Veterinary toxicology involves the evaluation of toxicoses, identification and characterization of toxic substances, determination of their fate in the body, and treatment of toxicoses. Recognizing the vital role that veterinary toxicology plays in animal health is imperative for ensuring proper recognition and treatment of exposures to toxins.
A knowledge of toxicology is important for veterinarians who treat production animals because it enables them to keep the animals safe and the world's food supply secure. Veterinary toxicology plays a vital role in animal health and food safety by focusing on potentially fatal exposures to toxic agents in an animal's environment that affect all species of animals, from companion pets to food-producing animals whose end product is intended for human consumption.
Veterinary toxicology can be clinically challenging because of the low frequency of cases observed in an individual clinical practice setting and the wide variation in exposure histories. Animal poison control centers such as Pet Poison Helpline are available to assist animal owners and veterinarians in cases of potential exposures to toxic agents for all species.
In many cases of toxicosis in companion animals, the specific substance, timing, and amount that the patient was exposed to are unknown. In food-producing animals, toxic exposures often involve a large number of animals and thus have the potential for appreciable economic loss. When malicious intent or negligence results in poisoning, litigation can be involved.
Toxicological Terminology
Toxic substances may be variably referred to as poisons, toxicants, toxins, or venoms.
The term poison refers to a noninfectious substance that, when produced in or introduced to the body by means of a process such as ingestion, inhalation, dermal contact, or injection, especially in small doses, causes pathophysiological effects by chemically (rather than physically) interfering with normal biological processes.
The term toxicant is often used interchangeably with "poison." Although it is commonly defined as any poisonous agent, whether natural or artificial, the term "toxicant" is sometimes preferred when referring to a toxic substance that is either the main product or a by-product of human activity (eg, pesticide manufactured for commercial use, dioxin produced as a by-product of an industrial process).
The term toxin (eg, botulinum toxin, Amanita toxin, tetrodotoxin, phytotoxins) is often used to refer to a toxic substance produced by a biological source (ie, a biotoxin) or identical compounds reproduced via genetic engineering (recombinant toxins). However, it is also commonly used synonymously with "poison."
The term venom (eg, snake venom, spider venom, bee venom, platypus venom) is used especially for toxins secreted by animals and delivered through a venom delivery apparatus (a bite or sting). Venomous animals are generally distinguished from animals that are poisonous to eat or touch (those with passive delivery of poison).
Toxicosis, poisoning, and intoxication are synonymous terms for the disease produced by a toxic agent. Acute toxicosis refers to effects during the first 24 hours after exposure. Effects produced by prolonged exposure (≥ 3 months) are referred to as chronic toxicosis. Terms such as "subacute" and "subchronic" cover the large gap between acute and chronic. Toxidrome (toxic syndrome) refers to a group of clinical signs associated with a given toxic exposure.
Toxicity refers to the quality of being poisonous or to the extent of virulence of a poison. The term "toxicity" is commonly used synonymously with "poisoning" or "toxicosis," even though this usage is considered technically incorrect.
All toxic effects are dose dependent. The amount of a toxic agent necessary to produce a detrimental effect is often characterized by various toxicity ratings (eg, toxicity threshold, toxic dose).
The toxic dose is the threshold quantity of a compound above which harmful effects occur after a single exposure. Toxic doses can be expressed as the quantity of a compound per body weight of the affected animal (eg, the toxic dose of acetaminophen for a cat is 50–100 mg/kg).
The median lethal dose (LD) is the dose that is lethal to 50% of the subjects in a test sample. It is an estimator of lethality and the most common expression used to rate the potency of toxic agents.
When toxicity can result above a certain threshold of a compound in feedstuffs, water, or air, the toxic threshold concentration can be expressed as parts per million (ppm) or parts per billion (ppb). If agents are known to result in toxicity when they are present in concentrations above a certain threshold in animal tissues, the thresholds measured in affected tissues can also be expressed in ppm or ppb concentrations. For solid materials, ppm and ppb are equivalent to units of mcg/g and mcg/kg, respectively. For fluids, ppm and ppb are equivalent to units of mcg/mL and mcg/L, respectively. For atmospheric concentrations, ppm and ppb can also be expressed in units of mg/m3 and mcg/m3, respectively, through a conversion factor based on molecular weight and atmospheric temperature and pressure.
Other terms used for prediction of disease or lethality include "no observed effect level" (NOEL), "maximum nontoxic dose" (MNTD), and "maximum tolerated dose" or "minimum toxic dose."
For More Information
Peterson ME, Talcott PA, eds. Small Animal Toxicology. 3rd ed. Elsevier; 2013.
Gupta RC, ed. Veterinary Toxicology: Basic and Clinical Principles. 3rd ed. Elsevier; 2018.
Klaassen CD (ed.), Casarett LJ, Doull J. Casarett and Doull's Toxicology: The Basic Science of Poisons. 9th ed. McGraw-Hill; 2019.
Also see pet health content regarding poisoning.
