Merck Manual

Please confirm that you are a health care professional


Factors Affecting the Activity of Poisons


Barry R. Blakley

, DVM, PhD, Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan

Last full review/revision Jul 2011 | Content last modified Nov 2016

The consequences of poisoning depend on many factors in addition to the actual toxicity of the poison itself. The dose is a primary concern, but the exact amount of poison an animal has been exposed to is seldom known. The length of time and the number of times the animal is exposed are important. The way in which the animal is exposed affects how much of the poison is absorbed, how it spreads through the body, and perhaps how it is metabolized. The time of intake of the poison can also be a factor. For example, if the stomach is empty when an animal eats a poisonous substance, vomiting may occur. If the stomach is partly filled, the poison may be retained and lead to toxic effects. Environmental factors, such as temperature and humidity, affect rates of consumption and even whether or not some toxic agents are present. For example, many plant poisons are associated with seasonal or climatic changes, such as winter cold and rainfall.

Different species can react differently to a particular poison because of variations in absorption, metabolism, or elimination. For example, species unable to vomit, such as horses or rabbits, can be poisoned with a lower dose. The age, size, nutritional status, stress level, and overall health of an animal are important factors. In young animals, metabolism is compromised by underdeveloped systems.

The chemical nature of a poison determines its ability to dissolve. Poisons that dissolve in water spread more easily than those that do not. Substances added to the active ingredient, such as binding agents, outer coatings, and sustained-release preparations, also influence absorption. Generally, as absorption is delayed, toxicity decreases.

Droplet size is an important consideration in sprays and dips, because the dose increases when the droplets are larger. This is one of many reasons to closely follow label instructions and recommended applications. Only formulations intended for animals should be used.

Others also read

Also of Interest