In recent years, various combinations of drugs have been used for anesthesia of bear species in zoo and wildlife applications. Medetomidine and ketamine have both been associated with the risk of spontaneous arousal during anesthesia.1,7 Tiletamine and zolazepam (Telazol, Fort Dodge Animal Health, Fort Dodge, IA, USA) has no antagonist available for the tiletamine component and has been associated with prolonged recovery times.1,6 A combination of medetomidine and tiletamine/zolazepam (MZT) has been used in several bear species successfully2,3,8 with minimal adverse physiologic effects. Although this combination has been successful for immobilizing bear species at the Calgary Zoo, particularly in grizzly bears (Ursus arctos), polar bears, and spectacled bears it has resulted in prolonged recovery times with up to 4 hours of heavy sedation after reversal of the medetomidine with atipamezole (Antisedan, Novartis Animal Health Canada, Mississauga, ON, Canada).
Since 2001, four of the five species of bear housed at the Calgary Zoo have been immobilized with a combination of medetomidine (Zalopine, Orion Pharmaceuticals, Corporation, Espoo, Finland; 0.035–0.075 mg/kg IM), ketamine (Parke-Davis division, Pfizer Canada, Inc., Kirkland, QC, Canada; 2.5–4.0 mg/kg IM), and midazolam (Sabex, Boucherville, QC, Canada; 0.05–0.09 mg/kg IM) (MMK). All bears were administered atipamezole (0.119–0.189 mg/kg, half IM, half SC) at the conclusion of the immobilization procedure. There has been a total of 14 immobilizations in nine individuals. This combination is similar to MZT, using a dissociative anesthetic agent (ketamine) with a benzodiazepine tranquilizer (midazolam) and an alpha-2 agonist (medetomidine). The primary difference between the two combinations is the ability to alter the ratio between the dissociative and the benzodiazepine with MMK. Midazolam has a mean elimination half-life of 77±18 minutes in dogs, making it an ideal benzodiazepine to use in anesthetic protocols for short procedures in carnivores.4 Induction times using MMK in ursid species were 12.1±2.12 minutes (range 9–15 minutes), with times to full recovery ranging from 20 minutes to 1 hour, with a single exception of a black bear exhibiting a 2-hour recovery to a normal appearance. Initial average heart rates were 59±29 bpm (range 27–118 bpm). Initial oxygen saturation measurements were 86.14±4.64% (range 76–93%) before supplemental oxygen was provided, and over 90% in all bears with supplemental oxygen. Similar to the satisfactory results produced using MMK in Siberian tigers (Panthera tigris altaica),5 MMK shows good promise to be an effective and safe immobilizing drug combination for bear species, with short induction and recovery times and little risk of spontaneous arousal.
1. Cattet, M.R.L., N.A. Caulkett, S.A. Polischuk and M.A. Ramsay. 1999. Anesthesia of polar bears (Ursus maritimus) with zolazepam-tiletamine, medetomidine-ketamine and medetomidine-zolazepam-tiletamine. J Zoo Wildl Med. 30(3):354–360.
2. Cattet, M.R.L., N.A. Caulkett, S.A. Polischuk, and M.A. Ramsay. 1997. Reversible anesthesia of free ranging polar bears with medetomidine-zolazepam-tiletamine and atipamezole. J Wildl Dis. 33(3):611–617.
3. Caulkett, N.A., and M.R.L. Cattet. 1997. Physiological effects of medetomidine-zolazepam-tiletamine immobilization in black bears. J Wildl Dis. 33(3):618–622.
4. Court, M.H., and D.J. Greenblatt. 1992. Pharmacokinetics and preliminary observations of behavioral changes following administration of midazolam to dogs. J Vet Pharmacol Ther. 15(4):343–350.
5. Curro, T.G., D. Okeson, D. Zimmerman, D.L. Armstrong, and L.G. Simmons. 2004. Xylazine-midazolam-ketamine versus medetomidine-midazolam-ketamine anesthesia in captive Siberian tigers (Panthera tigris altaica). J Zoo Wildl Med. 35(3):320–327.
6. Haigh, J.C., I. Stirling, and E. Broughton. 1985. Immobilization of polar bears (Ursus maritimus, Phipps) with a mixture of tiletamine and zolazepam hydrochloride. J Wildl Dis. 21(3):43–47.
7. Jalanka, H.H., and B.O. Roeken. 1990. The use of medetomidine, medetomidine-ketamine combinations and atipamezole in nondomestic mammals: a review. J Zoo Wildl Med. 21(3):259–282.
8. Onuma, M. 2003. Immobilization of sun bears (Helarctos malayanus) with medetomidine-zolazepam-tiletamine. J Zoo Wildl Med. 34(4):202–205.