Drug Interactions between fluticasone / salmeterol and methazolamide

MONITOR: Coadministration with beta-2 adrenergic agonists may potentiate the hypokalemic effects of potassium-wasting diuretics. Beta-2 agonists can cause clinically significant but usually transient decreases in serum potassium concentrations. Since QT prolongation is a possible side effect of beta-2 agonists, exacerbation of hypokalemia may increase the risk of torsade de pointes and other serious arrhythmias. The interaction may be more likely with systemic or nebulized formulations of beta-2 agonists, high dosages of inhaled beta-2 agonists, or concomitant theophylline or corticosteroid therapy.

MANAGEMENT: Caution is advised when beta-2 agonists are used with potassium-wasting diuretics. Serum potassium level and cardiovascular status should be monitored, especially if the beta-2 agonist is administered systemically or by nebulizer. Patients should be advised to notify their physician if they experience potential signs and symptoms of hypokalemia such as fatigue, weakness, myalgia, muscle cramps, numbness, tingling, abdominal pain, constipation, palpitation, and irregular heartbeat.

Although they are often combined in clinical practice, the concomitant use of beta-2 adrenergic agonists and corticosteroids may result in additive hypokalemic effects. Since beta-2 agonists can sometimes cause QT interval prolongation, the development of hypokalemia may potentiate the risk of ventricular arrhythmias including torsade de pointes. However, clinical data are limited, and the potential significance is unknown. Patients who are receiving systemic or nebulized formulations of beta-2 agonists, high dosages of inhaled beta-2 agonists, or systemic corticosteroid therapy may be at a greater risk of developing hypokalemia.