In order to discuss TDM and PGx we need to also introduce the concept of pharmacokinetics.
Pharmacokinetics is the study of drug disposition in the body: It concerns how and when drugs enter the circulation, how long they remain in the blood, and how they are ultimately eliminated from the body.
TDM is the clinical assessment of a drug's pharmacokinetic properties. Physicians and pharmacists often need to establish that a drug is present at a clinically-effective concentration yet does not reach a toxic concentration.
The next few pages will describe some of the factors that determine a drug's disposition in the body. These factors ultimately decide the need for therapeutic drug monitoring.