Effect of formoterol may be reduced w/ β-blockers. β-adrenergic drugs may increase the effects of formoterol. Quinidine, disopyramide, procainamide, antihistamines, phenelzine & isocarboxazid, amitryptiline & imipramine, phenothiazines can cause some changes in the ECG, heart trace & may also increase the risk of disturbances of heart rhythm. Levodopa, L-thyroxine, medicines containing oxytocin & alcohol can lower heart’s tolerance to formoterol. MAOIs, including drugs w/ similar properties eg, furazolidone & procarbazine can cause a rise in BP. Digoxin can cause a fall in blood K level. Theophylline, aminophylline or steroids & diuretics may cause a fall in K level. Some anaesth can increase the risk of abnormal heart rhythms.