Chemical Immobilization Pharmacology: Other Anesthetic Drugs
The San Diego Zoo Wildlife Alliance (SDZWA) is among the zoological societies, universities and other organizations in the US that offer education in safe capture chemical immobilization techniques for those who are interested in pursuing careers in veterinary medicine, wildlife biology or wildlife management. SDZWA’s series of courses on safe capture chemical immobilization techniques contains pharmacology segments on neuromuscular blocking drugs, opioids, tranquilizers and cyclohexamines.
The final pharmacology module in the SDZWA series is Chemical Immobilization Pharmacology: Other Anesthetic Drugs. This describes other drugs that are used in the immobilization and anesthesia of wildlife. A description of this course is available on the organization’s website.
Choosing Drugs for Chemical Immobilization
There are numerous published sources available for veterinarians seeking the best anesthetics to use for immobilizing wildlife. Typically however, veterinarians who are experienced in this area will have sufficient knowledge of the drugs and drug classes that perform optimally for the various species of wildlife they encounter. For those who are not well-versed in this practice, it is prudent to consult with a veterinarian who routinely immobilizes the target species of interest to find out what drug combinations are preferred for the species and specific situation.1,2
It is important to realize that when selecting drugs for immobilization, there is no one ideal drug that works for all wildlife. Today, the most effective drugs for the immobilization of wildlife are drug combinations, usually of differing drug classes.
A drug or drug combination should have a high therapeutic index in order to ensure a safe, effective induction. With today’s formulated drug combinations, it is actually safer to slightly overdose an animal than it is to slightly underdose. The reason for this is that modern formulations are far safer than in years past, and are unlikely to bring about morbidity, whereas, underdosing can lead to the injury of an animal as it attempts to escape (e.g., following the remote delivery of drugs). Underdosing can also increase an animal’s susceptibility to hyperthermia, trauma and capture myopathy.1
When remotely delivering anesthetics, drug potency is critical. The goal should be to immobilize the animal with one dart. Most of the drug combinations available today can fit into a 2-, 3-, or 4-ml dart. More concentrated anesthetics also result in less tissue trauma due to decreased volume injected. Thus, they are absorbed faster and result in a quicker induction.2
Another important consideration in drug selection is a drug’s ability to be antagonized. Depending on the target animal and the conditions at hand, rapid recovery at the desired time is a significant advantage when immobilizing wildlife.
Benzodiazepines
Benzodiazepines are a class of drugs that include diazepam, midazolam, and zolazepam. These drugs decrease anxiety while producing calming effects and profound skeletal muscle relaxation. Benzodiazepines are metabolized in the liver and excreted in the urine and feces.3 They produce minimal sedation because most animals remain alert and aware of their surroundings. Benzodiazepines can cause excitement in healthy animals; thus, they are not commonly used as sole agents. Benzodiazepines are more effective when combined with cyclohexamines, tranquilizers, or opioids.
Alpha‐2 Agonists (also α-2 Agonists)
Alpha‐2 agonists are used for their sedative and analgesic properties in a variety of species. When used as the sole agent, they do not produce an adequate level of anesthesia for even minor surgical procedures. Commonly-used α-2 agonists include medetomidine (Domitor®), dexmedetomidine (Dexdomitor®) and xylazine (Rompun®). Xylazine is the most commonly-used α-2 agonist in traditional small animal practices.
Alpha‐2 agonists are often used in combination with ketamine, making them much more useful and effective as anesthetics for surgical procedures.2
Some advantages of using α-2 agonists include their producing short duration analgesia and that they can be combined with ketamine to produce adequate surgical anesthesia in many species. They can also be reversed with a α-2 antagonists such as atipamezole. Disadvantages can include cardiovascular depression (decreased heart rate, cardiac output, and hypotension), transient hyperglycemia following administration and vomiting in cats.
Propofol
Propofol is a unique anesthetic agent. It is an oil/water emulsion, and is administered via IV only. Propofol is metabolized quickly, has a fast induction, and has a short duration of effect. Redosing is safe via multiple low-dose injections given for short procedures.
Propofol’s potential side effects include a transient decrease in cardiac contractility and hypotension due to vasodilation. Propofol is a potent respiratory depressant; if given too rapidly, it can cause apnea following induction. This can be greatly diminished by slow injection, titrating to effect, and the use of premedications that lower the dose of propofol required.4
Interested in learning more about safe capture? The San Diego Zoo now offers courses in safe capture techniques and best practices. Learn reliable, safe, and effective techniques for the species you work with and the scenarios you encounter!
2Arnemo, J., Kreeger, T. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed. Sunquest Publishing, 2007, 432 pages.
3Plumb’s Veterinary Drugs.
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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