Clozapine's superior efficacy in treatment-resistant schizophrenia compared to typical antipsychotics is partly attributed to its unique receptor pharmacology. Which of the following BEST describes the key differentiating feature?
- A Highest D2 occupancy (>90%) among all antipsychotics, saturating striatal dopamine receptors
- B Selective D3 receptor antagonism in the mesolimbic pathway without D2 binding
- C High D4 receptor affinity combined with 5-HT2A antagonism, D1 partial agonism, and 'fast-off' kinetics at D2 receptors ✓
- D Irreversible covalent blockade of D2 receptors, providing long-lasting antipsychotic effect
Explanation
Clozapine achieves only 40–60% D2 occupancy (well below the >80% occupancy of typical antipsychotics) but dissociates very rapidly from D2 receptors ('fast-off' or 'hit-and-run' kinetics), allowing physiological dopamine pulses to break through — reducing EPS and hyperprolactinaemia. It also has potent 5-HT2A antagonism (reducing negative symptoms), high D4 and D1 affinity, and potent alpha-1, muscarinic, and histaminergic blockade. The 'fast-off' kinetics and multi-receptor pharmacology together explain its unique efficacy and side-effect profile. Clozapine does not bind covalently or selectively to D3.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.