Chemical Immobilization Pharmacology: Tranquilizers

Chemical Immobilization Pharmacology: Tranquilizers is one among many courses offered by the San Diego Zoo Wildlife Alliance (SDZWA) in safe capture chemical immobilization techniques. Such courses are typically taken by those who are interested in or who are pursuing careers in veterinary medicine, wildlife biology or wildlife management. A description of this course is available on the SDZWA website.

Oftentimes, the terms “tranquilizer” and “sedative” are used interchangeably, but tranquilizers typically reduce anxiety and induce a sense of tranquility without drowsiness, while sedatives have a more profound effect and produces significant drowsiness.¹ Many drugs used as tranquilizers, sedatives and analgesics cannot be categorized by only one pharmacologic effect, and some across these categories may have additional effects.

Classes of Tranquilizers

Tranquilizers are commonly used in veterinary medicine to produce calmness, as chemical immobilants, and as an adjunct to general anesthesia. These drugs often have different mechanisms of actions, pharmacodynamic effects, analgesic properties, reversibility, and physiological effects.²

The drug classes most often used as tranquilizers in veterinary medicine include:

Phenothiazine Derivatives—These were originally developed as antipsychotic drugs for the treatment of schizophrenia in humans, but have been used in veterinary medicine as tranquilizers since the 1950s. Examples of phenothiazines include acepromazine, promazine and chlorpromazine.

Butyrophenone Derivatives—Butyrophenones were also introduced into human medicine in the 1950s as antipsychotics. This class of drugs is less commonly used in veterinary medicine; examples include azaperone, haloperidol and droperidol.

Benzodiazepine Derivatives—Benzodiazepines were first discovered in 1954.¹ They are considered sedative-hypnotics due to their propensity to cause anxiolysis, sedation, and an ability to cause sleep.² Benzodiazepines are often classified as minor tranquilizers. Examples of benzodiazepines include diazepam, midazolam, lorazepam, and zolazepam.

Alpha-2-Adrenergic Receptor Agonists—These drugs are very popular in veterinary medicine because they produce profound, reliable sedation as well as analgesia.² The first α2-adrenergic agonist drug used in veterinary medicine was xylazine.¹ Alpha-2-adrenergic receptor agonists act synergistically with opioids and their effects can be reversed with the use of α2-adrenergic antagonist drugs. Besides xylazine, other examples include detomidine, medetomidine, dexmedetomidine, levomedetomidine and clonidine.

Tranquilizing medications for veterinary use are typically available through both industry-leading wildlife pharmaceuticals companies and custom veterinary compounding pharmacies. Like other veterinary prescription drugs, they are restricted by US federal law to use by or on the order of a licensed veterinarian.

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!