Increased plasma levels w/ potent CYP3A4 inhibitors (eg, ketoconazole, itraconazole, voriconazole, posaconazole, clarithromycin, telithromycin, nefazodone & HIV PIs). Weakened or inhibited effect w/ β-blockers. Prolonged QTc-interval & increased risk of ventricular arrhythmias w/ quinidine, disopyramide, procainamide, phenothiazines, terfenadine, TCAs. Impaired cardiac tolerance towards β2
sympathomimetics w/ levodopa, L-thyroxine, oxytocin, alcohol. Risk of hypertensive reactions w/ MAOIs, furazolidone & procarbazine. Elevated risk of arrhythmias w/ anaesth. Potential additive effect w/ other β-adrenergic drugs or anticholinergic drugs. Increased disposition to arrhythmias due to hypokalaemia w/ digitalis glycosides. Risk of hypokalaemia w/ xanthine derivatives, corticosteroids & diuretics.