Abstract

Tiletamin-zolazepam (TZ) is the drug of choice for immobilization of brown bears (Ursus arctos), black bears (U. americanus), and polar bears (U. maritimus).^4,5 Effective doses in free-ranging individuals are 7–9 mg/kg.^4,6,7 TZ has a wide margin of safety, and has no major cardiopulmonary or thermoregulatory side effects in bears.^3,6-8 The main disadvantage of TZ is extended recoveries. There is no reversal agent for tiletamine, and the use of a benzodiazepine antagonist in animals immobilized with high doses of TZ is not recommended. However, in combination with medetomidine (M), the effective dose of TZ in polar bears can be reduced by as much as 75%, and atipamezole (A) can then be used to shorten the recoveries.¹ The physiologic effects of MTZ have been studied in polar bears and black bears, and this drug combination is well tolerated by healthy individuals.^2,3 The purpose of the present study was to evaluate MTZ and A for reversible immobilization and anesthesia of free-ranging brown bears in Scandinavia.

During an 8-year-period, 1993–2000, a total of 575 captures of 241 individual free-ranging brown bears were accomplished in Sweden and Norway with combinations of M (Domitor® 1 mg/ml or Zalopine® 10 mg/ml, Orion Pharma Animal Health, Turku, Finland) and TZ (Zoletil® 500 mg dry powder/vial, Virbac International, Carros Cedex, France). The bears were captured for radio tagging, biometry, and biologic sampling as part of an ongoing ecologic and demographic study on Scandinavian brown bears. Bears were darted from a helicopter using DAN-INJECT® equipment (DAN-INJECT ApS, Børkop, Denmark). Captures were made during spring and early summer (April-June). All bears received 5 mg A (Antisedan® 5 mg/ml, Orion Pharma Animal Health) per mg M, administered half IV and half SC or half IM and half SC, for reversal.

Analyses of drug doses and induction times were carried out for 342 (59.5%) of the 575 capture events, including only animals that were completely immobilized for at least 40 minutes after a single dart injection and that did not require additional dosing during this period of time, and excluding animals that were not observed going down (n=28) and animals that could not be weighed (n=25). Mean induction times varied from 3.3 to 6.5 min for different classes of bears. Summary statistics are presented in Table 1. The bears were grouped in three age classes: 1-year-old, 2-year-old, and adults (animals=3 year). A t-test (two-sample, two-tailed, unequal variance) was used to compare males and females in each age class, and p-values <0.05 was considered significant. No significant gender difference were found for 1-year-old bears, and data for females and males were pooled. In 2-year-old bears, females received significantly higher drug doses than males. However, there was no significant difference in induction time. In adults, the induction time was significantly longer for males than for females, although there was no significant difference in drug doses.

Table 1. Summary of drug doses and induction times in free-ranging Scandinavian brown bears (Ursus arctos) immobilized for at least 40 minutes after one single dart injection with medetomidine (M) and tiletamine-zolazepam (TZ) 1993–2000, data are given as mean ± SD

^aNumber of immobilizations.
^bDomitor 1 mg/ml or Zalopine® 10 mg/ml (Orion Pharma Animal Health, Turku, Finland).
^cZoletil® 500 mg dry powder/vial (Virbac International, Carros Cedex, France).
^dPooled data for males and females.
^eAnimals, 3 years old.

A total of 72 surgical implantations of intraperitoneal radio transmitters (Telonics Inc., Meza, AZ, USA) were performed under MTZ anesthesia in 70 individual bears (35 1-year-old females, 20 1-year-old males, 6 2-year-old females, 10 adult females, and 1 adult male). Muscle relaxation was good, and depth of anesthesia was adequate for surgery. Two animals, a 2-year-old female and a 7-year-old female with yearling cubs, underwent a second surgery after 1 and 3 years, respectively, in order to change the implant. No pathologic lesions caused by the initial surgery or implant were seen in these individuals.

Three bears (0.5%) died during immobilization. None of these animals were undergoing surgery. Necropsies showed cardiovascular and respiratory collapse as the primary cause of death in a 2-year-old male in poor body condition (33 kg; 0.095 mg M/kg + 11.9 mg TZ/kg total drug dose). In a 1-year-old female (21 kg; 0.031 mg M/kg + 3.1 mg TZ/kg) and a 3-year-old male (101 kg; 0.020 mg M/kg + 2.5 mg TZ/kg) severe hemorrhagic enteritis was found, but no specific infectious agent was isolated.

Rectal temperature was measured in all bears. In addition, animals undergoing surgery were monitored by use of pulse oximetry. Physiologic data will be presented elsewhere. Due to time constraint and logistics, data on recovery from anesthesia were collected only during the initial phase of this study. However, each bear was located the same day to ensure that the animal had moved away from the capture site. Radiotracking revealed no mortalities related to the capture event or the surgical intervention. No permanent separation of family groups (female with yearling cubs) occurred.

During the course of this study, standard immobilizing doses of MTZ for various age and sex classes were established. The following recommendations are currently applied: 0.5 mg M plus 125 mg TZ in 1-year-old bears (15–45 kg); 1 mg M plus 250 mg TZ in 2-year-old and 3-year-old bears (45–70 kg); 2 mg M plus 500 mg TZ in adult females and subadult males (70–120 kg); 3 mg M plus 750 mg TZ in small adult males (120–180 kg); 4 mg M plus 1000 mg TZ in large adult males (180–240 kg). If the bear is not down in 15 minutes, a full dose is repeated. All bears are receiving 5 mg A per mg M, administered half IM and half SC, for reversal.

In conclusion, medetomidine-tiletamine-zolazepam is an excellent drug combination for immobilization and anesthesia of free-ranging Scandinavian brown bears. Induction is rapid, the safety margin is wide, there are no major adverse clinical effects, muscle relaxation is good, and analgesia is adequate for abdominal surgery. By use of atipamezole the recovery times can be shortened.

Acknowledgments

Generous supplies of drugs for parts of this study were received from Orion Pharma Animal Health (Domitor®, Zalopine®, and Antisedan®) and Boehringer Ingelheim Vetmedica AS (Zoletil®).

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