Partial agonist for 5-HT1A, D2 and D3 with high affinity for D2 and D3 describes which agent?

• A. Aripiprazole
• B. Brexpiprazole
• C. Quetiapine
• D. Ziprasidone

Answer: (B)

Partial agonism at dopamine receptors with activity at serotonin receptors is a key mechanism of many atypical antipsychotics. Brexpiprazole fits this pattern because it binds with high affinity to D2 and D3 receptors and acts as a partial agonist at both, while also serving as a partial agonist at 5-HT1A receptors. This combination provides antipsychotic effects by modulating dopaminergic signaling without producing the full blockade that leads to more EPS, and the 5-HT1A partial agonism contributes to mood and anxiety symptom effects. The drug’s profile also includes 5-HT2A antagonism, which helps with other symptoms and side-effect differences compared with plain D2 antagonists.

Aripiprazole is another D2/D3 partial agonist with 5-HT1A partial agonism, but brexpiprazole’s higher D3 affinity and its distinct balance of receptor activities make it the option described in the question. Quetiapine and ziprasidone are not partial agonists at D2 (they act more as antagonists at D2), so they don’t match the description.