How are Animals Tranquilized?

In veterinary medicine, sedatives and tranquilizers are commonly used in animals to produce calmness, for chemical restraint, and as an adjunct to general anesthesia.¹ In general, tranquilization reduces anxiety and induces a sense of tranquility without drowsiness, while sedation has a stronger effect and produces drowsiness and hypnosis. That said, there can be some overlap in the drug classes and types that are used to produce both tranquilization and sedation. Drugs that produce tranquilization and sedation have different mechanisms of actions, physiological effects, pharmacodynamics, levels of analgesia and reversibility.²

Veterinary Tranquilizers and Sedatives

Phenothiazines

Phenothiazines (or neuroleptics) were originally developed and used as antipsychotic drugs for the treatment of schizophrenia in humans, but these have been used in veterinary medicine as tranquilizers for over 50 years.¹Acepromazine is the most widely used phenothiazine derivative in veterinary medicine. While it is only FDA-approved for use in dogs, cats, and horses in the U.S., it is routinely used off-label for sedation of many veterinary species.

Benzodiazepines

Benzodiazepines are classified as sedative/hypnotics due to their ability to cause light sedation and sleep.¹ They are used in veterinary medicine as anticonvulsants, adjuncts to anesthetic induction agents, muscle relaxants and for behavioral modification. In healthy animals, behavioral effects are mild. Diazepam, midazolam, lorazepam and zolazepam are examples of benzodiazepines.

Alpha-2-Adrenergic Receptor Agonists (α-2 Adrenergic Agonists)

Alpha-2-adrenergic agonist drugs are very widely used in veterinary medicine due to their ability to produce significant, reliable sedation as well as analgesia. These drugs also act synergistically with opioids. Alpha-2-adrenergic agonists can be reversed with the use of α2-adrenergic antagonists.² Xylazine is the most widely used α-2 adrenergic agonist in veterinary medicine. Other drugs in this class include detomidine, romifidine, medetomidine and dexmedetomidine.

Routes of Administration

Depending upon the class of drug used, venue and requirements, the administration of tranquilizing and/or sedative drugs may be oral, intravenous or intramuscular.² In the traditional veterinary clinic treating domestic species, this is generally a straightforward proposition. While hand injection is the most direct method of tranquilizing/sedative agents to an animal, this becomes a necessity in the case of many unrestrained nondomestic species. For exotic species, injectable agents are usually used; in the zoo setting, this may be accomplished via a pole syringe. For potentially dangerous animals and those in the field, remote delivery systems consisting of a dart and projector are the most practical options.

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!