Which antipsychotic is among those considered less likely to worsen Parkinson disease symptoms, and is listed as an exception in Beers criteria?

• A. Clozapine
• B. Haloperidol
• C. Quetiapine
• D. Olanzapine

Answer: (C)

The key idea is that drugs which block dopamine in the nigrostriatal pathway tend to worsen Parkinson disease motor symptoms, so antipsychotics differ in how much they disrupt that pathway. Haloperidol is a potent D2 blocker with a high risk of extrapyramidal symptoms, making it more likely to aggravate PD. Quetiapine, on the other hand, has relatively weak and transient D2 receptor blockade and a broader receptor profile, so it produces far fewer extrapyramidal effects. This lower risk of worsening motor symptoms is why quetiapine is favored in Parkinson disease-related psychosis and is noted as an exception in Beers Criteria guidelines for older adults.

Clozapine also has low EPS risk, but it carries a significant risk of agranulocytosis and requires regular blood monitoring, which limits its designation as a general exception. Olanzapine can be safer for EPS than haloperidol but has other drawbacks like metabolic effects, so those factors are why it’s not the standout exception here.