Serotonin syndrome due to concomitant use of linezolid and methadone.

Serotonin syndrome is a potentially life-threatening adverse drug reaction typically caused by a single or combination of two or more medications with serotonergic properties due to increased serotonin release. Our case is a 60-year-old drug-addict man who was admitted to the poisoning department of Loghman hospital with methadone poisoning. On the fifth day of hospitalization and after initiating the linezolid treatment for VAP, the patient began to run a fever with agitation, tremor, spontaneous clonus movement in the hands, and tachycardia. Due to patients' manifestations and after ruling out other diagnoses, serotonin syndrome was confirmed with the possibility of concomitant use of linezolid and methadone. Linezolid administration was promptly discontinued, and vancomycin therapy was initiated (1000 mg twice a day intravenously). Supportive therapies were performed. Finally, tremor, rigidity, and clonus movement disappeared within 48 h.