Comparison of the effects of epidural or intravenous methadone on the minimum alveolar concentration of isoflurane in dogs

The effects of epidural and intravenous (IV) methadone (0.5mg/kg) on the minimum alveolar concentration of isoflurane (ISOMAC) were compared in dogs. Six dogs (16.5±2.5kg bodyweight) received three treatments in random order during isoflurane anaesthesia, with a 7day washout interval between each study. Methadone was injected via a lumbosacral epidural catheter introduced 10cm cranially into the epidural canal and the electrical stimulation for ISOMAC determination was applied either to the thoracic (EPT treatment) or to the pelvic limb (EPP treatment) during separate study days. In the IV treatment, ISOMAC was determined via electrical stimulation of the pelvic limb. Variables were recorded before (baseline), 2.5 and 5h after drug injection. The ISOMAC decreased significantly (P