Increased effects w/ ritonavir, cobicistat. Reduced formoterol effect w/ β-blockers. Increased formoterol effect w/ other β-adrenergic drugs. ECG changes & increased risk of ventricular arrhythmias w/ quinidine, disopyramide, procainamide, antihistamines, MAOIs, TCAs, phenothiazines. Lowered cardiac tolerance to β
2 agonist w/ L-dopa, L-thyroxine, oxytocin, alcohol. Increased BP w/ MAOIs, furazolidone, procarbazine. Increased risk of hypokalaemia w/ digoxin, theophylline, aminophylline, steroids, diuretics. Increased risk of abnormal heart rhythms w/ some anaesth.