Sedation for Wild Animals
Historically, the pharmacological immobilization of wild animals can be traced back to certain South American tribes who used curare-coated arrows to take down prey animals. Curare is an alkoloidal neurotoxin and muscle relaxant that competes with acetylcholine, thereby blocking transmission of information transmitted between cells. Thus, curare derivatives were initially used in attempts to formulate standardized sedation agents for wildlife.
In the late 1950s however, rangers in South Africa sought to develop “new and hopefully more efficacious methods to immobilize animals for research.”1 In subsequent years, great strides have been made in developing new drugs and techniques for delivery in wildlife species.
Classes of Sedation Agents
Many different classes of compounds have been used to immobilize animals. These include anesthetics, analgesics, sedatives and tranquilizers. Today, however, only a limited number of these can be used, due to federal regulations. One of these, the U.S. Food and Drug Administration’s Controlled Substances Act of 1970, restricts the use and distribution of some of the more potent drugs such as opioids.2
Opioids, as a class of drugs, has three advantages:
1) They are easy to administer (due to the high potency of the members used, less than 1ml can immobilize most animals),
2) they have a high therapeutic index, and
3) the high availability of antagonists to reverse their effects.2
Opioids have good analgesic but only limited muscle relaxant properties. They have a wide margin of safety, are predictable in action, and can be reversed with the administration of a suitable antagonist (diprenorphine, naloxone or nalorphine). Neuroleptic synergists can potentate the opioid and produce a smoother induction.3
The side effects of opioid immobilization include excitation following administration, resulting in aimless running, pacing, or walking, which may lead to hyperthermia or capture myopathy, regurgitation; critical depression of respiration; muscular tremors, hyper-or hypotension; tachycardia; and recycling. Opioids are extremely toxic and must be handled with the greatest care to avoid accidental exposure in humans.
Cyclohexamines are rapid-acting, dissociative anesthetics. Used in many species, they are known to be particularly effective in carnivores, bears, primates, birds, and reptiles. Side effects of cyclohexamines include muscle rigidity, excessive salivation, hyper- or hypotension, vocalization, or convulsions.
The cyclohexamines are fast acting, have a wide margin of safety, cause only moderate depression of respiration and circulation at optimum doses, and have a quick recovery because of rapid metabolism of the drug. They are often used in combination with neuroleptics and there are no known antagonists.2
Ketamine hydrochloride is a cyclohexamine that has been used successfully for years in many species.3 Combinations of cyclohexanone dissociative anesthetic agents combined with benzodiazepines, which offer smooth induction and good muscle relaxant qualities can be obtained through custom compounding pharmacies.
Alpha2-Adrenergic Agonists are potent central nervous system depressants with sedative, muscle relaxant, and some analgesic properties. They may be used singly for immobilization, or as synergists with opioids or cyclohexamines. Their effect is dose dependent and ranges from mild sedation to deep sleep.
At high doses, alpha2-adrenergic agonists may cause critical depression of respiration and blood circulation. In very excited animals, they do not produce a satisfactory level of immobilization. They may also disrupt the thermoregulatory mechanisms, leading to hyper- or hypothermia. Recovery from high dosages is usually prolonged and difficult. The development of specific antagonists has increased the usefulness of the alpha2-adrenergic agonists for animal immobilization.
Alpha2-agonists presently available include xylazine, detomidine and medetomidine. An example of a widely used immobilization drug combination is the 5/1 combination of ketamine and xylazine. Ketamine, as the primary drug, causes a rapid onset of drug action; the inclusion of xylazine results in a smoother induction and counteracts the adverse side effects of ketamine.3
Neuroleptics produce a calming or tranquilizing effect with minimal analgesia. They do not produce immobilization and are primarily used as synergists with opioids or cyclohexamines. In that capacity they have proven effective in potentiating the immobilizing drug, decreasing the total dose, causing a smoother and more speedy induction, and negating undesirable side effects. The drugs in this group include the phenothiazine derivatives, the butyrophenones, and the benzodiazepines.3
Long-Acting Neuroleptics (LANs) facilitate adaptation to a new environment or transportation is a relatively new concept. They are typically employed during activities such as capture, confinement, transportation, or integration into a new herd or group, because these are traumatic events. Some species are particularly susceptible to stress, which may lead to high anxiety levels, refusal of food and water, self-injury, injury from other animals (rank fights), and exhaustion with fatal consequences.3
1Carl, J., Schwarzer, M., Klingelhoefer, D., Ohlendorf, D., & Groneberg, D. A. (2014). Curare - a curative poison: a scientometric analysis. PloS one, 9(11), e112026.
2Williams, D. E. and Riedesel, D. H. (1987). Chemical Immobilization of Wild Ruminants, Iowa State University Veterinarian: Vol. 49 :Iss. 1, Article 6.
3Wenker, C. Anesthesia of Exotic Animals. The Internet Journal of Anesthesiology. 1997 Volume 2, Number 3.
About NexGen Pharmaceuticals
NexGen Pharmaceuticals is an industry-leading veterinary compounding pharmacy, offering sterile and non-sterile compounding services nationwide. Unlike other veterinary compounding pharmacies, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.
Our pharmacists are also encouraged to develop strong working relationships with our veterinarians in order to better care for veterinary patients. Such relationships foster an ever-increasing knowledge base upon which pharmacists and veterinarians can draw, making both significantly more effective in their professional roles.
Disclaimer
The information contained in this blog post is general in nature and is intended for use as an informational aid. It does not cover all possible uses, actions, precautions, side effects, or interactions of the medications shown, nor is the information intended as medical advice or diagnosis for individual health problems or for making an evaluation as to the risks and benefits of using a particular medication. You should consult your veterinarian about diagnosis and treatment of any health problems. Information and statements have not been evaluated by the Food and Drug Administration ("FDA"), nor has the FDA approved the medications to diagnose, cure or prevent disease. Medications compounded by NexGen Pharmaceuticals are prepared at the direction of a veterinarian. NexGen Pharmaceuticals compounded veterinary preparations are not intended for use in food and food-producing animals.
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