Which antiemetic blocks dopamine stimulation in the chemoreceptor trigger zone?

Which antiemetic blocks dopamine stimulation in the chemoreceptor trigger zone?

• A. Ondansetron
• B. Promethazine
• C. Dimenhydrinate
• D. Metoclopramide

Answer: (D)

Blocking dopamine signaling in the chemoreceptor trigger zone reduces the vomiting reflex triggered by toxins or chemotherapy. Metoclopramide does exactly that: it acts as a dopamine D2 receptor antagonist in the CTZ, preventing the emetic signals from reaching the vomiting center. It also has prokinetic effects through 5-HT4 receptor agonism, which can help with nausea related to slowed gastric emptying. The other common antiemetics work through different pathways: ondansetron blocks 5-HT3 receptors, while promethazine and dimenhydrinate are H1 antihistamines with anticholinergic effects that mainly address vestibular or gut-related symptoms rather than CTZ dopamine blockade.

Blocking dopamine signaling in the chemoreceptor trigger zone reduces the vomiting reflex triggered by toxins or chemotherapy. Metoclopramide does exactly that: it acts as a dopamine D2 receptor antagonist in the CTZ, preventing the emetic signals from reaching the vomiting center. It also has prokinetic effects through 5-HT4 receptor agonism, which can help with nausea related to slowed gastric emptying. The other common antiemetics work through different pathways: ondansetron blocks 5-HT3 receptors, while promethazine and dimenhydrinate are H1 antihistamines with anticholinergic effects that mainly address vestibular or gut-related symptoms rather than CTZ dopamine blockade.