyclics, barbiturates. Counteracted effect w/ sympathicomimetic agents. Increased plasma levels w/ paroxetine, fluoxetine, thioridazine, quinidine; cimetidine; nicardipine.