Functional Pharmacobezoar and Bowel Ischemia Requiring Hemicolectomy Complicating Extended-Release Carbamazepine-Venlafaxine Overdose

BACKGROUND: Overdoses of extended-release (ER) medications can cause life-threatening toxicity from prolonged gastrointestinal drug retention due to pharmacobezoar formation. This may result in severe complications including delayed serotonin syndrome and intestinal ischemia despite early use of enhanced elimination strategies. CASE SUMMARY: A 45-year-old woman presented with altered mental status following carbamazepine-venlafaxine ER overdose. Initial carbamazepine concentration was 163 μmol/L. She suffered a ventricular tachycardia arrest requiring venoarterial extracorporeal membrane oxygenation and enhanced elimination with continuous renal replacement therapy (CRRT). After CRRT, carbamazepine concentration rebounded from 33 to 80 μmol/L and clinical features of serotonin syndrome developed suggesting ongoing absorption. CT revealed cecal pneumatosis with obstruction. Laparotomy at day 9 revealed transmural ischemic necrosis with 4-6 L of retained charcoal and polyethylene glycol mixture; source control required a right hemicolectomy. Carbamazepine concentration declined postoperatively and serotonergic symptoms resolved. CONCLUSIONS: Carbamazepine-venlafaxine ER overdose with retained pill fragments can cause a variety of complications including prolonged toxicity. Rebounding drug concentration following enhanced elimination should trigger an investigation for gastrointestinal sequestration and prompt surgical consultation.