[Serotonin syndrome caused by an overdose of dextromethorphan, Medicon]

We report the first case of serotonin syndrome caused by overdose of dextromethorphan in Japan. A 34-year-old woman with schizophrenia received a dextromethorphan (Medicon) for a catarrhal symptom from two individual departments of the university hospital by chance. The daily amount of dextromethorphan was up to 180 mg for several days in addition to other regular antipsychotic drugs including risperidone, amitriptyline and levomepromazine. Finally, she was found in deep comatose state (GCS coma scale: E1V1M1) and the trachea was intubated in the emergency room. After admission to intensive care unit, the consciousness gradually improved; however, she was confused and agitated. The situation was normalized within next 24 hours and she was weaned from the mechanical ventilation next day. Serotonin syndrome demonstrates various signs and might be overlooked in an emergency room. Dextromethorphan is considered as a safe antitussive drug; however, the unexpected interaction should be suspected during chronic medical treatment.