Aripiprazole differs from most other second-generation antipsychotics because its primary action at the dopamine D2 receptor is:
- A Irreversible antagonism
- B Inverse agonism
- C Partial agonism ✓
- D Competitive antagonism with allosteric potentiation by serotonin blockade
Correct answer: C. Partial agonism
Explanation
Aripiprazole is a partial agonist at D2 receptors, acting as a functional antagonist in hyperdopaminergic mesolimbic states and as a functional agonist in hypodopaminergic nigrostriatal regions, which explains its low propensity for extrapyramidal symptoms and hyperprolactinemia. It is also a partial agonist at 5-HT1A and an antagonist at 5-HT2A. Irreversible antagonism is not a property of any antipsychotic, and simple competitive D2 blockade characterises drugs like risperidone.
Reference: Stahl's Essential Psychopharmacology, 4th ed.
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