Clozapine's superior efficacy in treatment-resistant schizophrenia compared with typical antipsychotics is primarily attributed to its:
- A Very high D2 receptor occupancy (>90%) in the striatum
- B Selective blockade of D4 receptors in the prefrontal cortex only
- C Lower D2 occupancy combined with high serotonin 5-HT2A, muscarinic, and histamine H1 receptor antagonism ✓
- D Agonism at D3 receptors in the limbic system
Correct answer: C. Lower D2 occupancy combined with high serotonin 5-HT2A, muscarinic, and histamine H1 receptor antagonism
Explanation
Clozapine has relatively low D2 receptor occupancy (~60–65% at therapeutic doses) but is a potent antagonist at serotonin 5-HT2A, 5-HT2C, muscarinic (M1–M4), histamine H1, and alpha-adrenergic receptors. The combination of partial D2 blockade and multi-receptor antagonism — especially the 5-HT2A/D2 ratio — is thought to explain its superior efficacy for positive, negative, and cognitive symptoms, and its lower propensity for extrapyramidal side effects compared with high-D2-occupancy typical antipsychotics.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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