A 55-year-old man with schizophrenia on long-term haloperidol develops persistent orofacial choreiform movements. His physician considers switching to a vesicular monoamine transporter inhibitor. The drug and its mechanism are:
- A Amantadine, enhancing striatal dopamine release
- B Pramipexole, stimulating D2/D3 receptors presynaptically
- C Tetrabenazine, depleting presynaptic dopamine stores by blocking VMAT2 ✓
- D Entacapone, inhibiting peripheral COMT-mediated degradation
Correct answer: C. Tetrabenazine, depleting presynaptic dopamine stores by blocking VMAT2
Explanation
Tardive dyskinesia reflects dopaminergic supersensitivity in the nigrostriatal pathway after chronic D2 blockade. Tetrabenazine inhibits VMAT2, the vesicular monoamine transporter, depleting stored dopamine from presynaptic terminals and thereby damping the excess dopaminergic drive, and it is an established treatment for tardive dyskinesia. Amantadine and pramipexole increase dopaminergic tone and would worsen the movements, while entacapone is a peripheral levodopa adjunct with no role here.
Reference: Goodman and Gilman The Pharmacological Basis of Therapeutics, 14th ed.
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