Introduction Antiretroviral medications have the potential to produce serious drug interactions by interfering with the hepatic cytochrome P450 cascade. Ritonavir, a protease inhibitor, is a known CYP450 inhibitor that is commonly used in the treatment of HIV¹. Iatrogenic Cushing’s syndrome is caused by exposure to glucocorticoids and may be promoted by interaction with additional drugs that result in hypothalamic-pituitary adrenal axis suppression². It is well documented in HIV patients receiving inhaled steroids in combination with a ritonavir-containing antiretroviral regimen³. Following one such severe drug-drug interaction in a patient, a clinical audit was conducted to identify potential drug-drug interactions in a HIV clinic at Beaumont Hospital, Dublin.

Methods 200 patients receiving Ritonavir were interviewed and screened for harmful prescribed and non-prescribed co-medications. Patients receiving regular steroid doses and Ritonavir were identified and all drugs were cross-referenced to the Liverpool Drug Interactions website to highlight any dangerous drug interactions.

Results 86% of patients had concomitant prescribed medications, three-quarters of which were undocumented. Furthermore, 45% of patients used regular over the counter-medication and 2.7% used recreational drugs. 8% of patients were flagged for potentially dangerous drug-drug interactions and of these, 15% contained steroids.

Discussion The interaction between corticosteroids and PIs is significant and deserves close attention and evaluation. Timely communication among all prescribing physicians for a given patient is indicated in order to proactively detect significant interactions before they manifest themselves clinically.