Clozapine's superior efficacy in treatment-resistant schizophrenia is partially attributed to its receptor binding profile. Which receptor combination best distinguishes clozapine from other second-generation antipsychotics?
- A High D2 affinity and moderate 5-HT2A blockade
- B Selective D3 receptor partial agonism
- C Low D2 affinity combined with high D4, 5-HT2A, alpha-1, H1, and muscarinic blockade ✓
- D Dopamine autoreceptor agonism causing presynaptic inhibition
Correct answer: C. Low D2 affinity combined with high D4, 5-HT2A, alpha-1, H1, and muscarinic blockade
Explanation
Clozapine has low affinity and loose (fast-off) binding to D2 receptors, which explains its low extrapyramidal side effect profile. Its therapeutic uniqueness comes from combined antagonism at D4, 5-HT2A (serotonin-dopamine balance), alpha-1 adrenoceptors (causing orthostasis), H1 histamine receptors (causing sedation and weight gain), and muscarinic receptors (causing constipation, sialorrhea paradoxically). This broad receptor profile — and particularly its glutamatergic modulation — may explain efficacy in treatment-resistant schizophrenia.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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