Abstract

Since medetomidine and atipamezole first were used in non-domestic species in Finland and Sweden, more than 10 years have passed. Publications from all over the world on the use of these compounds in zoo and wild animals are numerous. Domitor® (medetomidine 1 mg/ml) and Antisedan® (atipamezole, 5 mg/ml) first became available on the U.S. market in October 1996. Most researchers have had access to a concentrated solution of medetomidine (now available in some countries as Zalopine®, 10 mg/ml), and have used relatively high doses of it. These publications, therefore, will be of limited value to the North American veterinarians as long as only Domitor® is available. Some dosages and practical tips on how to improve the immobilization and anesthesia in zoo and wild animals with the use of low concentrations of medetomidine are provided here.

Materials and Methods

Tiletamine and zolazepam became available in Scandinavia in 1990, initially as Telazol® (Fort Dodge) and since 1993 as Zoletil® (Laboratories Reading, F-06516 Carros); these products have primarily been used in wildlife species such as brown bear (Ursus arctos arctos), Baltic grey seal (Halichoerus grypus), and wild boar (Sus scrofa). From 1987 to 1990, approximately 140 bears were immobilized with medetomidine in combination with reduced doses of ketamine (MK) in association with the Scandinavian Brown Bear Project. The extremely quick and unforeseen recovery after these MK combinations caused a number of unpleasant situations. Since 1990, Telazol® has been used on brown bears at the doses used by North American scientists (i.e., 8–10 mg/kg). Though effective and safe, the disadvantages with the long and sometimes stormy recovery period prompted us to try to combine medetomidine with tiletamine + zolazepam (MTZ) in 1991.

In 1994 the use of etorphine in Sweden was limited to zoo and wildlife projects, even though over 10,000 farmed fallow and red deer had been successfully immobilized with a standard combination containing etorphine + xylazine (EX) in a ratio of 1:40 since 1975. In the exotic farmed species, the demand arose to find an effective and inexpensive non-opioid combination. Studies have been conducted with MK, xylazine + ketamine ([XK]; Hellabrunner Mischung), MTZ, xylazine with tiletamine + zolazepam (XTZ), and most recently with medetomidine or xylazine + butorphanol. In the veterinary work at the Kolmarden Zoo, medetomidine and atipamezole were introduced for clinical evaluation in 1986. The introduction of Telazol® and Zoletil® (TZ) took place in 1991. The use of MK and XK-mixtures were routine and the “new” TZ-products initially were used to replace ketamine in large carnivore species.

Results with MTZ in 450 Zoo and Wild Animals

Experiences using TZ in combination with medetomidine or xylazine indicate that the dosages of TZ given in USA literature could be significantly reduced when combined with xylazine and especially with medetomidine. By using Domitor® instead, as the solvent for Telazol®, a potent and stable mixture (MTZ) containing 1 mg medetomidine, 50 mg tiletamine, and 50 mg zolazepam/ml is achieved. This relationship between medetomidine and TZ (1:100) has been found to be clinically satisfactory, reversible, and relatively affordable in zoo species such as chimpanzee, lynx, brown bear, polar bear, wild boar, fallow deer, ostrich, Nile crocodile, and American alligator. A relatively increased dose of medetomidine (1:25–50) has been used in species such as lion, tiger, wolf, grey seal, fur seal, capybaras, domestic pig, and axis deer. This use provides the possibility to reverse the immobilization with atipamezole with only minimal residual effect of TZ, thus avoiding excitement and risk for injuries. In the species mentioned above, an M:TZ ratio of 1:100 would also work fine, but a quick and smooth recovery would be possible only soon before spontaneous recovery by the reversal of medetomidine with atipamezole. The cost and volume increase by adding medetomidine above the optimal 1:100 ratio.

Mortalities

Experiences with MTZ-mixtures have been most successful for immobilizations of 240 wild brown bears; no mortalities occurred. Of the 210 immobilizations in 18 zoo species (Table 1), two mortalities occurred. One large female chimpanzee with a chronic fibrinous pleuritis suffocated in a sitting position during the 25 minutes before it could be handled. One young 30 kg male axis deer immobilized with M 0.03+TZ 1 mg/kg, died in sternal position with bronchi and trachea filled with foamy fluid and no other lesions that would indicate overexertion or stress could be observed. In 10% of young axis deer, respiration suddenly has stopped. After doxapram, 1–2 mg/kg IV, and some initial external chest compressions, they have all recovered normally. No pulse oximetry has been carried out in axis deer. In other species, the MTZ combinations have been uneventful, and in primates and carnivores pO₂ between 85–97% has been found.

Table 1. Recommended dosages of M+TZ in some zoo species. The doses are based on the subjective experiences during routine clinical zoo veterinary work in Kolmarden Zoo 1991–1997

Documentation:
1-Low reliability, few or inconsistent immobilizations
2-Consistent but relatively few immobilizations
3-High reliability due to numerous and consistent results
Dosage in mg/kg:
M=medetomidine
TZ=tiletamine/zolazepam

Practical Recommendations in Zoo and Farmed Animals

When compared with published dosages of Telazol® in zoo animals, these dosages might be reduced by at least 50% by adding medetomidine at 1 mg/100 mg of Telazol®. This corresponds to 10 to 40 µg/kg of medetomidine in most zoo species. The mixture seems to be potent and safe for several weeks. The immobilization can, after 30–40 minutes, be reversed by atipamezole administered at a 5:1 ratio to medetomidine. If atipamezole is administered earlier, the animal is still sedated, immobilized, and/or excited by the Telazol®. If administered intramuscularly after more than 30–40 minutes of immobilization, most species will have a smooth recovery within 15 minutes. If the animal must be immobilized longer than 40–50 minutes, more anesthetics, either ketamine, 2 mg/kg, or Telazol®, at half initial dose, should be administered.