Fentanyl and medetomidine anaesthesia in the rat and its reversal using atipamazole and either nalbuphine or butorphanol

Abstract

The intraperitoneal injection of anaesthetic agents is a simple and convenient method of anaesthetizing rats. However, all of the anaesthetic combinations in current use which are administered by intraperitoneal injection produce prolonged sedation, and full recovery of consciousness may take several hours. Fentanyl, a μ agonist opioid, and medetomidine, an α2-adrenoceptor agonist were mixed and administered as a single intraperitoneal injection. Combinations of 300 μg/300 μg/kg and 300 μg/200 μg/kg of fentanyl/medetomidine were shown to produce surgical anaesthesia in the rat. This anaesthetic regimen produced significant respiratory depression ( P<0.01) and animals did not regain their righting reflex until 193±21 min (mean±1 SD) after injection. Administration by intraperitoneal injection of atipamezole, a specific α2-adrenoceptor antagonist (1 mg/kg) mixed with a μ antagonist/k agonist opioid (nalbuphine, 2 mg/kg or butorphanol 0·4 mg/kg), resulted in a rapid (<8 min) reversal of anaesthesia and the associated respiratory depression, and apparent full recovery of consciousness.