title: Naloxone blockade of morphine analgesia: a dose-effect study of duration and magnitude.
abstract: The purpose of the experiment was to determine the minimal dose of naloxone needed to block the analgesic effect of morphine as measured by the foot-shock titration procedure in the rat. Various groups of rats received, subcutaneously, various doses of naloxone hydrochloride, from 0.03 to 2.0 mg/kg, 15 minutes before receiving 10 mg/kg of morphine sulfate. The results indicate that 1.0 mg/kg of naloxone is the minimum dose necessary to provide full blockade of the measured morphine effect for up to 5 hours after the morphine administration. Partial blockade was evident at doses much smaller than 1.0 mg/kg of naloxone. A dose of 0.125 mg/kg of naloxone completely blocked the onset of a measurable effect from 10 mg/kg of morphine for 60 minutes in six out of the seven animals tested at that dose. The results provide a clear dose-effect relationship for both magnitude and duration of naloxone blockade of the analgesic effect of morphine.
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004597:Electroshock; D007279:Injections, Subcutaneous; D008297:Male; D009020:Morphine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D013997:Time Factors
chemical_list: D009270:Naloxone; D009020:Morphine