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Factors Affecting the Activity of Poisons |  |
| Poisoning potential is usually determined more by the multitude of related factors than by the actual toxicity of the poison. Exposure-related, biologic, or chemical factors regulate absorption, metabolism, and elimination, and thus, influence the clinical consequences (if any). |
| Factors Related to Exposure: |
| The dose is a primary concern; however, the exact intake of poison is seldom known. Duration and frequency of exposure are important. The route of exposure affects absorption, translocation, and perhaps metabolic pathways. The time of administration relative to periods of stress, food intake, etc, may also be a factor, eg, following ingestion of some toxicants, emesis may occur if the stomach is empty, but if partly filled, the toxicant is retained and poisoning can occur.
Environmental factors, such as temperature, humidity, and barometric pressure, affect rates of consumption and even the occurrence of some toxic agents. Many mycotoxins and poisonous plants are correlated with seasonal or climatic changes, eg, the ischemic effects of ergot poisoning are more often observed during the winter cold, and plant nitrate levels are affected by rainfall amounts. |
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| Biologic Factors: |
| Various species and strains within species react differently to a particular poison because of variations in absorption, metabolism, or elimination. Functional differences in species may also affect the likelihood of poisoning (eg, species unable to vomit can be intoxicated with a lower dose of some agents). |
| The age and size of the animal are primary factors in poisoning. Metabolism and translocation of xenobiotic agents are compromised by the underdeveloped microsomal enzyme system in young animals; membrane permeability and hepatic and renal clearance capabilities vary with age, species, and health. Generally, the amount of toxicant required to cause poisoning is correlated to body weight, but with greater body weight, a disproportionate increase in toxicity (per unit body
weight) of a compound often occurs. Body surface area may correlate more closely with the toxic dose; no measurement parameter is consistent for every situation. |
| Nutritional and dietary factors, hormonal and health status, organ pathology, stress, and sex all affect poisoning. Nutritional factors may directly affect the toxin (ie, by altering absorption) or indirectly affect the metabolic processes or availability of receptor sites. (The copper-molybdenum-sulfate interaction is an example of both.) |
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| Chemical Factors: |
| The chemical nature of a toxicant determines solubility, which in turn influences absorption. Nonpolar or lipid-soluble substances tend to be more readily absorbed than polar or ionized substances. The vehicle or carrier of the toxic compound also affects its availability for absorption. Isomers, including optical isomers, vary in toxicity (eg, the γ isomer of hexachlorocyclohexane [Lindane] is more toxic than other isomers). |
| Adjuvants are formulation factors used to alter the toxicologic effect of the active ingredient (eg, piperonyl butoxide enhances the insecticidal activity of pyrethrins). Binding agents, enteric coating, and sustained-release preparations influence absorption of the active ingredient. Generally, as absorption is delayed, toxicity decreases. Flavoring agents affect palatability, and thus the amount ingested. |
| Droplet size is an important consideration in sprays and dips because the dose increases with larger droplet size. This is one of many reasons to adhere closely to label instructions and recommended applications. Only formulations intended for animals should be used. |
| Contaminants and impurities may affect poisoning or be the primary toxicant (eg, dioxins,
Halogenated Aromatic Poisoning: Introduction). |
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