Question

_______ antiemetic selectively blocks levodopa induced vomiting without blocking its antiparkinsonian action.

• A. \( \text{Metoclopramide} \)
• B. \( \text{Cisapride} \)
• C. \( \text{Domperidone} \)
• D. \( \text{Ondansetron} \)

Hint:

Remember Domperidone as the antiemetic that's "brain-shy" – it stays mostly in the periphery, blocking vomiting without messing with Parkinson's meds in the brain.

Answer 1

The Correct Option is C

Levodopa, used in the treatment of Parkinson's disease, can cause nausea and vomiting by stimulating dopamine D$_2$ receptors in the chemoreceptor trigger zone (CTZ) of the brainstem. Domperidone is a peripheral dopamine D$_2$ receptor antagonist that does not readily cross the blood-brain barrier. This selective action allows it to block the emetic effects of levodopa by acting on the CTZ, which lies outside the blood-brain barrier, without significantly interfering with the central dopaminergic effects of levodopa that are crucial for its antiparkinsonian action. Metoclopramide also blocks D$_2$ receptors but can cross the blood-brain barrier and may antagonize the antiparkinsonian effects of levodopa. Cisapride is primarily a prokinetic agent affecting serotonin receptors in the gut. Ondansetron is a 5-HT$_3$ receptor antagonist, mainly used for chemotherapy-induced nausea and vomiting.