May potentiate effect on AV conduction time & increase -ve inotropic effect w/ class I anti-arrhythmics (quinidine, hydroquinidine, cibenzoline, flecainide, disopyramide, lidocaine, mexiletine, propafenone). -ve influence on contractility & AV conduction w/ Ca-channel antagonists of verapamil/diltiazem type. Decrease in central sympathetic tonus (reduction of heart rate & cardiac output, vasodilation) w/ centrally-acting hypertensives (clonidine, guanfacine, monoxidine, methyldopa, rilmenidine). May potentiate effect on AV conduction w/ amiodarone. May attenuate reflex tachycardia & increase risk of hypotension w/ anaesth (volatile halogenated). May mark certain symptoms of hypoglycemia (palpitations, tachycardia) w/ insulin & oral antidiabetic drugs. Increased fall in BP w/ baclofen & amisfostine. May increase AV conduction time w/ digitalis glycosides. May increase risk of hypotension & further deterioration of ventricular pump fraction w/ Ca antagonists of dihydropyridine type (amlodipine, felodipine, lacidipine, nifedipine, nicardipine, nimodipine, nitrendipine). Enhanced hypotensive effect (additive effect) w/ antipsychotics & antidepressants (tricyclics, barbiturates & phenothiazines). May counteract effect w/ sympathomimetic agents. Increased plasma levels associated w/ increased risk of excessive bradycardia & adverse events w/ CYP2D6 isoenzyme inhibitors eg, paroxetine, fluoxetine, thioridazine & quinidine. Increased plasma levels w/ cimetidine.