Clozapine is unique among antipsychotics in its efficacy in treatment-resistant schizophrenia. Beyond D2 blockade, which receptor binding profile best explains both its superior efficacy and its metabolic/cardiovascular side-effect profile?

• A High D1 and D4 antagonism with low H1 and M1 activity
• B Selective D3 blockade with moderate 5-HT1A partial agonism
• C Potent 5-HT2A, D4, M1, H1, and alpha-1 receptor antagonism with low D2 affinity ✓
• D Full D2 antagonism with sigma receptor agonism

Explanation

Clozapine is a multi-receptor 'dirty drug' with potent antagonism at 5-HT2A (contributing to fewer extrapyramidal effects and possibly superior efficacy), D4 (limbic system, possibly related to efficacy), M1 (producing constipation, dry mouth, urinary retention, cognitive effects), H1 (weight gain, sedation), and alpha-1 (orthostatic hypotension). Its relatively low D2 affinity explains minimal EPS. Weight gain and metabolic syndrome result partly from H1 and 5-HT2C antagonism. This polypharmacology distinguishes it from typical antipsychotics.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.