<p>Concomitant treatment with xanthine derivatives, steroids or diuretics may potentiate a possible hypokalaemic effect of beta-agonists. Increased susceptibility to cardiac arrhythmias in patients treated with digitalis. Concomitant use with quinidine, disopyramide, procainamide, phenothiazines, antihistamines, MAOI or TCAs can prolong the QT-interval and increase the risk of ventricular arrhythmias. L-dopa, L-thyroxine, oxytocin and alcohol can impair cardiac tolerance towards beta2-sympathomimetics. beta-adrenergic blockers can inhibit the effect of formoterol. Increased risk of arrhythmias in patients receiving concomitant anaesthesia with halogenated hydrocarbons.</p>