Etorphine Anaesthesia in Bears  (Disease Investigation & Management - Treatment and Care)

Summary Information
Type of technique Health & Management / Disease Investigation & Management / Techniques:
Synonyms and Keywords M99 anesthesia in bears

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
  • Note. This drug is no longer recommended for use; better drugs are available. (B407.w18)
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:

  • 10-60 g/kg (micrograms per kilogram) has been used; this can be placed into a single dart for remote injection, and is reversible. (B10.48.w43)
  • Etorphine hydrochloride, 0.5-1.5 mg has been used with bears weighing 55-350 kg, causing immobilisation in all cases but varying depths of narcosis. (B16.9.w9)
  • Etorphine (in combination with acepromazine in Immobilon LA), at 0.8-1.5 mg etorphine per 100 kg body weight (use the lower dose rage for larger bears). (B407.w18)
  • In Ursus maritimus - Polar bear:
    • 2 mg for yearlings,3 mg for two-year-old cubs, 5-7 mg for most females and smaller adult bears, 7-14 mg for large males. (P84.1.w1)
    • 0.035 mg/kg. (B345.6.w6)
  • In Ursus americanus - American black bear:
    • 0.02 mg/kg. (B345.6.w6)
    • 0.016 mg/kg; for large bears, an estimated 0.018-0.020 mg/kg is suggested, to avoid underdosing. (J345.3.w5)
    • 1.0 mg total for black bears of approximately 300 lb (136 kg). (J1.5.w5)
  • In: Ursus arctos - Brown bear: 0.02 mg/kg(B345.6.w6)
    • In wild grizzly bears Ursus arctos - Brown bear, doses given varied widely: (J1.16.w15)
      • In cubs, 0.073-0.132 mg/kg. (J1.16.w15)
      • In yearlings, 0.031-0.101 mg/kg. (J1.16.w15)
      • In adults, 0.011-0.036 mg/kg. (J1.16.w15)
  • In female captive bears, Ursus arctos - Brown bear, Tremarctos ornatus - Spectacled bear and Melursus ursinus - Sloth bear, Large Animal Immobilon at 1.3 +/- 0.2 mg per 100 kg bodyweight etorphone plus 6.9 +/- 0.4 mg per 100 kg acepromazine, plus 300 iu hyaluronidase. (J370.51.w1)

During induction:

  • Minimise disturbance during induction; brief convulsions have been reported in response to loud noises late in induction. (P84.1.w1)
  • The bear slows down, stumbles and shows disorientation before developing recumbency. (P84.1.w1)
  • Eyes close, head is lowered and sways. (J4.175.w2)
  • With a dosage of 0.033 +/- 0.014 mg/kg in Ursus maritimus - Polar bear, immobilization occurred in 7.2 +/- 4.4 minutes. (P84.1.w1)
  • With a dosage of 0.0034 mg/kg in Ursus maritimus - Polar bear, induction time was mean 11 minutes. (P84.1.w1 - see Larsen, 1971)
  • "Rapid" induction; noted to be "within ten minutes" for four or five Ursus americanus - American black bear which had been given 0.020 mg/kg or higher. (J345.3.w5)
  • In wild grizzly bears Ursus arctos - Brown bear
    • In cubs, given 0.073-0.132 mg/kg, induction in 3.0-4.0 minutes. 
    • In yearlings, given 0.031-0.101 mg/kg, induction in 1-10 minutes .
    • In adults, given 0.011-0.036 mg/kg, induction in 3.0-11.0 minutes.


  • Bears which collapse in less than 15 minutes usually are safe to approach; those taking longer should be approached with caution even after they are recumbent. (P84.1.w1)
  • A positive palpebral reflex indicates the bear is not fully anaesthetised and requires more time to reach full immobilisation or requires further anaesthetic. (P84.1.w1)

During anaesthesia:

  • Careful monitoring is required; the bear's respiratory rate may drop as low as two breaths per minute. (B407.w18)
  • Greatly reduced respiratory rate. (J345.3.w5)
    • Respiratory rate may be as low as 2-4 breaths per minute. (P84.1.w1)
  • In wild grizzly bears Ursus arctos - Brown bear, respiratory rates were 2-4 breaths per minute, heart rates 32-64 bpm. (J1.16.w15)
  • Overdosing is common and causes respiratory depression which can be fatal. (B407.w18)
  • In the event of severe respiratory depression or apnoea, give artificial respiration. (P84.1.w1)

Duration of anaesthesia:

Reversal with antagonist:

  • Diprenorphine hydrochoride ((M50-50) is the usual antagonist for etorphine (M99). (P84.1.w1)
    • Diprenorphine at 2 mg diprenorphine per 1 mg etorphine given. Administer intravenously or intramuscularly. (B345.6.w6)
  • LA Immobilon can be reversed using diprenorphine (Revivon): give a volume of Revivon equal to the volume of Immobilon LA used. (B407.w18)
  • Etorphine can be reversed using diprenorphine (M50-50) or nalorphine hydrobromide, giving increased respiratory rates and respiratory movement depth, but sometimes recumbency has persisted for 12 to 24 or even 48 hours. (B16.9.w9)
  • Etorphine can be reversed using naloxone hydrochloride, 25 mg naloxone per 0.5 mg etorphine given. (J4.175.w2)

During recovery:

  • Reversal is rapid following intravenous injection of antagonist. (P84.1.w1)
    • Rapid recovery of Ursus americanus - American black bear following injection of the reversal agent. (J345.3.w5)
      • Intravenous injection resulted in recovery in mean 5.5 minutes (range les than one minute to 19 minutes). (P84.1.w1)
    • In polar bears, intramuscular injection of antagonist gave recovery in mean 31 minutes (range 20-45 minutes). Intravenous injection gave recovery sometimes in as little as 1-3 minutes. (P84.1.w1)
  • Rapid reversal following injection of naloxone hydrochloride, e.g. 2-4 minutes. Initially development of several deep breaths, then the eyes opened, then the bear lifted its head, stood and walked off. (J4.175.w2)
    • Sometimes only partial recovery, with initial walking followed by return to sternal recumbency and lack of response to auditory or physical stimuli for a prolonged period (overnight). (J4.175.w2)
  • In wild grizzly bears Ursus arctos - Brown bear, recovery after 4.0-5.0 minutes in bears given diprenorphine intravenously and intramuscularly, and 7.0-10.0 minutes in bears given diprenorphine intramuscularly only. (J1.16.w15)
Appropriate Use (?)
  • No longer recommended for use; better, safer drugs are available. (B407.w18)
  • Rapid induction. (J345.3.w5)
  • Careful monitoring of respiration is important. (B407.w18)
Complications/ Limitations / Risk
  • Etorphine is lethal to humans in very small quantities. (P84.1.w1)
    • Darts should be made up in advance, not e.g. in a helicopter. (P84.1.w1)
  • Underdosed individuals may show excitement. (J345.3.w5)
  • Respiratory depression can be severe. (B345.6.w6, B407.w18)
  • Respiratory rate may be as low as 2-4 breaths per minute; with overdosing, respiratory depression or apnoea may occur. (P84.1.w1)
  • Overdosing is common and causes respiratory depression which can be fatal. (B407.w18)
  • Bears anaesthetised with etorphine may show a very low heart rate. (J345.3.w5, P84.1.w1)
  • Peripheral vasodilatation may result in depressed body temperature. (J345.3.w5, P84.1.w1)
  • Muscle relaxation is not good. (J4.175.w2)
  • Physical injury, sometimes severe or even fatal, can occur when bears are darted. (P9.2004.w4, J40.32.w1, D249.w10)
  • Recovery following injection of the reversal agent tends to be slower than in ungulates. (B407.w18)
  • Avoid loud/sudden noises. There are reports of bears partially waking during etorphine anaesthesia. (D315.3.w3)
Equipment / Chemicals required and Suppliers
  • Darting equipment

  • Etorphine (M99) or LA Immobilon

  • Reversal agent - usually diprenorphine hydrochloride (M50-50, Revivon).

  • Antagonist for human use - naloxone (Narcan)

Expertise level / Ease of Use
  • Bears are large, powerful carnivores. Anaesthesia of bears should be carried out by experienced personnel. (V.w6)
  • Etorphine must be used only be experienced personnel. 
  • Etorphine should never be used when working alone. The specific antagonist for humans (naloxone) must always be available and someone must be present who (a) can give the antagonist in the case of accidental human injection and (b) can give artificial respiration if necessary in the case of accidental human injection.
Cost/ Availability
  • Controlled drug. (B407.w18, P84.1.w1)
Legal and Ethical Considerations
  • This is a controlled drug. (B407.w18, P84.1.w1)
  • Etorphine (M99) is highly toxic to humans. Always consider whether it is necessary to use this drug, or whether alternatives are available.
  • Etorphine should never be used when working alone. The specific antagonist for humans (naloxone) must always be available and someone must be present who (a) can give the antagonist in the case of accidental human injection and (b) can give artificial respiration if necessary in the case of accidental human injection.
  • If this drug is to be used then telephone numbers for one or more local hospitals must be readily available.
  • Dirty needles and syringes must be disposed of properly (needles always into a properly marked sharps container. (D249.w10)

Use of Drugs (Medication):

  • Etorphine is generally a controlled drug (regulations may vary between countries).
    • 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).).
  • 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).

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)

Human safety considerations

  • There is an inherent risk of human injury when using potent animal capture drugs. It is important to use protocols which prevent such accidents. Additionally, protocols should be established to deal with what may be a potentially lethal exposure. (P1.2006.w3)
  • Accidental exposure to capture drugs should always be considered an emergency which needs a calm, prompt, organised response. (P1.2006.w3)
  • In the event of human exposure to an animal capture drug, the aim of treatment is to maintain life until professional medical care is available. (B70.A1.w3)
  • Particularly when carrying out immobilsations in remote locations, the capture team must be self-reliant for dealing with situations, possibly life-threatening, including cardio-respiratory arrest, respiratory depression, CNS depression and hypotension. "As a minimum when working in the field the following precautions should be adhered to: use capture drugs only with a second, trained person present; respect the potency of the drugs and do not take chances by underestimating a potentially dangerous situation; never work with opioid drugs without having the human antidote and administration protocol in the emergency kit; and limit personnel present when working with the drugs." (P1.2006.w3)
    • Both a thorough theoretical understanding and practical experience in cardiopulmonary resuscitation are essential. (P1.2006.w3)
    • Several members of the capture/immobilisation team should be trained in cardiopulmonary resuscitation. (P1.2006.w3)
  • Note that the laws regarding administration of medical treatment to accident victims by personel who may not be officially qualified vary between countries. (B70.A1.w3, P1.2006.w3)
Author Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Suzanne I. Boardman BVMS MRCVS (V.w6)
References B10.48.w43, B16.9.w9, B284.5.w5, B345.6.w6, B407.w18, B486.11.w11, D315.3.w3, J4.175.w2, J345.3.w5, P84.1.w1, V.w6

Return to Top of Page