Reduced Oxycodone Efficacy Associated With Carbamazepine Use in a Patient With Advanced Cholangiocarcinoma

Drug-drug interactions are a frequently under-recognised cause of suboptimal symptom control in palliative care.We describe a case of a 72-year-old woman with advanced cholangiocarcinoma who developed escalating abdominal pain despite increasing doses of oxycodone, including patient-controlled analgesia.Alternative explanations were considered, including disease progression, visceral pain, and psychological distress.Following opioid rotation to morphine, there was rapid improvement in analgesia, followed by features of opioid-induced neurotoxicity at moderate doses.A potentially clinically significant interaction between carbamazepine and oxycodone was subsequently identified.This case highlights the importance of recognising enzyme-inducing medications as a potential cause of reduced opioid efficacy and demonstrates the clinical value of opioid rotation in complex cases.