A patient on fluoxetine inadvertently receives pethidine and develops agitation, hyperthermia, clonus and diarrhoea consistent with serotonin syndrome. Alongside supportive care and benzodiazepines, the specific antidote used for severe cases is:
- A Cyproheptadine ✓
- B Naloxone
- C Physostigmine
- D Flumazenil
Correct answer: A. Cyproheptadine
Explanation
Serotonin syndrome results from excessive serotonergic activity, particularly at 5-HT2B and 5-HT1B receptors. Cyproheptadine, a first-generation antihistamine with potent 5-HT2B antagonist properties, is the accepted antidote in moderate to severe cases and is given orally or via nasogastric tube. Naloxone reverses opioids, physostigmine treats anticholinergic syndromes, and flumazenil reverses benzodiazepine overdose, none of which addresses serotonergic excess. Chlorpromazine is an injectable alternative where available.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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