Drug Interactions between darunavir and fluticasone / salmeterol

GENERALLY AVOID: Coadministration with potent inhibitors of CYP450 3A4 may significantly increase the systemic levels and pharmacologic effects of salmeterol, which is primarily metabolized by the isoenzyme. Because salmeterol prolongs the QT interval in a dose-dependent manner, high systemic levels of salmeterol may increase the risk of ventricular arrhythmias such as ventricular tachycardia, ventricular fibrillation, and torsade de pointes. In a placebo-controlled, crossover drug interaction study consisting of 20 healthy subjects, coadministration of salmeterol (50 mcg twice daily) and the potent CYP450 3A4 inhibitor ketoconazole (400 mg once daily) for 7 days resulted in a 16-fold increase in plasma salmeterol exposure (AUC) mainly due to increased bioavailability of the swallowed portion of the dose. Peak plasma salmeterol concentrations (Cmax) were increased by 1.4-fold, and three out of 20 subjects (15%) were withdrawn from the combination due to salmeterol-mediated systemic effects (two with QTc prolongation and one with palpitations and sinus tachycardia). Coadministration of salmeterol and ketoconazole did not result in a clinically significant effect on mean heart rate, blood potassium, or blood glucose. Although there was no statistical effect on the mean QTc, the combination was associated with more frequent increases in QTc duration than salmeterol and placebo.

MANAGEMENT: Concomitant use of salmeterol with potent CYP450 3A4 inhibitors is not recommended. Some authorities recommend avoiding concomitant use of salmeterol during and for 2 weeks after treatment with itraconazole. Other authorities consider concomitant use of salmeterol and atazanavir-cobicistat to be contraindicated.

MONITOR: Coadministration with moderate inhibitors of CYP450 3A4 may increase the systemic exposure to fluticasone following intranasal administration or oral inhalation. Fluticasone undergoes extensive first-pass and systemic metabolism via CYP450 3A4, thus inhibition of the isoenzyme may significantly increase systemic bioavailability of the drug. However, the extent of interaction may depend on the route of fluticasone administration and the specific formulation. Multiple case reports describe instances of adrenal insufficiency and Cushing's syndrome associated with concomitant use of inhaled fluticasone and the azole antifungal fluconazole, a moderate CYP450 3A4 inhibitor.

MANAGEMENT: Monitor for signs and symptoms of hypercorticism if intranasal or orally inhaled fluticasone is coadministered with a moderate inhibitor of CYP450 3A4. Signs and symptoms of hypercorticism include acne, striae, thinning of the skin, easy bruising, moon facies, dorsocervical "buffalo" hump, truncal obesity, increased appetite, acute weight gain, edema, hypertension, hirsutism, hyperhidrosis, proximal muscle wasting and weakness, glucose intolerance, exacerbation of preexisting diabetes, depression, and menstrual disorders. Other systemic glucocorticoid effects may include adrenal suppression, immunosuppression, posterior subcapsular cataracts, glaucoma, bone loss, and growth retardation in children and adolescents. Signs and symptoms of adrenal insufficiency include anorexia, hypoglycemia, nausea, vomiting, weight loss, muscle wasting, fatigue, weakness, dizziness, postural hypotension, depression, and adrenal crisis manifested as inability to respond to stress (e.g., illness, infection, surgery, trauma). Systemic glucocorticoids may be necessary until adrenal function recovers.

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.