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
A patient on cisplatin therapy develops intractable vomiting on the third day of treatment. The agent of choice for controlling this vomiting is : 
Select and explain. 
A. Aprepitant, B. Ondansetron, C. Metoclopramide, D. Prochlorperazine
A: Aprepitant
Answer: A: Aprepitant 
Explanation: Cisplatin-induced vomiting has two phases.

EarlyPhase: It occurs within the first 24 hours. 5 HT3 antagonists like ondansetron are the agents of choice for this condition.
Delayed Phase: Vomiting occurring after 24 hours is less responsive to ondansetron and other drugs. It is best controlled by substance P antagonist like aprepitant.