## Tardive Dyskinesia and Antipsychotic Selection **Key Point:** Tardive dyskinesia (TD) is an involuntary movement disorder caused by prolonged exposure to typical (first-generation) antipsychotics. Once established, it may persist even after drug discontinuation. ### Risk Profile by Antipsychotic Class | Antipsychotic Class | TD Risk | Mechanism | Clinical Implication | | --- | --- | --- | --- | | **Typical (1st gen)** | Very High (20–30% over 5 years) | D~2~ receptor blockade → denervation supersensitivity | Avoid in established TD | | **Atypical (2nd gen)** | Low (1–5% over 5 years) | Rapid D~2~ dissociation + serotonin antagonism | Preferred in TD | | **Quetiapine** | Lowest (<1%) | Weak D~2~ binding, rapid dissociation | Best choice for TD | **High-Yield:** Quetiapine has the lowest risk of tardive dyskinesia among all antipsychotics due to its rapid dissociation from dopamine receptors and minimal striatal D~2~ occupancy. ### Why Quetiapine is Optimal Here 1. **Atypical mechanism:** Rapid D~2~ dissociation reduces risk of movement disorders. 2. **Lowest TD risk:** Even lower than other atypicals (risperidone, olanzapine). 3. **Efficacy maintained:** Still effective for psychotic symptoms despite lower D~2~ affinity. 4. **May improve existing TD:** Some evidence suggests atypicals can stabilize or improve established TD. **Clinical Pearl:** When a patient develops tardive dyskinesia on a typical antipsychotic, switching to an atypical (especially quetiapine) is the standard of care. Continuing or increasing the offending agent worsens TD. **Warning:** Do NOT continue haloperidol or switch to another typical antipsychotic (chlorpromazine, fluphenazine) — this will perpetuate or worsen the dyskinesia.
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