Xylazine-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 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)


Suggested doses:

  • Ursus arctos - Brown bear
    • Xylazine 2.4-2.8 mg/kg plus tiletamine-zolazepam 3.6-4.2 mg/kg. (J345.14.w6)
  • Ursus maritimus - Polar bear:
    • Xylazine 2 mg/kg plus tiletamine-zolazepam 3 mg/kg (total drugs 5 mg/kg): 4.8 mg/kg total drugs in captive-held and 5.5 mg/kg total drugs in free-ranging wild polar bears. (J1.39.w5)

During induction:

During anaesthesia:

  • Good muscle relaxation throughout immobilisation in Ursus maritimus - Polar bear and Ursus arctos - Brown bear. (J1.39.w5, J345.14.w6)
  • Expect heart rates of about 50-70 beats per minute. (D156.w2)
  • Ursus maritimus - Polar bear
    • Rectal temperature increased over time during the immobilisation (whereas in bears immobilised with tiletamine-zolazepam it decreased over time). Compared with Tiletamine-Zolazepam Anaesthesia in Bears, bears showed lower heart rate, higher mean arterial pressure, lower SpO2, lower arterial oxygen tension (PaO2) and lower blood pH. (J1.39.w5)
    • Better analgesia than with Tiletamine-Zolazepam Anaesthesia in Bears, based on responses of pulse rate and mean arterial pressure to the stimulus of haemostats clamping a claw bed: significant changes in both pulse rate and arterial pressure with tiletamine-zolazepam, but non-significant changes with xylazine-tiletamine-zolazepam. (J1.39.w5)
  • Ursus arctos - Brown bear: pulse rate about 50-70 bpm, respiratory rate about 20 breaths per minute reducing during one hour of anaesthesia to about 10 breaths per minute. Low SpO2 (<85%) and/or blue-tinged mucous membranes in some bears indicating transient hypoxaemia during initial anaesthesia. This can be treated by providing supplemental oxygen. (J345.14.w6)
  • In Ursus maritimus - Polar bear, with tolazoline, 3.8 +/- 0.9 mg/kg half given intravenously, half given intramuscularly, reversal took 33.9 +/- 1.6 minutes (range 22.5-70.5 minutes). With atipamezole (0.15 mg/kg) or yohimbine (0.2 mg/kg), all bears were still recumbent 15 minutes after injection. (J1.39.w5)
  • In Ursus arctos - Brown bear, yohimbine was given at the mean dose rate of 0.19 mg/kg, either intramuscularly or half intramuscularly, half intravenously. Note: Giving half intravenously, half intramuscularly appeared to give faster recovery. (J345.14.w6)
  • [Editor's note: Atipamezole, rather than yohimbine, is now normally used for reversing alpha-2 agonist drugs.]

During recovery:

  • In Ursus maritimus - Polar bear, with tolazoline, 3.8 +/- 0.9 mg/kg half given intravenously, half given intramuscularly, reversal took 33.9 +/- 1.6 minutes (range 22.5-70.5 minutes). With atipamezole (0.15 mg/kg) or yohimbine (0.2 mg/kg), all bears were still recumbent 15 minutes after injection. (J1.39.w5)
  • In Ursus arctos - Brown bear, following injection with yohimbine, pulse, respiratory rate and reflexes increased within a short time (minutes) but recovery time (to standing) was not consistent: mean +/- SD 19.7 +/- 2.9 minutes, median 15.0 minutes, range2.0-64.0 minutes. (J345.14.w6)
Appropriate Use (?)
  • Reduced volume of drugs is required compared with Tiletamine-Zolazepam alone (J1.39.w5, J345.14.w6) e.g. in a study in wild Ursus arctos - Brown bear, about 3.9 mL per bear versus 8.5 mL per bear for tiletamine-zolazepam. (J345.14.w6)
  • Small total volume allows use of air or gas pressurised darts rather than darts with internal explosive charges, which may reduce muscle damage at the point of injection. (J1.39.w5, J345.14.w6)
  • Rapid physiological responses to administration of the alpha-2 antagonist yohimbine allow effective treatment of adverse responses (bradycardia, hypoxaemia, hyperthermia) which may occur during anaesthesia. (J345.14.w6)
  • Useful for immobilisation with better analgesia than with tiletamine-zolazepam alone. (J1.39.w5)
Complications/ Limitations / Risk
  • Mixing at a 2:3 Xylazine:Tiletamine-Zolazepam ratio by adding 1.1 mL 300 mg/mL xylazine and 1 mL sterile water to one vial containing 500 mg lyophilized tileatamine-zolazepam, to give a total volume of 2.5 mL (the lyophilised powder contributes abut 0.4 mL, approaches the threshol between solution and suspension, and it is difficult to keep the drugs in suspension at low temperatures (<10 C). 
    • A slightly lower concentration, 300 mg/mL mixed drugs can be achieved by adding 1.1 mL of 300 mg/mL xylazine and 1.3 mL sterile water to one vial containing 500 mg lyophilized tileatamine-zolazepam, to give a total volume of 2.8 mL. This remains in solution at lower temperatures and the volume required for bear immobilisation is about 50% of that required using tiletamine-zolazepam alone. (J1.39.w5, J345.14.w6)
    • A 2:3 mixture can be produced by adding 3.3 mL of 100 mg/mL xylazine to a 500 mg vial of lyophilized tiletamine-zolazepam, giving a final volume of 3.7 mL per vial (the lyophilized powder contributes about 0.4 mL). (J1.39.w5)
  • Possibility of hyperthermia in Ursus arctos - Brown bear at high (> 25 C) ambient temperatures. (J345.14.w6)
  • Transient hypoxaemia may occur (mucous membranes blue-tinged, or measured by pulse oximetry) and should be treated with supplemental oxygen. (J345.14.w6)
  • Physical injury, sometimes severe or even fatal, can occur when bears are darted. (P9.2004.w4, J40.32.w1, D249.w10)
Equipment / Chemicals required and Suppliers
  • Xylazine

  • Tiletamine-Zolazepam

  • Needles, syringes

  • Darting equipment

  • Supplemental oxygen: "D" size aluminium oxygen cylinder with mini-regulator and nasal cannula recommended in the field. Available from ambulance supply companies. (J345.14.w6)

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.
  • Tiletamine-Zolazepam is not licensed for use in all countries. (J59.19.w1)
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 wildlife 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.
    • For example, in the UK, anyone possessing a blow-pipe, dart-gun etc. which can be used to discharge tranquillising drugs (i.e., can be used 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, B486.11.w11, D249.w10, J1.39.w5,  J40.32.w1, J59.19.w1, J345.14.w6, P9.2004.w4, V.w6

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