A patient presented with right lower quadrant pain. He was already treated for right renal stone disease. Which of the following opioid is partial agonist at MU and full agonist at Kappa?

ANS. APentazocine: Partial agonist and antagonist at mu receptor, and agonist at kappaBuprenorphine: Partial agonist at mu and antagonist at kappaTramadol: Affinity for mu is low, while that for kappa and delta is very low. (Tramadol also has an additional mechanism of inhibiting reuptake of NA and 5-HT, and thus activating monoaminergic spinal inhibition of pain. Its analgesic action is only partially reversed by opioid antagonist naloxone.Fentanyl: Congener of pethidine, 80-100 times more potent than morphine. It is chemically unrelated to morphine, but interacts with opioid receptors and its actions are blocked by naloxone.