TECHNIQUE

Medetomidine-Tiletamine-Zolazepam Anaesthesia in Bears (Disease Investigation & Management - Treatment and Care)

Summary Information
Type of technique Health & Management / Disease Investigation & Management / Techniques:
Synonyms and Keywords See also:
Description Note: medetomidine doses are mainly given in microgrammes per kilogram bodyweight, indicated in the text below as "g/kg". Other drug doses are generally given in milligrams per kilogram bodyweight (mg/kg).

N.B. Information given in this page is to be used in conjunction with the relevant section on Bears in Treatment and Care - Anaesthesia and Chemical Restraint

Preparation for anaesthesia:

  • Whenever possible (with captive bears), the bear should be moved to a safe, quiet, well-controlled situation away from other bears. (B407.w18, D247.7.w7)
  • Avoid anaesthetising immediately after the bear has eaten, to reduce the risks associated with vomiting and regurgitation during induction, anaesthesia or recovery. (D156.w2)
    • Preferably starve for 24 hours before anaesthesia. (B407.w18)
    • Withhold water for eight hours and food for 24 hours before immobilization. (D247.7.w7)

Administration:

  • By intramuscular injection, with the drugs in a single syringe. (J1.33.w16, J1.33.w17, P504.2001.w5)
  • Usually administered by remote injection (darting) (J1.33.w16, J1.33.w17, P504.2001.w5) or if the bear is in a confined space, by pole syringe. (J2.30.w6, P20.1998.w10)
  • For cubs under one year of age, by hand injection or pole syringe. (J1.33.w17)
  • See: Intramuscular Injection of Bears

Suggested doses:

  • Helarctos malayanus - Sun bear
    • Medetomidine 50.0 g/kg, Tiletamine-Zolazepam 2.0 mg/kg, in bears at a wildlife rehabilitation centre in Malaysia, provided effective immobilization, good muscle relaxation and minimal cardiovascular effects. (J2.34.w4)
    • For bears rescued from bear bile farms, 0.01 mg/kg Medetomidine plus 1.0 mg/kg Tiletamine-Zolazepam, by intramuscular injection. (V.w90)
      • This provides Stage 2/Stage 3 anaesthesia for about 30-45 minutes, allowing physical examination or minor surgical procedures such as wound treatment, skin biopsy and castration. (V.w90)
      • For longer and/or more invasive procedures, anaesthesia is prolonged with inhalant anaesthesia.
      • The medetomidine is reversed with atipamezole. (V.w90)
  • Ursus americanus - American black bear: 
  • Ursus arctos - Brown bear
    • Medetomidine 0.06 mg/kg, Tiletamine-zolazepam 2 mg/kg. (B345.6.w6, B336.51.w51)
    • Medetomidine 35 g/kg, Tiletamine-zolazepam 4.8 mg/kg. (D156.w2)
    • For zoo bears medetomidine 0.01 mg/kg plus tiletamine-zolazepam 1.0 mg/kg or medetomidine 0.03 mg/kg plus tiletamine-zolazepam 0.5 mg/kg. (P1.1997.w9)
    • For free-ranging brown bears in Scandinavia:
      • 20-30 kg: medetomidine 0.04 mg/kg + tiletamine-zolazepam 5.0 mg/kg. (P1.1997.w9)
        • or for 1.5 year-old cubs, darts containing medetomidine 1 mg plus tiletamine-zolazepam 125 mg. (P1.1997.w9)
      • 40-60 kg: medetomidine 0.02 mg/kg + tiletamine-zolazepam 5.0 mg/kg. (P1.1997.w9)
        • or for 2.5-year-old bears darts containing medetomidine 1 mg plus tiletamine-zolazepam 250 mg. (P1.1997.w9)
      • 80-140 kg: medetomidine 0.02 mg/kg + tiletamine-zolazepam 4.0 mg/kg. (P1.1997.w9)
        • or for adult female bears darts containing medetomidine 2 mg plus tiletamine-zolazepam 500 mg. (P1.1997.w9)
      • 200-250 kg: medetomidine 0.015 mg/kg + tiletamine-zolazepam 3.0 mg/kg. (P1.1997.w9)
        • or for adult male bears darts containing medetomidine 2.5 mg plus tiletamine-zolazepam 750 mg. (P1.1997.w9)
    • For free-ranging brown bears in Sweden and Europe, based on 575 immobilisations of 241 individual bears, the following have been recommended: (P504.2001.w5)
      • Yearlings, 15-45 kg bodyweight: 0.5 mg medetomidine + 125 mg tiletamine-zolazepam. 
      • Two-year-olds and three-year-olds, 45-70 kg bodyweight: 1 mg medetomidine plus 250 mg tiletamine-zolazepam. 
      • Adult females and subadult males, 70-120 kg: 2 mg medetomidine plus 500 mg tiletamine-zolazepam. 
      • Small adult males 120-180 kg: 3 mg medetomidine plus 750 mg tiletamine-zolazepam. 
      • Large adult males: 180-240 kg: 4 mg medetomidine plus 1,000 mg tiletamine-zolazepam.
      • All bears, if the bear is not recumbent after 15 minutes, repeat the full dose. (P504.2001.w5)
    • For bears rescued from bear bile farms, 0.01 mg/kg medetomidine plus 1.0 mg/kg tiletamine-zolazepam, by intramuscular injection. (V.w90)
  • Ursus maritimus - Polar bear:
    • Medetomidine 75 g, Tiletamine-zolazepam 2.2 mg/kg. (D156.w2)
    • Medetomidine 34-225 g/kg, tiletamine-zolazepam 1.14-7.43 mg/kg. (J2.30.w5)
    • Medetomidine 74.8 +/- 11.8 g/kg medetomidine + 2.2 +/- 0.3 mg/kg tiletamine-zolazepam. (J2.30.w6)
    • Medetomidine 60 g/kg plus tiletamine-zolazepam 2.0 mg/kg (1.0 mg/kg each) intended dose; actual medetomidine mean 70 g/kg (median 64 g/kg), tiletamine-zolazepam mean 2.3 mg/kg (median 2.1 mg/kg) for bears requiring only one dose for immobilization. (J1.33.w17)
    • Medetomidine 0.01 mg/kg plus tiletamine-zolazepam 1.0 mg/kg OR medetomidine 0.015 mg/kg plus tiletamine-zolazepam 0.5 mg/kg. (P1.1997.w9)
    • Medetomidine mean 74.8 +/- 11.8 g/kg, tiletamine-zolazepam mean 2.2 +/- 0.3 mg/kg (intended dose estimated medetomidine 52 g/kg plus tiletamine-zolazepam 0.86 mg/kg). (P20.1998.w10)
  • Ursus thibetanus - Asiatic black bear:
    • For bears rescued from bear bile farms, 0.01 mg/kg medetomidine plus 1.0 mg/kg tiletamine-zolazepam, by intramuscular injection. (V.w90)

During induction:

  • Ursus maritimus - Polar bear generally remained still during induction, slowly sinking to recumbency. (J2.30.w5)
  • Rapid, smooth induction in Ursus americanus - American black bear. (J1.33.w16)
  • Rapid induction: ranging from 3.3 +/- 1.9 minutes in yearling brown bears given 0.035 mg/kg medetomidine plus 4.8 +/- 1.7 mg/kg tiletamine-zolazepam, to 6.5 +/- 4.2 minutes in adult males given 0.020 +/- 0.007 mg/kg medetomidine and 4.7 +/- 1.8 mg/kg tiletamine-zolazepam. (P504.2001.w5)
  • Rapid induction in Ursus maritimus - Polar bears (mean 3.6 minutes, median 3.1 minutes, for bears requiring only one dose for immobilization); bears usually stopped running, stood still, then sat back and slowly dropped to sternal recumbency. (J1.33.w17)
  • Ursus maritimus - Polar bears were immobilised in 3.7 +/- 2.7 minutes (mean +/- SD). (P20.1998.w10)
  • In 22 anaesthetics of 16 Helarctos malayanus - Sun bears (six immobilized twice) at a wildlife rehabilitation centre in Malaysia, seven bears vomited during induction. With a dose of 50.0 g/kg medetomidine and 2.0 mg/kg tiletamine-zolazepam, initial effects (ataxia or sedation) were noted after 31 +/- 1.1 minutes (range 1.9 - 5.3 minutes) and complete immobilization was achieved after 7.6 +/- 3.7 minutes (range 2.8 - 16.0 minutes). (J2.34.w4)

During anaesthesia:

  • Good muscle relaxation, no muscle rigidity. (J1.33.w16, (J1.33.w17), J2.30.w5, P504.2001.w5)
  • Eyes remain in a fixed stare. (J2.30.w5)
  • No tongue withdrawal reflex, no jaw tone, no palpebral reflex, occasional nystagmus. (J1.33.w17)
  • Usually remain unresponsive to noxious stimuli. (J2.30.w5)
  • Remained unresponsive to noxious stimuli. (J1.33.w16)
  • Expect heart rates of about 50-70 beats per minute. (D156.w2)
  • Minimal cardiovascular effects. In Ursus americanus - American black bear given medetomidine 52 g/kg and tiletamine-zolazepam 1.72 mg/kg, at 30 minutes post injection, heart rate was 62 +/- 13 bpm, respiratory rate 11+-2 breaths per minute, mean arterial pressure 186 +/- 47 mmHg, rectal temperature 37.7 +/- 0.5 C, haemoglobin saturation 87 +/- 8 %, pH 7.3 +/- 0.03, PaCO2 44.5 +/- 6.5, Pa O2 72.4 +/- 9.9, base excess -3.9 +/- 1.6 (all mean +/- SD). Oxygenation was generally good, although one bear had transient hypoxaemia; ventilation was generally good but the same bear developed hypoventilation at 15 minutes post inoculation. The bears showed mild acidosis, probably respiratory acidosis, more pronounced in the bear with hypoventilation. Body temperature tended to increase slightly over time (by about 1 C over an hour, at an ambient temperature of 25 C. (J1.33.w16)
  • Analgesia is sufficient for abdominal surgery. (P504.2001.w5)
  • Ursus maritimus - Polar bears anaesthetised with this combination appeared to be in a "deeper" plane of anaesthesia than those immobilised with tiletamine-zolazepam alone. Analgesia was good, with no change in heart rate or blood pressure when a nail bed was compressed with haemostats. At 30 minutes after administration, heart rate was mean 46 +/-12 bpm, respiratory rate 6 +/- 2 breaths/minute, mean arterial pressure 228 +/- 24 mm Hg, rectal temperature 37.2 +/- 0.5 C, pH 7.27 +/- 0.02, base excess -5.1 +/- 0.8, Pa O2 62.9 mm HG and PaCO2 47 +/- 4 mmHg. Heart rate, respiratory rate, PaO2 and base excess were significantly lower than with tiletamine-zolazepam; arterial pressures (systolic, mean and diastolic) were significantly higher than with tiletamine-zolazepam. Bears were hypoxaemic with this combination; hypoxaemia was most severe at 15 minutes post administration, but were ventilating adequately as indicated by PaCO2. (P20.1998.w10)
  • In Helarctos malayanus - Sun bears at a wildlife rehabilitation centre in Malaysia, all bears developed effective immobilization for more than one hour, with adequate muscle relaxation and absent palpebral reflex. No side-to-side head movements were noted (this was a problem with tiletamine-zolazepam used alone). Rectal temperatures declined significantly, from mean 38.4 C at the time of first handling to 38.1 C by 20 minutes and 37.6 C by 40 minutes. Heart rate decreased significantly from mean 77 bpm at 0 and 10 minutes from first handling to 66 bpm by 30 minutes and 58 bpm by 40 minutes. Respiratory rates declined slightly (not significant) from mean 24 breaths per minute at first handling to 22 at 10 and 20 minutes and 16 by 40 minutes. (J2.34.w4)

Duration of anaesthesia:

  • Reversed after one hour in Ursus americanus - American black bear. (J1.33.w16)
  • Maintained anasethetised for three hours; 23 of 51 bears required a top-up doze of medetomidine at 100 minutes and six a further dose at 175 minutes, due to signs such as increasing nystagmus, increased withdrawal activity and increased jaw tone and movement; pulse and respiratory rate did not change. (J1.33.w17)
  • For bears (Ursus thibetanus - Asiatic black bear, Ursus arctos - Brown bear and Helarctos malayanus - Sun bear) rescued from bear bile farms, 0.01 mg/kg Medetomidine plus 1.0 mg/kg Tiletamine-Zolazepam, by intramuscular injection provides Stage 2/Stage 3 anaesthesia for about 30-45 minutes, allowing physical examination or minor surgical procedures such as wound treatment, skin biopsy and castration. (V.w90)
    • For longer and/or more invasive procedures, anaesthesia is prolonged with inhalant anaesthesia.
  • In Helarctos malayanus - Sun bears at a wildlife rehabilitation centre in Malaysia, with doses of 30-52 g/kg medetomidine plus 2.0-2.4 mg/kg tiletamine-zolazepam, the first signs of recovery occurred at 99.4 +/- 51.9 minutes (mean +/-SD) (range 40.0-183.3 minutes), with head up at 183.0 +/- 59.7 minutes (68.0-245.3 minutes) and the total immobilization time (time in lateral recumbency, unresponsive to noxious stimuli) was 189.2 +/- 51.9 minutes (40.0 - 250.5 minutes). (J2.34.w4)

Reversal with Atipamezole:

  • Atipamezole is usually given at five times the dose of medetomidine used. (B345.1.w1)
    • i.e. for this combination, with 0.06 mg/kg medetomidine given in Ursus arctos - Brown bear, 3.0 mg medetomidine is given for reversal. (B345.6.w6)
  • Atipamezole, four times the dose of medetomidine in g/kg, in Ursus americanus - American black bear, given half intravenously into the jugular vein, half intramuscularly into the neck muscles, gave recovery in 6.0 +/- 4.0 minutes (range 2-10 minutes). Bears appeared somewhat disorientated, probably due to the continuing action of tiletamine and zolazepam, but were able to leave the trap and walk off within an hour. (J1.33.w16)
  • Atipamezole at four times the dose of medetomidine given (mg per mg), half given intramuscularly, half intravenously.(P20.1998.w10)
  • Reverse with atipamezole at five times the dose of medetomidine given (mg per mg), half given intramuscularly, half intravenously. (P504.2001.w5)
  • Atipamezole given at 3-4 times the dose of medetomidine, either intravenously or half intravenously and half intramuscularly. (J1.33.w17)
  • Atipamezole, given at five times the medetomidine dose used, no sooner than 30-40 minutes after immobilization. (P1.1997.w9)
  • For bears (Ursus thibetanus - Asiatic black bear, Ursus arctos - Brown bear and Helarctos malayanus - Sun bear) rescued from bear bile farms and anaesthetised with 0.01 mg/kg Medetomidine plus 1.0 mg/kg Tiletamine-Zolazepam by intramuscular injection, the medetomidine is reversed with atipamezole. (V.w90)
  • In Helarctos malayanus - Sun bears at a wildlife rehabilitation centre in Malaysia, reversal with 250 g/kg atipamezole, given intravenously into the jugular vein after one hour, significantly reduced recovery time. The first signs of recovery occurred at 61.4 +/- 10.6 minutes (mean +/-SD) (range 33.0-72.4 minutes), with head up at 64.6+/-3.6 minutes (61.5-72.4 minutes) and the total immobilization time (time in lateral recumbency, unresponsive to noxious stimuli) was 81.7 +/-7.3 minutes (73.0-95.8 minutes). No re-sedation was seen. (J2.34.w4)

During recovery:

  • Signs of anaesthetic lightening include deep breathing, sighing, licking and development of a spontaneous palpebral. (D156.w2)
  • Head lifting or paw movement may indicate imminent arousal. (D156.w2)
  • Recovery following administration of atipamezole is usually smooth and occurs within 15 minutes. (P1.1997.w9)
  • Recovery after mean 2.4 minutes (median 2.5 minutes) in bears given the whole dose of atipamezole intravenously; for those give half the dose intravenously, half intramuscularly, recovery in mean 7.5 minutes (median 6.5 minutes). Usually well-coordinated, sometimes hind limb ataxia for 30-60 minutes. No re-sedation was recorded (bears observed usually for up to one hour after reversal). (J1.33.w17)
Appropriate Use (?)
  • For rapid, reliable, reversible anaesthesia with minimal adverse physiological effects. (J1.33.w16)
  • Short induction. (J1.33.w17, J2.30.w5, P504.2001.w5)
  • Small volume of drugs required. (J2.30.w5, J1.33.w16, J1.33.w17)
  • Reversible with atipamezole, reducing recovery time. (J1.33.w16, (J1.33.w17), P504.2001.w5)
  • Good analgesia. (J1.33.w17, P504.2001.w5)
  • Reliable. (J1.33.w17)
  • Safe for use by field personnel. (J1.33.w17)
Notes
  • Safe and reliable; no mortalities in 240 immobilisations of wild brown bears. ((P1.1997.w9))
  • If a longer period of anaesthesia (more than 40-50 minutes) is required, ketamine can be given at 2 mg/kg or tiletamine-zolazepam at half the initial dose. (P1.1997.w9)
  • Supplemental oxygen should be available. (P20.1998.w10)
Complications/ Limitations / Risk
  • Bradycardia and hypoxaemia was noted in Ursus maritimus - Polar bears. (P20.1998.w10)
  • During a study of 51 immobilizations of free-ranging polar bears, one individual's temperature rose during anaesthesia and, following injection of atipamezole, the bear developed prolonged (right minutes), intense convulsions, marked hyperthermia (42.6 C) and died. (J1.33.w17)
  • Five bears captured at ambient temperatures above 20 C required cold-water enemas during the period of anaesthesia to keep their rectal temperature below 39 C. (J1.33.w17)
  • If the medetomidine is reversed too early (after less than 30-40 minutes) the animal may still be sedated, immobilised and/or excited due to the effects of the tiletamine-zolazepam. (P1.1997.w9)
  • In Helarctos malayanus - Sun bears at a wildlife rehabilitation centre in Malaysia, vomiting occurred at induction or recovery in 16 of 22 immobilizations. (J2.34.w4)
  • Avoid loud noises; there are reports of bears partially waking under medetomidine anaesthesia. (D315.3.w3)
  • Physical injury, sometimes severe or even fatal, can occur when bears are darted, for example from darts which enter a body cavity instead of hitting muscle. (P9.2004.w4, J40.32.w1, D249.w10)
Equipment / Chemicals required and Suppliers
Expertise level / Ease of Use
  • Bears are large, powerful carnivores. Anaesthesia of bears should be carried out by experienced personnel. (V.w6)
Cost/ Availability
  • Cost and availability of drugs required may vary between countries.
Legal and Ethical Considerations
  • In some countries there may be legislation restricting the use of this type of technique to licensed veterinarians. For example in the UK: "The Veterinary Surgeons Act 1966 (Section 19) provides, subject to a number of exceptions, that only registered members of the Royal College of Veterinary Surgeons may practice veterinary surgery." (see: LCofC1 - RCVS Guide to Professional Conduct 2000 - Treatment of Animals by Non-Veterinary Surgeons).).

Use of Drugs (Medication):

  • Many drugs are not registered for use in particular species and care should be taken in their use, with proper regard for possible toxic effects. Consideration should be give to relevant legislation regarding the use of drugs.
  • In any country, drugs are unlikely to be specifically licensed for use in bears. 
    • In Europe the prescription cascade must be followed, and the client's informed consent should be obtained, whenever a drug is used which is not licensed for use in a given species. (B284.5.w5)
    • In the UK, guidelines regarding the use of drugs are set out in the Royal College of Veterinary Surgeons Guide to Professional Conduct 2000: (see: LCofC1 - RCVS Guide to Professional Conduct 2000 - Choice of Medicinal Products).
    • In the USA, the Food and Drug Administration (FDA) regulates specific conditions for the use of drugs in animals and people. The Animal Medicinal Use Clarification Act of 1996 allows extra-label use of approved animal and human drugs under certain conditions, with extra-label use being allowed "in non-food-producing animals if the drug is approved by the FDA, is used by or on order of a licenced veterinarian, and there is a valid veterinarian/client/patient relationship." In food-producing animals (including game wildlife species), additional conditions for extra-label use include that there is no approved alternative drug for such use (or if there is, it is clinically ineffective), the veterinarian has established a substantially extended withdrawal period; the treated animal can be individually identified (e.g. with an ear tag or a collar) and assigned withdrawal times can be assured, ensuring no illegal residues. (B486.11.w11)
  • Additionally, many drugs used for immobilisation are controlled substances in many countries, and appropriate registration/licences, records etc. for the country in which the drugs are being obtained/used must be followed.

Use of remote injection systems

  • In some countries a firearms licence may be required for use of remote injection equipment.
    • e.g. in the UK, anyone possessing a blow-pipe, dart-gun etc. which can be used to discharge tranquillising drugs (i.e. for remote injection), must be authorised by a Firearms Certificate. This is issued by the police. (B284.5.w5)
Author Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Suzanne I. Boardman BVMS MRCVS (V.w6)
References B284.5.w5, B345.6.w6, B486.11.w11, D315.3.w3, J1.33.w16, J1.33.w17, J2.30.w5, P1.1997.w9, P504.2001.w5, V.w6

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