A slow-release opioids drug system for postoperative pain relief

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It would be very convenient and practical that a slow release of opioid injected into the epidural space is able to be effective for 3〜4 days in postoperative patients. A copolymer paste containing opioid is such one possibility to provide more effective and convenient mean for postoperative analgesia.To examine such possibility as well as safety of epidural administration of an old opioid, oxycodone which, with oral slow releasing tablet, has recently been used in the US, we have done rats' experiments and found that oxycodone administered into the pontine reticular formation did not cause any sedative and analgesic effect, but its spinal administration caused a potent analgesia. Charbacol, a muscarinic agonist, produced analgesic action when administered both into the pontine and into the spinal subarachnoid space. Since morphine affects phosphorylation of MAPK kinase, we examined such effects of oxycodone using PC12 cell line and found that oxycodone did not affect activation of MAPK kinase. Then we have done clinical studies to examine effect of epidural oxycodone in 60 postoperative patients after approving with the human investigation committee. We found that epidural oxycodone is similarly effective for postoperative pain with less side effects such as nausea and vomiting.Although we could not be able to make a slow releasing solution of opioid which is available for epidural administration, it would provide a prolong analgesia for 3-4 days even with a single injection of such slow release of opioid into the epidural space. Since a drug company has recently started to make such injectable opioid with slow releasing property, research for a new drug-delivery system for injectable opioid would be promising.