This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous system, Subject name: Pharmacology
The most potent analgesic agent is: 
Select and explain. 
A. Fentanyl, B. Sufentanil, C. Remifentanil, D. Allentanil
B: Sufentanil
Answer: B: Sufentanil 
Explanation: Sulfentanil is 5 times more potent than Fentanyl.Alfentanil and remifentanil are faster acting and recovery is rapid. Above three drugs are congeners of Fentanyl. Ref: KD Tripathi 8th ed.