Pharmacokinetic and Toxicokinetic Principles

Pharmacokinetics is the study of the absorption, distribution, metabolism, and excretion of drugs. Mathematical models and equations are used to describe and to predict this behavior. Pharmacodynamics is the term used to describe an investigation of the relationship of drug concentration to clinical effect. Toxicokinetics, which is analogous to pharmacokinetics, is the study of the absorption, distribution, metabolism, and excretion of a xenobiotic under circumstances that produce toxicity or excessive exposure. Toxicodynamics, which is analogous to pharmacodynamics, is the study of the relationship of toxic concentrations of xenobiotics to clinical effect. Xenobiotics are all substances that are foreign to the body.

Despite confounding and individual variability, toxicokinetic principles can be applied to overdose situations to facilitate our understanding and to make certain predictions. These principles can be used to help evaluate whether a certain antidote or extracorporeal removal method is appropriate for use, when the serum concentration might be expected to drop into the therapeutic range (if such a range exists), what ingested dose might be considered potentially toxic, what the onset and duration of toxicity might be, and what the importance of a serum concentration is. While considering all these factors, the clinical status of the patient is paramount, and mathematical formulas and equations can never substitute for evaluating the patient.

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