Carfentanil citrate
for reversible immobilization of large hoof stock. It is generally delivered via dart although oral administration has been successful in black bear [Ramsay et al. 1995, J Wildl Dis. 31(3): 391-393] and chimpanzee [Kearns et al. 1996, Proc AAZV p. 401-403].
General Information and History
Carfentanil citrate was the first opiate to be developed for use in wild and exotic species following the introduction of etorpine (M-99) in the early 1960s. Carfentanil was
developed in the mid 1970s by Janssen Pharmaceuticals of Beerse, Belgium directed by Dr. Paul Janssen. It was a product of expanding the fentanyl series of opiate agonists for
human use including alfentanil and sufentanil. The high potency of carfentanil did not lend itself to routine human applications, but Dr. Janssen and his team quickly recognized its potential in wildlife capture and anesthesia.
Wildlife Pharmaceuticals began research on the safety and efficacy of carfentanil in
North American species, completing the FDA registration process in 1989. Commercial production of carfentanil citrate under the trade name Wildnil ceased in 2003. It is now available as a compounded pharmacy product by prescription only.
Use in Wildlife Management
Carfentanil citrate has become the drug of choice for chemical capture of large North American hoof stock such as free-ranging moose, elk, bighorn sheep and bison. It has particular application in animals that are chased by vehicle or helicopter as endogenous catecholamines will not block the pharmaceutical action of this potent opiate agonist. It has been used orally in bears with limited success. Its use and effectiveness in exotic equids (zebra, onager, etc) and feral horses is limited and variable.
Use in Domestic Species
Carfentanil has no routine uses in the common domestic species.
Pharmacology and Chemistry
Carfentanil citrate has a morphine-like analgesic mode of action and produces rapid immobilization following intramuscular injection. Carfentanil is an analogue of the opioid fentanyl with a quantitative potency approximately 100 times that of fentanyl and 10,000 times that of morphine.
Carfentanil citrate is methyl 4- (1-oxopropyl) phenylamino-1- (2 phenylethyl) -4-piperidine carboxylate-2 hydroxy-1, 2, 3-propanetricarboxylate (1:1).
CONTRAINDICATIONS AND PRECAUTIONS
Veterinarians and biologists using carfentanil should be familiar with clinical procedures such as measurement of pulse and respiration, prevention of aspiration, relief of bloat, control of shock and hemorrhage, recognition of hyperventilation and heat exhaustion, the immobilization of fractures, etc. In cases of severe excitement during induction or delayed recovery, continued observation is necessary to correct any of the above and to insure the animal does not injure itself.
Adequate ventilation - especially in cages or crates - is mandatory; keep head and neck in position to insure patent air passage and to prevent aspiration of stomach contents.
In animals that are recumbent for a considerable length of time, care should be taken to avoid eye damage; shading to prevent retinal burning is advisable and a bland ophthalmic ointment is beneficial. Predatory birds such as magpies have been known to peck at the eyes of recumbent animals. Following carfentanil administration, a brief period of visual adjustment occurs and it may be necessary to direct animals away from hazards such as water, ravines, trees, etc.
Care should be taken not to dart animals in the abdomen (intraperitoneally) or against bone. The ideal locations are the heavy muscles of the shoulder or rump. Use a heavy initial dose and avoid subsequent fractional doses. Injection into fat depots results in slow absorption; use needles of adequate length to insure deep intramuscular injection.
As with any anesthetic or immobilization procedure in wild or exotic species, extreme care must be exercised when the drug is used during high environmental temperatures or following extended pursuit or any other activity that may result in elevated body temperatures. Supplies and equipment to shade the animal and control hyperthermia should be available when using carfentanil during periods of hot weather. High ambient temperatures increase risk when using carfentanil. Spraying and/or shading animals are useful to lower body temperature. Never use carfentanil when the temperature is in the 100 degrees F range. Also, high humidity and/or extreme altitude cause stress.
Lateral recumbency is hazardous in all ruminants. One must be prepared to employ proper procedures to handle problems resulting from lateral or sternal recumbency. Lateral recumbency may call for immediate position correction and injection of the antidote Naltrexone HCl. Animals in or near water may require immediate assistance to prevent drowning or aspiration. Prolonged periods of lateral recumbency in heavy animals have caused radial paralysis. Adequate padding may be helpful and Naltrexone should be administered as soon as feasible. Animals that exhibit hyperexcitability, anxiety and hyperventilation should either be given one additional dose of Carfentanil citrate to quiet them to prevent excessive hyperventilation and alkalosis or administered Naltrexone HCl as an antidote.
The transportation of animals given carfentanil requires careful surveillance to prevent excessive struggling, injury or death. Do not transport more than one animal in a sling, stall or crate.
WARNING:
Carfentanil citrate must never be used unless an adequate amount of the reversal agent (Naltrexone hydrochloride) is immediately available
Do not use Carfentanil citrate in animals that display clinical signs of severe cardiovascular or respiratory disease or impairment. Avoid use during breeding season.
ADVERSE REACTION
Seven drug related fatalities were reported during clinical trials that involved the immobilization of 509 members of the family Cervidae (deer, elk, moose). Mortalities were attributed to hyperthermia, acute myopathy and/or narcotic recycling in 3.8% (6/158) of moose and less than 1% (1/295) of elk immobilized in clinical trials.
HUMAN WARNING
Other reported adverse reactions included tachycardia, tachypnea, excitement during induction, respiratory depression, erratic breathing, thrashing, torticollis, excessive salivation, regurgitation of rumen contents and delayed renarcotization.
Carfentanil citrate is an extremely potent drug and is to be used ONLY by individuals experienced in handling potent rapid immobilizing agents in zoos, exotic animal and wildlife practices, wildlife management procedures and biological research.
Carfentanil citrate must be treated with extreme respect and caution. Since carfentanil may be employed in locations distant from emergency medical facilities, users must ALWAYS observe the following PRECAUTIONS:
- User should SEEK PROFESSIONAL MEDICAL ATTENTION IMMEDIATELY if the drug is accidentally ingested or injected.
- At least two people in the field team should be able to RECOGNIZE SIGNS OF TOXICITY and have FIRST AID KITS containing resuscitation aids available.
- WORK IN PAIRS when loading syringes or darts with carfentanil. Wear rubber
gloves when loading syringes to avoid accidental spills on hands. - DO NOT SPRAY, squirt or spill the drug when filling syringes.
- WASH AT ONCE with large volumes of water if carfentanil comes in contact with
skin or mucous membranes. - PRACTICE GOOD CLINICAL TECHNIQUE. Do not hold used needles in
mouth. Always insure that darts and syringes contain proper dose. - All reasonable efforts should be made to LOCATE and RETRIEVE any loaded
DARTS that missed the target animal. - RESPECT all dart guns, darts and delivery syringes as though they were loaded.
INFORMATION FOR PHYSICIANS
Carfentanil citrate is a powerful synthetic opiate. Accidental human exposure may produce severe central nervous system depression resulting in respiratory depression or failure followed by coma. Depending on route of administration, effect may be noted in 2 to 30 minutes. Treatment should start immediately by administering appropriate opiate antagonist, providing airway support, plus cardiopulmonary resuscitation techniques.
RECOMMENDED DOSE RANGE FOR CERVIDAE
| SPECIES | DOSE (MG/KG) |
| Moose (Alces americana) | .006 - .014 |
| Elk (Cervus elaphus) | .005 - .020 |
| Axis Deer (Axis axis) | .005 - .010 |
| Sitka Deer (Odocoileus hemionus sitkensis) | .005 - .011 |
For members of the family Cervidae, a dose range of .005 - .020 mg/kg has been found to be safe and effective. Immobilization is usually achieved 2 to 10 minutes following administration. The lower end of the dose range is suggested for those animals of quiet temperament, under confinement, that have not been pursued prior to administration of the drug, or in poor physical condition. The upper dose range is suggested for animals of excitable temperament following extensive pursuit or in instances where an extremely short time to effect is desirable. Some exotic species of deer (Eld’s, Pampas, Muntjac, and Indian hog deer) may require a higher dose for immobilization. The highest dose required for immobilization in clinical trials was 0.064mg/kg in Muntjac deer.
The most effective dose rate will vary due to condition of use. The upper end of the dose range may also be appropriate for animals being pursued by vehicle or aircraft when an extremely quick knockdown time is desired or when individuals are known to be highly excitable. In all instances, all factors including nutritional, reproductive and health status of an animal, as well as environmental conditions (temperature, cover and terrain) must be evaluated by the user and best professional judgment used.
ADMINISTRATION
Inject dose deep into a large muscle mass of the neck, shoulder, back or hindquarter. Intrathoracic, intra-abdominal or subcutaneous injection is to be avoided. To ensure proper dosage for animals weighing less than 50 kg, remove required calculated dose of carfentanil with a tuberculin syringe. Dilute to appropriate volume with sterile water for injection prior to administration.
FDA Approved Presentation for Carfentanil citrate
Carfentanil was approved by the FDA in a 3mg/ml concentration.
Compounded Forms Possible
Carfentanil is commonly compounded at a concentration of 3mg/ml in a 10ml vial.
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