Fentanyl-Induced Serotonin Syndrome 5 Days After Cessation of Serotonergic Agents: A Case Report

A 21-year-old patient with intellectual disability was admitted for gastroenteritis due to serotonergic medication overdose, and subsequently developed serotonin syndrome. Her symptoms initially improved after the cessation of serotonergic medications, but worsened 5 days later after fentanyl administration during general anesthesia. On emergence, she had convulsions and was nonresponsive. Subsequent imaging and electroencephalography did not demonstrate intracranial pathology or seizure activity. We suspect she had an exacerbation of her serotonin syndrome. She recovered successfully after supportive care. This case demonstrates that common medications used during anesthesia such as fentanyl can provoke serotonin syndrome, even several days after serotonergic drug discontinuation.