Negative effect on contractility & AV conduction w/ verapamil- or diltiazem-type Ca antagonists. Potentiated atrial conduction time & -ve inotropic effect w/ class I antiarrhythmics eg, amiodarone. Reduced heart rate & cardiac output, vasodilation w/ centrally-acting antihypertensives eg, clonidine, guanfacin, moxonidine, methyldopa, rilmenidine. Increased AV conduction time w/ digitalis glycosides. Attenuated reflex tachycardia & increased risk of hypotension by anaesth. Increased fall in BP w/ baclofen, amifostine. Increased risk of hypotension w/ dihydropyridine-type Ca antagonists eg, amlodipine, felodipine, lacidipine, nifedipine, nicardipine, nimodipine, nitrendipine. Counteracted effect w/ sympathicomimetic agents. Unopposed α-adrenergic activity of sympathicomimetic agents. Increased BP-lowering effect w/ TCA, barbiturates, phenothiazines. Serotonin reuptake inhibitors, dextromethorphan, other CYP2D6-metabolised compds.
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