This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Pharmacology
Pure opioid antagonist: 
Select and explain. 
A. Naloxone, B. Buprenorphine, C. Pentazocine, D. Morphine
A: Naloxone
Answer: A: Naloxone 
Explanation: Ans. A. NaloxoneNaloxone, naltrexone and nalmefene are potent mu receptor antagonist with significant blocking action on kappa and delta. Naloxone is short acting and naltrexone is long acting. Naloxone is drug of choice for acute opioid poisoning. Naltrexone is used for maintenance therapy for opioid poisoning.