<p>Beta-blockers (including eye drops) should be avoided in asthmatic patients. If beta-blockers are administered for compelling reasons, the effect of formoterol will be reduced or abolished. On the other hand, concomitant use of other beta adrenergic drugs can have potentially additive effects, therefore caution is required when theophylline or other beta adrenergic drugs are prescribed concomitantly with formoterol. Concomitant treatment with quinidine, disopyramide, procainamide, phenothiazines, antihistamines, monoamine oxidase inhibitors and tricyclic antidepressants can prolong the QTc-interval and increase the risk of ventricular arrhythmias.</p>