Fatal Carbamazepine Overdose in a Polysubstance User: Polydrug Use Alters the Clinical Presentation – Case Report

Carbamazepine (CBZ) overdose is a known cause of neurotoxicity and cardiotoxicity. However, its clinical presentation may be masked in poly-drug users, leading to diagnostic and therapeutic challenges. We report a case of a 40-year-old man with a history of psychosis and substance addiction who was admitted to the Medical Emergency Department of the University Hospital Center Saadna Abdennour in Setif, Algeria, following an intentional ingestion of 60 g of CBZ approximately 20 hours prior to admission. On arrival, the patient exhibited a Glasgow Coma Scale (GCS) score of 10/15 without convulsions and stable vital signs. Laboratory tests revealed hyperkalemia (6.07 mmol/L), and toxicological screening detected cannabis, benzodiazepines, MDMA, and opioids. The plasma CBZ concentration was critically elevated at 50.8 mg/L. Despite initial supportive care, the patient experienced a fatal cardiorespiratory arrest 40 hours post-ingestion. This case underscores the clinical pitfalls in assessing CBZ intoxication in poly-drug users. The concomitant use of benzodiazepines and opioids likely masked the convulsive presentation of CBZ toxicity, misleading physicians into underestimating its severity. Furthermore, the absence of early electrocardiographic monitoring contributed to the delayed recognition of CBZ-related cardiotoxicity. The depressive effects of CBZ, opioids, and benzodiazepines on the central nervous system and respiratory drive played a critical role in the fatal outcome. This report highlights the importance of considering polysubstance interactions in acute toxicology cases and emphasizes the necessity of systematic ECG evaluation and vigilant monitoring in CBZ overdose, particularly in patients with concurrent psychoactive substance use.