ABSTRACT
Pain management in reptiles is poorly understood and most published reptile opioid doses are empirically derived. In this study, five adult (3 male, 2 female) green iguanas, Iguana iguana, were given either 0.5 ml saline or an opioid analgesic agent intramuscularly 30 min prior to electrostimulation of the tail to compare responses. Opioid analgesic agents evaluated were butorphanol at 0.4, 1.5, 4.0 and 8.0 mg/kg, buprenorphine at 0.02 and 0.1 mg/kg, and morphine at 0.4 and 1.0 mg/kg. Electrostimulation was administered with a Grass stimulator® with the two electrodes placed 1 cm apart at the measured junction of the first and second thirds of the tail, randomly delivering currents of 2, 10, 20 and 40 mA for a duration of 500 mS, 10 min apart. The iguanas' responses were recorded on videotape so three evaluators, blinded to the agent given, could determine a score (0–20) based on a response scale developed for this study. Increasing scores correlated with increases in heart rate, and movement of the head, eye, body and tail. Body movement response scores were significantly (P<0.05) lower at all currents for morphine at 1.0 mg/kg and for butorphanol at both 1.5 and 8.0 mg/kg, when compared to saline. There was no significant difference in body movement response scores between saline and butorphanol at 0.4 and 4.0 mg/kg, buprenorphine at 0.02 and 0.1 mg/kg and morphine at 0.4 mg/kg. These results indicate that antinociception is provided in green iguanas from morphine at 1.0 mg/kg IM, or butorphanol at 1.5 mg/kg or 8.0 mg/kg IM and that these drugs, at these dosages, would be expected to provide analgesia to green iguanas in a clinical setting. Electrostimulation of the tail provided a good model of antinociception for use in further research on analgesia in green iguanas.
