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
Opioid agonist-antagonist is - 
Select and explain. 
A. Pethidine, B. Pantazocine, C. Buprenorphine, D. Methadone
B: Pantazocine
Answer: B: Pantazocine 
Explanation: Ans. is 'b' i.e., Pantazocine Agonist-antagonists (k analgesics) - Nalorphine, Pentazocine, Butorphenol. Paial/weak agonist + x antagonist - Buprenorphine. Pure antagonists - Naloxone, Naltrexone, Nalmefene. o Clinically agonist - Antagonists and paial/weak agonists are analgesics of comparable efficacy to low doses of morphine and they cause low ceiling respiratory depression, and have lower abuse potential. Impoant points about specific agents. Butorphanol (paial agonist & weak antagonsit, x agonist) o Analgesia and respiratory depression have a lower ceiling. o It causes equivalent analgesia but more sedation than morphine. The most outstanding feature is that butorphanol can neither substiture for nor antagonize morphine --> weak interaction with receptors.