A 24-year-old man started on an SSRI presents with agitation, clonus, hyperreflexia, diarrhoea and a temperature of 39 degrees Celsius after he self-medicated with an over-the-counter cough preparation containing dextromethorphan. Which antidote is the specific antagonist used in severe serotonin syndrome?
- A Cyproheptadine ✓
- B Flumazenil
- C Naloxone
- D Physostigmine
Correct answer: A. Cyproheptadine
Explanation
Serotonin syndrome results from excessive serotonergic activity at central 5-HT1C and 5-HT2C receptors. Cyproheptadine is a first-generation antihistamine with potent 5-HT2C antagonism and is the accepted specific antidote in moderate to severe cases, given orally or via nasogastric tube. Supportive care with benzodiazepines and cooling accompanies it. Physostigmine was historically used but carries cholinergic risk, flumazenil reverses benzodiazepines, and naloxone reverses opioids, none of which addresses serotonergic excess.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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