A patient on fluoxetine develops agitation, hyperthermia, clonus and diarrhoea. Which drug, useful in serotonin syndrome, acts by blocking both 5-HT1A and 5-HT2 receptors along with H1 receptors?

• A Ondansetron
• B Chlorpromazine
• C Propranolol
• D Cyproheptadine ✓

Explanation

Cyproheptadine is a first-generation antihistamine with potent 5-HT2 antagonism and additional 5-HT1A blockade, making it the classical antidote used in serotonin syndrome alongside supportive care. Ondansetron blocks only 5-HT3 receptors, propranolol provides beta-blockade without meaningful serotonergic antagonism, and chlorpromazine has dopamine B2 antagonism with some 5-HT2 affinity but is not the conventional agent cited for this indication.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

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