Plasma levels of budesonide may be markedly increase w/ potent CYP3A4 inhibitors eg, ketoconazole, itraconazole, voriconazole, posaconazole, clarithromycin, telithromycin, nefazodone & HIV PIs. Weakened or inhibited effect of formoterol w/ β
2-adrenergic blockers (including eye drops). Prolonged QTc-interval & increased risk of ventricular arrhythmias w/ quinidine, disopyramide, procainamide, phenothiazines, antihistamines (terfenadine) & TCAs. Impaired cardiac tolerance towards β
2-sympathomimetics w/ L-dopa, L-thyroxine, oxytocin & alcohol. May precipitate hypertensive reactions w/ MAOIs including agents w/ similar properties eg, furazolidone & procarbazine. Elevated risk of arrhythmias w/ anaesth w/ halogenated hydrocarbons. Potential additive bronchodilating effect w/ other β-adrenergic or anticholinergic drugs. Hypokalaemia may increase disposition towards arrhythmias in patients treated w/ digitalis glycosides.