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Anesthetic Pharmacology
Anesthesia and Pain Medicine 2008;3(3):167-171.
Published online July 30, 2008.
The Cannabinoid Agonist WIN55,212-2 Suppresses Opioid-induced Pruritus in Mice
Heeseung Lee
Department of Anesthesiology and Pain Medicine, School of Medicine, Ewha Womans University, Seoul, Korea.
Cannabinoid receptor agonists can reverse opioidinduced nausea and vomiting in animals, but have not yet been tested against opioid-induced pruritus. This study tests the hypothesis that a cannabinoid receptor agonist will prevent opioidinduced pruritus and evaluates if the use of a cannabinoid receptor agonist will increase the analgesic efficacy of opioids. METHODS: Various doses of fentanyl were injected subcutaneously in mice to obtain a dose-response curve with the use of a writhing test. To observe the analgesic potentiation of the cannabinoid agonist WIN55,212-2 in the writhing test, mice were pretreated with various concentrations of WIN55,212-2 (0.25, 0.5, 1.0, 2.0 mg/kg) 10 min prior to the injection of an ED50 dose of fentanyl, as determined from the dose-response curve. To observe the antipruritogenic effect of WIN55,212-2 in a scratching test, mice were pretreated with WIN55,212-2 (0.25, 0.5 mg/kg) 20 min prior to fentanyl injection. A CB1 receptor selective antagonist, AM251 (3 mg/kg), was used to confirm the cannabinoid receptor selectivity. RESULTS: The ED50 of fentanyl in the writhing test was 0.018 mg/kg (range, 0.011?0.025 mg/kg). A dose of 1 mg/kg WIN55,212-2 increased the analgesic efficacy of fentanyl significantly (P < 0.001), but doses of 0.25 mg/kg and 0.5 mg/kg did not increase the analgesic efficacy. A dose of 0.25 mg/kg WIN55,212-5 reduced the scratching response of fentanyl significantly (P < 0.001) and this action was a cannabinoid receptor selective response. CONCLUSIONS: These results demonstrate that 0.25 mg/kg WIN55,212-2 can prevent opioid-induced pruritus. The antipruritogenic activity of WIN55,212-2 occurs at CB1 receptors even if the analgesic efficacy of fentanyl cannot be increased.
Key Words: cannabinoid, fentanyl, opioid, pruritus, WIN55,212-2
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