Potential Cytochrome P450 Drug-Drug Interaction Among Adult and Adolescent Patients Undergoing Tonsillectomy

OBJECTIVE: To assess the frequency of potential drug-drug interactions affecting cytochrome P450 (CYP)–mediated metabolism of opioids among adult and adolescent patients who underwent adenotonsillectomy. STUDY DESIGN: Retrospective chart review. SETTING: Tertiary care university hospital. PATIENTS AND METHODS: A retrospective review was conducted of 279 patients who underwent adenotonsillectomy at the University of Rochester. The discharge medication list was reviewed for all patients, and their postoperative medications were compared with a reference list published by the Food and Drug Administration and the University of Indiana’s Department of Clinical Pharmacology (Flockhart Table) to determine whether CYP-inducing or CYP-inhibiting medication was present. RESULTS: Out of 279 patients, 197 different medications were taken postoperatively. Approximately 70% of patients were taking 2 medications in addition to the standard postoperative analgesics (acetaminophen, hydrocodone, oxycodone, morphine, and/or ibuprofen). The 5 most commonly prescribed medications excluding the posttonsillectomy medications were oral contraceptives, ondansetron, amoxicillin, albuterol, and methylprednisolone. Four percent of patients were taking a medication that inhibits CYP3A4; <1% were taking a medication that induces CYP3A4; and 15% were taking a medication that inhibits CYP2D6. CONCLUSIONS: Nearly 20% of the patients in this cohort were taking a medication that may alter opioid metabolism through induction or inhibition of CYP3A4 or CYP2D6. Some of these interactions have the potential to be more clinically relevant than others, particularly interactions that can lead to enhanced toxicity of opioids due to accumulation of active metabolites.