This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal tract, Subject name: Pharmacology
For chemotherapy induced vomiting, 5HT3 antagonist having maximum potency is: 
Select and explain. 
A. Ondansetron, B. Granisetron, C. Dolasetron, D. Palonosetron
D: Palonosetron
Answer: D: Palonosetron 
Explanation: it is the longest acting and highest affinity towards 5HT3 receptor used in chemotherapy induced vomiting ESSENTIAL OF MEDICAL PHARMACOLOGY SEVENTH EDITION KD TRIPATHI PG NO .669