Toxins and Poisons - Overview

Poison

Any substance when applied to the body outwardly or in any way introduced to it, in sufficient quantity, can interfere with the life processes of cells by its own inherent qualities

Toxin Classifications

• effects on body

  • corrosives

  • protoplasmic and parenchymatous poisons

  • nerve poisons

  • poisons affecting blood

• chemical or physical nature

  • inorganic

  • organic

• source of compound

  • exogenous

  • exogenous

Factors affecting poisonings

• dose: “in sufficient quantity”

• route of administration

• chemical and physical properties

• source of toxin

• species differences

• age, sex, metabolic size

• general state of health

Dose

• dose is related to duration of exposure

  • dose response curve

• Lethal Dose 50 (LD50)

  • dose at which 50% of treated animals die from exposure (not done anymore due to animal welfare concerns)

  • metric for comparison of poisons

Poison route of administration

• route of administration may alter effects

  • some compounds are toxic when absorbed one way, but not toxic when administered another way

• inhalation → poison can cover large surface area in the lungs

• absorption from GI tract

  • type of Gi tract influences metabolism and absorption

  • poison may be modified by stomach acid or enzymes

  • rumen may dilute or alter metabolism (protective or enhanced)

• intact skin

• injection (IV, IM, SQ)

Chemical and physical properties of poisons

• physical factor: particle size

  • affects efficiency of absorption

• chemical form

  • affects action of substance, absorption, and excretion

  • solubility in fluids

  • compatibility with transport mechanisms

Source of toxin

• may affect both dose and chemical or physical nature

• plant poisons may occur in differing concentration in various parts

  • stems

  • leaves

  • seeds/fruits

  • roots

• source may be related to chemical nature of compound

Species differences relating to poisonings

• thickness of the integument

• metabolic and physiological differences

• digestive tract length and absorption → affects rate of passage

Diagnosis of poisonings

• history of exposure may or may not be present

• signs are rarely pathognomonic

• clinical signs may increase index of suspicion

• large number of types of compounds can be poisonous thus complicating analytical techniques

• diagnosis is dependent on demonstration of poison in tissues “in sufficient quantity”

  • just because the toxin is present does not mean there is enough of it to cause disease