The analgesic effect of buprenorphine, etorphine and pethidine in the pig: a randomized double blind cross-over study.

In order to find a suitable analgesic for the treatment of postoperative pain in pigs the analgesic effect of buprenorphine, etorphine and pethidine has been compared in 8 domestic pigs. For assessment of the analgesic action on thermal (hot plate) and two mechanical (cannulation of ear vein, needle prick) noxious stimuli have been employed. In a pilot experiment on 2 pigs in which methadone was included the maximal effective doses were estimated for each drug. Methadone was found unsuitable because of unacceptable side effects (respiratory dysfunction, hyperactivity) at effective dose levels. Next buprenorphine 120 micrograms/kg, etorphine 3 micrograms/kg and pethidine 20 mg/kg all given intramuscularly were compared in a randomized blind trial with a balanced cross-over design on 6 pigs. Etorphine proved to have the highest and pethidine the lowest maximal analgesic effect which was especially evident in the needle-prick test. Buprenorphine proved to have the longest duration of action in all three analgesic tests, in the hot plate test lasting between 7 and 24 hrs. Etorphine had a duration of 3 to 5 hrs whereas the effect of pethidine was short, only lasting about 2 hrs. Etorphine provides a complete analgesia but has a small safety margin for which reason it should be used with caution in the pig. The experimental results indicate that buprenorphine should be the first drug of choice in the treatment of pain after surgical intervention due to its long duration of action and lack of side effects.