A young man on fluoxetine presents with agitation, clonus, hyperreflexia, diarrhoea and low-grade fever after taking an additional serotonergic agent. Alongside supportive care and benzodiazepines, the specific antidote used for moderate to severe serotonin syndrome is:
- A Propranolol
- B Ondansetron
- C Cyproheptadine ✓
- D Haloperidol
Correct answer: C. Cyproheptadine
Explanation
Cyproheptadine is a first-generation antihistamine with potent 5-HT2A antagonist activity, and blockade of 5-HT2A receptors is central to reversing the neuromuscular findings of serotonin syndrome. Ondansetron is a 5-HT3 antagonist and does not address the 5-HT2A mediated clonus and hyperreflexia. Propranolol may mask tachycardia without treating the serotonergic excess, and haloperidol lowers seizure threshold. Cyproheptadine is given orally or via nasogastric tube in divided doses.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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