Test code links throughout this Guide refer to the corresponding test in the User's Guide. Toxicology Clinical Pharmacokinetics and Therapeutic Drug Monitoring by Michael Bottorff, Pharm. D. Pharmacokinetics is defined as the change of drug absorption, distribution, metabolism, and excretion over time. Clinical pharmacokinetics applies these principles of drug disposition to patient care by correlating changes in serum drug concentrations to observed therapeutic and toxic effects.
Several reasons exist for clinically monitoring drugs with the aid of pharmacokinetics.
In most cases there is a better clinical relationship between serum concentration and patient response than exists for drug dose and patient response. In addition, higher serum concentrations carry an increased risk for toxicity. Finally, a drug is suited for monitoring with serum concentration determinations when the presence of disease states or abnormal conditions or the presence of other drugs dramatically alter the levels achieved with a given dose. To better understand the contribution of a drug's pharmacokinetics to TDM, the concepts of drug absorption, distribution, metabolism, and excretion should be reviewed. Absorption For drugs not administered intravascularly, an absorption process occurs that can delay the attainment of blood concentrations adequate for a drug response.