Which antiemetic medication blocks the 5-HT3 serotonin receptor and may cause extrapyramidal symptoms?

Metoclopramide is the antiemetic medication that predominantly blocks the 5-HT3 serotonin receptor while also affecting dopamine receptors, particularly D2 receptors. This dual mechanism can lead to various side effects, one of which includes extrapyramidal symptoms (EPS). These symptoms are a result of dopamine receptor antagonism and can manifest as movement disorders, including tremors, rigidity, and bradykinesia.

Ondansetron and granisetron are both selective 5-HT3 receptor antagonists and are primarily indicated for the prevention of nausea and vomiting, particularly related to chemotherapy or surgery, without causing significant extrapyramidal side effects. Prochlorperazine, while effective for nausea, operates primarily as a dopamine antagonist and is more likely to lead to EPS, but it does not primarily act on 5-HT3 receptors like metoclopramide does.

Thus, metoclopramide stands out as the correct choice because it combines the serotonin receptor blockade with the potential for dopamine-related movement disorders, leading to the risk of extrapyramidal symptoms.