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 cancer patient who is on cisplatin therapy develops severe vomiting on the 1st day of treatment,  drug indicated to treat this is: \nSelect and explain. \nA. Aprepitant., B. Ondansetron, C. Fosaprepitant., D. All of the above.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Cisplatin induced vomiting has two phases.\n\nEarlyPhase: It occurs within 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'}]