Effects of medetomidine on the experimental auricular pain in dogs

The analgesic effect of medetomidine was studied in ten laboratory beagles. The doses of medetomidine used were 10, 30 and 80 micrograms/kg BW. Xylazine (3 mg/kg BW) was included as a positive control and placebo as a negative control. The test utilized two independently randomized Latin square designs (5 x 5) and was carried out in a double blind fashion. Noxious stimuli were induced with a round pointed thermal probe which was set to produce a temperature of +44.9 +/- 0.2 degrees C. The wall of the external auditory canal was touched with the heated point of the probe. The time period from the start of the attachment to the avoidance reflex was measured and recorded as response time. To avoid tissue damage the heat treatment was stopped after 5 s even though the dog did not respond. Medetomidine clearly prolonged the response time. At the highest dose of medetomidine (80 micrograms/kg) all dogs reached the analgesic stage where they did not respond to the heat treatment. At 30 micrograms/kg of medetomidine half of the dogs had a prolonged response time. The lower dose of 10 micrograms/kg had no appreciable effect. Xylazine-induced analgesia was comparable to that of 30 micrograms/kg of medetomidine: half of the dogs lost their avoidance reflex. In conclusion, medetomidine proved to have a dose dependent analgesic effect in experimental auricular pain in dogs.