title: Co-administration of sub-antinociceptive doses of oxycodone and morphine produces marked antinociceptive synergy with reduced CNS side-effects in rats.
abstract: Oxycodone and morphine are structurally related, strong opioid analgesics, commonly used to treat moderate to severe pain in humans. Although it is well-established that morphine is a mu-opioid agonist, this is not the case for oxycodone. Instead, our recent studies have shown that oxycodone appears to be a kappa-opioid agonist (Ross and Smith, 1997). In the current study, we now show that co-administration of sub-antinociceptive doses of oxycodone (putative kappa-opioid agonist) with morphine (mu-opioid agonist) to rats by both the intracerebroventricular and by systemic routes (intraperitoneal and subcutaneous), results in markedly increased (synergistic) levels of antinociception. Behaviourally, rats co-administered sub-antinociceptive doses of oxycodone and morphine were similar to control rats dosed with saline, whereas rats that received equi-potent doses of either opioid alone, were markedly sedated. These results suggest that co-administration of sub-analgesic doses of oxycodone and morphine to patients may provide excellent pain relief with a reduction in opioid-related CNS side-effects. Controlled clinical trials in appropriate patient populations are required to evaluate this possibility.(1)
authors.affiliation: School of Pharmacy, The University of Queensland, St Lucia, Brisbane, Australia.
authors.forename: F B
authors.initials: FB
authors.lastname: Ross
authors.forename: S C
authors.initials: SC
authors.lastname: Wallis
authors.forename: M T
authors.initials: MT
authors.lastname: Smith
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002490:Central Nervous System / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004357:Drug Synergism; D007274:Injections, Intraperitoneal; D007276:Injections, Intraventricular; D007279:Injections, Subcutaneous; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects*; D010098:Oxycodone / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000701:Analgesics, Opioid; D004338:Drug Combinations; D009020:Morphine; D010098:Oxycodone