Chemicals / Complex Chemical Agents/ Chemical:
Etorphine (with special reference to Bears)




Information in this page has been entered to support the current volumes of Wildpro and further information will be added as new volumes are completed. This page is not intended to substitute for the manufacturer's data sheet and the information is not yet complete for all species, or for all contra-indications etc.

CAUTION: Before any pharmaceutical product is used, the manufacturer's data sheet, containing information on uses, dosage and administration, contra-indications, warnings etc., should always be consulted. It is important to remember that licensing of pharmaceutical products for use in a particular species/condition, as well as mandatory meat and milk withdrawal times for food-producing animals, varies between countries and changes with time. Withdrawal times also may vary between different pharmaceutical formulations and depending on route of administration. In Europe the prescription cascade must be followed. In the USA, FARAD may be consulted regarding residues and meat and milk withdrawal times.

General Chemical Information


A potent semi-synthetic opiate used for immobilisation, particularly of large ungulates.

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Names and Formulae

Type Semi-synthetic opioid derived from thebaine. (B70.A1.w2)
Alternative Names
  • Etorphine hydrochloride (B70.A1.w2)
  • 6,14-endoetheno-7alpha-(2-hydroxy-2-pentyl)-tetrahydro-oripavine hydrochloride (B70.A1.w2)
  • M99 (B70.A1.w2)
  • Immobilon (etorphine/phenothiazine tranquillizer mixtures) (B121)
    • Immobilon L.A. (Etorphine 2.45 mg/mL plus Acepromazine 10 mg/mL) (B121)
    • Immobilon S.A. (Etorphine 0.074 mg/mL plus methotrimeprazine 18 mg/mL) (B121)
Chemical Formula --
Chemical Structure --
Molecular Weight --
Related Chemicals Morphine. Etorphine is 500-10,000 times as potent as morphine.

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Physical Properties / Chemistry

  • Powder. (B70.A1.w2)

  • Solutions are clear and colourless. (B70.A1.w2)

Melting point --
Boiling point --
Density --
Water solubility Readily soluble in slightly acidified water. (B70.A1.w2)
Other solubility In DMSO (dimethyl suphoxide), solutions up to 10 mg/mL may be made. (B70.A1.w2)
Acid/Base --

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Pharmacology & General Information

Pharmacology --
Storage / Stability
  • Store solutions in a cool place (below 25 C) away from light. (B70.A1.w2)
  • Keep in the container supplied. (B70.A1.w2)
Legal Category (In UK) --

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Associated Techniques




(Further Reading)
Click image for full contents list of ELECTRONIC LIBRARY

Authors Debra Bourne (V.w5)
Referees Suzanne I. Boardman (V.w6)

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Therapeutic Information


  • Used alone, etorphine produces areflexia without total loss of consciousness. (B70.A1.w2)
  • Changes in gait or walking pattern occur; some (more nervous) animals may run for extended periods. Ruminants can often be approached and guide while still on their feet. (B70.A1.w2)
  • Immobilisation progresses and the animal either suddenly collapses to recumbency (sternal or lateral), or stops, sways and then becomes recumbent. (B70.A1.w2)
  • Onset of action is usually 2-4 minutes, sometime sup to eight minutes, with peak action usually following in 15-30 minutes and lasting about one hour. (B70.A1.w2)
Appropriate Use
  • For immobilisation and capture of African ungulates, particularly very large ungulates and subungulates. (B70.A1.w2)
  • Not suitable for use in most carnivores. (B70.A1.w2)
  • Not recommended for domestic cats or wild Felidae. (B121)
  • Produces CNS stimulation prior to depression, resulting in a period of excitement. (B121)
  • Spontaneous recovery is slow. (B70.A1.w2)
  • Recovery is delayed by enteroheptic recycling. (B121)
  • Can be successfully reversed with diprenorphine, nalorphine or naloxone. (B70.A1.w2)
  • Reverse with 3-5 times the dose of etorphine in elephants, rhinoceros and giraffes, and with 2-3 times the dose of etorphine in other species. (B70.A1.w2)
  • Note: naloxone is rapid-acting but has a short half-life; higher doses are required to prevent renarcotization: give 0.04-0.07 mg/kg subcutaneously followed by 0.1-0.25 mg/kg intravenously or occasionally intramuscularly. (B70.A1.w2)
  • Large Animal Revivon contains 3.0 mg/mL diprenorphine. Given as the same volume as the volume of Immobilon L.A. used for immobilization. (B121)

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Pharmacokinetics and Drug Interactions
Absorption /Bioavailability --
Distribution --
Plasma Protein binding / Storage --
Elimination Route --
Elimination half-life / Clearance Rate --
Drug Interactions --

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Formulations available --
Doses / Administration Routes / Frequencies In ungulates
  • Ranging from 0.5 g/kg in rhinoceros to 5 g/kg in camels. (B70.A1.w2)
  • Lower doses are generally needed for young, old, sick and debilitated individuals. (B70.A1.w2)
  • Females generally require a slightly lower dose than males of the same species. (B70.A1.w2)
  • Pregnant animals appear to be more resistant than non-pregnant individuals. (B70.A1.w2)
  • Note: Tamer animals generally need much lower doses than do free-living animals. (B70.A1.w2)
  • Etorphine may be combined with a sedative (e.g. Xylazine (Sedative analgesic) (Chemical Page)), a tranquilliser (e.g. acetylpromazine or azaperone) or an antimuscarinic agent (e.g. hyoscine) to reduce knock-down time and some of the adverse reactions which may be seen when etorphine is used alone. (B70.A1.w2)

In bears (see Etorphine Anaesthesia in Bears for further details):

  • 10-60 g/kg 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)
  • In Ursus americanus - American black bear, 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 wild grizzly bears Ursus arctos - Brown bear, doses given varied widely: (J1.16.w15)
    • In cubs, 0.073-0.132 mg/kg. 
    • In yearlings, 0.031-0.101 mg/kg .
    • In adults, 0.011-0.036 mg/kg.


Monitoring parameters
  • Monitor respiration, cardiovascular output and for regurgitation. (B70.A1.w2)

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Withdrawal period / Withholding time

Notes --

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Toxic Information

Toxic effects of Pharmaceutical Products

Contraindications / Precautions --
Adverse Effects / Side Effects / Warnings
  • Respiratory depression, rumen stasis and decreased GIT mobility, heart rate and blood pressure changes, decreased urine output, excitement. (B70.A1.w2)
    • Excitement can be overcome by use of sedatives or tranquillisers. (B70.A1.w2)
    • Depression of respiratory rate and minute volume may lead to severe hypoxia, hypercapnoea and progressive acidosis. (B70.A1.w2)
    • Cardiovascular alterations have proved fatal in equids. (B70.A1.w2)
    • In many domestic ungulates, hypertension has been reported; also in rhinoceros, and this is presumed also in many non-domestic ungulates, based on cardiovascular responses. (B70.A1.w2)
    • Passive regurgitation of rumen contents is not uncommon. (B70.A1.w2)
      • This may lead to fatal aspiration. (B70.A1.w2)
  • In horses:
    • Intense muscular activity; the recumbent animal is very stiff, with violent muscle tremors, particularly for the first 20 minutes. (B121)
    • Very high heart rate and blood pressure but severely depressed respiration. (B121)
    • Occasionally become violently excited soon after reversal to standing. (B121)
    • Excitement may recur several hours later, probably due to enterohepatic recycling of the etorphine. (B121)
Operator Warnings
  • Humans are particularly sensitive to etorphine. (B70.A1.w2)
    • Effects are evident within two minutes of injection and peak in 5-10 minutes. (B70.A1.w2)
    • Signs include loss of consciousness, slow, shallow respiration, cyanosis, pin-point pupils, weak pulse, fall in blood pressure, muscle twitching and death due to respiratory failure. (B70.A1.w2)
    • Administer 1 mL naloxone (0.4 mg/mL, Narcan) intramuscularly or preferably intravenously, immediately and repeat at intervals of 2-3 minutes until symptoms are reversed. (B70.A1.w2)
Overdose / Acute Toxicity
  • Particularly respiratory depression. (B70.A1.w2)
    • Treat with an appropriate antagonist and if necessary with an analeptic such as doxapram. (B70.A1.w2)

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Detailed Toxicological Information

Classification --
Acute Toxicity --
Chronic Toxicity --
Reproductive effects --
Teratogenic effects --
Mutagenic effects --
Carcinogenic effects


Organ toxicity --
Bird Toxicity --
Aquatic organism activity --
Other organism toxicity --

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Nutrient Information

Nutritional Data

Sources --
Biological Use --
Recommended Daily Allowance / Recommended level in food --
Stability in food (Storage time) --
Interactions --

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External / Environmental Information

External / Environmental Uses

Use --
Formulation --
Application method --
Application Concentration --
Persistence of Effect / Frequency of Application --

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Sources in the Environment

Natural sources --
Human-associated sources


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Effects on the Environment

Effects in the aquatic environment


Effects on land --

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Persistence in the Environment

Breakdown in soil and groundwater


Breakdown in water --
Breakdown in vegetation --

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