Poisoning and Drug Overdosage

Poisoning refers to the development of dose-related adverse effects following exposure to chemicals, drugs, or other xenobiotics. To paraphrase Paracelsus, the dose makes the poison. In excessive amounts, substances that are usually innocuous, such as oxygen and water, can cause poisoning. Conversely, in small doses, substances commonly regarded as poisons, such as arsenic and cyanide, can be consumed without ill effect. There is, however, substantial individual variability in the response to, and disposition of, a given dose. Some of this variability is genetic, and some is acquired on the basis of enzyme induction or inhibition, or because of tolerance. Poisoning may be local (e.g., skin, eyes, or lungs) or systemic depending on the chemical and physical properties of the poison, its mechanism of action, and the route of exposure. The severity and reversibility of poisoning also depend on the functional reserve of the individual or target organ, which is influenced by age and preexisting disease.