LEARNING OBJECTIVE: Identify how poisons are introduced into the body and the factors that affect their toxicity.

Toxicology is the science of poisons, their actions, their detection, and the treatment of the conditions produced by them. A poison is a substance that, when inhaled, swallowed, absorbed, applied to the skin, or injected into the body in relatively small amounts, may cause damage to structures or disturbances of function. Poisons act by changing the normal metabolism of cells or by actually destroying them.

The effects of poisons may be local or remote, and in some instances, poisons can produce both effects. A local effect is produced when a poison only affects the area in which it is applied. A remote effect is produced when a poison affects parts of the body that are remote to the site of application or point of introduction. Poisons sometimes show no effect—or only a slight effect—until several doses have been taken. Then, suddenly, an effect is produced that nearly equals that produced by taking the whole amount at onetime. This is known as a cumulative effect.

The toxicity of poisons depends upon their method of introduction into the body and how fast they are absorbed by the body. For example, snake venom taken into the mouth or into the stomach during first aid treatment of snakebite is not ordinarily harmful, but snake venom injected parenterally is extremely poisonous.

Various conditions affect an individual’s reaction and susceptibility to poisons. For instance, some individuals by nature are unusually sensitive to certain poisons (such as venom from bee stings), while others possess a natural tolerance. Additionally, the age of the victim can affect the severity of the poisoning. Young children, for example, are normally more susceptible to poisons than adults. Habitual use of certain poisons, such as narcotics, may cause individuals to become accustomed to a poison’s effects, even though the amount taken by these individuals would ordinarily be considered lethal. This habitual use of poisons, however, may result in a sudden hypersensitivity that could be deadly. The actions of poisons may also be considerably modified by disease, some diseases increasing and others lessening the action of poisons.

Poisons are eliminated from the body by way of the kidneys, liver, gastrointestinal tract, and skin. Poisons are eliminated either unchanged or in the form of other compounds. These compounds are the result of chemical changes made in various body organs and tissues.