This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'A patient on cisplatin therapy develops intractable vomiting on the third day of treatment. The agent of choice for controlling this vomiting is : \nSelect and explain. \nA. Aprepitant, B. Ondansetron, C. Metoclopramide, D. Prochlorperazine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Cisplatin-induced vomiting has two phases.\n\nEarlyPhase: It occurs within the first 24 hours. 5 HT3 antagonists like ondansetron are the agents of choice for this condition.\nDelayed Phase: Vomiting occurring after 24 hours is less responsive to ondansetron and other drugs. It is best controlled by substance P antagonist like aprepitant.', 'role': 'assistant'}]