Ritonavir is currently a commonly prescribed protease inhibitor for human immunodeficiency virus (HIV) infection. Its potent inhibition of hepatic cytochrome P450 3A4 isoenzyme may increase systemic glucocorticoids concentrations, leading to potential suppression of the hypothalamic pituitary adrenal axis (HPA) and iatrogenic Cushing's syndrome (CS).

We describe a case of a 43-year-old woman with HIV infection that presented with a clinical overt CS resulting from the interaction between ritonavir and intranasal budesonide at low doses. Similar cases have been described with long-term concomitant use of many glucocorticoids with ritonavir but very few concerning inhaled or intranasal budesonide.

This case reinforces the importance of physicians to be aware of this interaction, promoting its early recognition and providing a careful assessment of potentially serious drug–drug interactions, especially when ritonavir is prescribed to a HIV-patient with bronchial hyperresponsiveness or rhinitis.