Major
Budesonide × ritonavir
Inhaled corticosteroids (ICS)×HIV protease inhibitor / pharmacokinetic booster
Mechanism
Ritonavir is the most potent CYP3A4 inhibitor available. Systemic budesonide exposure (inhaled or oral) rises 8- to 10-fold. High risk of iatrogenic Cushing's syndrome, especially during long-term inhaled therapy for asthma or COPD.
Symptoms
Moon face, central obesity, abdominal striae, hypertension, hyperglycaemia. With prolonged combination and abrupt withdrawal: adrenal insufficiency risk.
Management
Avoid the combination. Alternative inhaled corticosteroid: beclomethasone (less CYP3A4-dependent) or short-acting β2-agonists with inhaled anticholinergics. If replacement is impossible: minimum effective budesonide dose with glucose and blood pressure monitoring.