Marked increase in plasma levels w/ co-administration of strong CYP3A4 inhibitors (eg, ritonavir, atazanavir, clarithromycin, indinavir, itraconazole, nelfinavir, saquinavir, ketoconazole, telithromycin). TCAs or MAOIs (during the immediate 2-wk period following discontinuation) or other drugs known to prolong QTc interval eg, antipsychotics (including phenothiazines), quinidine, disopyramide, procainamide & antihistamines. ECG changes &/or hypokalemia may occur w/ non-K-sparing diuretics. Possible hypokalemic effect w/ xanthine derivatives, glucocorticosteroids & digitalis glycosides. L-Dopa, L-thyroxine, oxytocin & alcohol may impair cardiac tolerance towards β2
-sympathomimetics. Elevated risk of arrhythmias w/ anesth w/ halogenated hydrocarbons. Additive effect w/ other β-adrenergic drugs. Concurrent administration w/ β-adrenergic receptor antagonists may inhibit effects.