◊ INTRODUCTION:
In this study, we investigated the dose requirements, pain relief, and side effects of oxycodone versus morphine after surgery with visceral pain.
◊ METHODS:
Ninety-one women received IV oxycodone or morphine before the end of laparoscopic hysterectomy and then continued with patient-controlled analgesia for 24 h postoperatively.
◊ RESULTS:
The accumulated oxycodone consumption was less (13.3 +/- 10.4 mg vs 22.0 +/- 13.1 mg, P = 0.001) than morphine. With oxycodone, the visual analog scale scores were significantly lower in the first hour postoperatively and sedation was less during the 24-h postoperative period, P = 0.006.
◊ CONCLUSIONS:
Oxycodone was more potent than morphine for visceral pain relief but not for sedation.
◊ Reviewed by S. Schug, MD, PhD
Chair of Anesthesiology,
Pharmacology and Anesthesiology Unit, Royal Perth Hospital, Perth, Australia
This is an interesting head-to-head comparison of the two opioids morphine and oxycodone through PCA in the setting of postoperative pain. The study revealed a higher potency and some other advantages of oxycodone, i.e. longer lasting effect of an initial bolus, better early analgesia (in the first postoperative hour), and less sedation over the 24 h study period.
Primarily based on studies with oral administration, oxycodone is commonly regarded as more potent than morphine. However, this may be due to the better oral bioavailability of oxycodone. For the parenteral route, a previous trial in breast and spinal surgery suggested equipotency of the two opioids [1], at least for somatic nociceptive pain. However, patients after hysterectomy suffer from a significant visceral pain component, on which oxycodone may act specifically. Such a specific effect on visceral pain would be in line with similar findings in another trial after abdominal surgery [2] and with experimental studies in visceral pain models in humans, for which superiority of oxycodone over morphine was shown after visceral stimulation [3,4].
There is debate on the reason for these differences. While in particular one research group argues in favor of a specific kappa receptor effect of oxycodone based on experiments in rodents [5], the clinical relevance of these findings in humans are challenged by others [6]. Irrespective of the pharmacological mechanism, the data presented here suggest benefits of using oxycodone over morphine with PCA pumps, at least in the setting of abdominal surgery.
This will require further investigation, but might be superseded by current studies which suggest important unexpected advantages by the combined use of oxycodone and morphine. A significant synergy and reduced adverse effects were initially described in rodent models [7] and then confirmed in clinical trials [8]. This has led to the development of a combination preparation by the pharmaceutical industry which aims at registration soon [9].
◊ References
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[2] Kalso E, Poyhia R, Onnela P, Linko K, Tigerstedt I, Tammisto T.
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[4] Staahl C, Dimcevski G, Andersen SD, Thorsgaard N, Christrup
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[5] Ross FB, Smith MT. The intrinsic antinociceptive effects of
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[7] Ross FB, Wallis SC, Smith MT. Co-administration of sub-antinociceptive doses of oxycodone and morphine produces marked antinociceptive synergy with reduced CNS side-effects in rats. Pain. 2000 Feb;84(2-3):421-8
[8] Blumenthal S, Min K, Marquardt M, Borgeat A. Postoperative intravenous morphine consumption, pain scores, and side effects with perioperative oral controlled-release oxycodone after lumbar diskectomy. Anesth Analg 2007;105:233-7
[9] http://www.qrxpharma.com/go.cfm?do=Page.View&pid=35 accessed 7.1.2010
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