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Anesth Analg 2005;101:812-818
© 2005 International Anesthesia Research Society
doi: 10.1213/01.ane.0000166982.19796.ae

PAIN MEDICINE

Long-Term Changes in the Antinociceptive Potency of Morphine or Dexmedetomidine After a Single Treatment

Gyongyi Horvath, MD PhD*{dagger}, Gabriella Kekesi, PhD*, Ildiko Dobos*, Walter Klimscha, MD{ddagger}, and Gyorgy Benedek, MD, DSc*

Departments of *Physiology, Faculty of Medicine, and {dagger}Physiotherapy, Faculty of Health Sciences, University of Szeged, Hungary; and {ddagger}Department of Anesthesia and Intensive Care, Danube Hospital, Vienna, Austria

Address correspondence to Gyongyi Horvath, Department of Physiology, Faculty of Medicine, University of Szeged, P.O. Box 427, H-6701, Szeged, Hungary. Address e-mail to horvath{at}phys.szote.u-szeged.hu.

Acute tolerance develops after a single administration of opiate or {alpha}2-adrenergic agonists, but the characteristics of the delayed type of acute tolerance have not been analyzed in acute and inflammatory thermal pain tests. We investigated the long-term changes in the antinociceptive potency of morphine (10 mg/kg) injected intraperitoneally and the {alpha}2-adrenoceptor agonist dexmedetomidine (150 µg/kg intraperitoneally) on acute heat pain (tail-flick test) sensitivity and on carrageenan-induced inflammatory thermal hyperalgesia (paw withdrawal test) after a second injection 7 days later. The first treatment did not influence the baseline values on Day 8 in either test. In the tail-flick test, the antinociceptive potency of morphine, but not that of dexmedetomidine, was significantly decreased after repeated administration, suggesting a delayed type of acute tolerance to morphine. In contrast, the antihyperalgesic effect of morphine in the paw withdrawal test did not change after repeated injection, whereas the potency of dexmedetomidine was increased on Day 8. There were significant differences between the inflamed and noninflamed sides on Day 1 but not on Day 8, revealing an increased potency of the drugs on the inflamed side. There was no sign of cross-tolerance between the two drugs in either pain test. These data indicate long-term changes in the antinociceptive potency of morphine or dexmedetomidine after single treatment in different heat pain tests.






Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press
Copyright © 2005 by the International Anesthesia Research Society.