In patients with Parkinson disease, which antiemetic is considered inappropriate because it can worsen parkinsonian symptoms?

• A. Metoclopramide
• B. Clozapine
• C. Pimavanserin
• D. Quetiapine

Answer: (A)

The main idea is that in Parkinson disease, you want antiemetics that do not block dopamine receptors in the brain. Metoclopramide is a dopamine D2 receptor antagonist that crosses into the central nervous system, including the nigrostriatal pathway. Blocking dopamine there can worsen motor symptoms such as rigidity, slowness, and tremor, which is why metoclopramide is inappropriate for someone with Parkinson disease.

In contrast, the other options don’t act as typical antiemetics through strong D2 blockade. Pimavanserin targets 5-HT2A receptors and does not block dopamine receptors, so it won’t worsen parkinsonian motor symptoms. Quetiapine and clozapine are atypical antipsychotics with relatively lower risk of extrapyramidal symptoms and, while not antiemetics themselves, they do not carry the same risk of worsening motor symptoms from D2 antagonism.