ABSTRACT

For a drug product under development, it is of interest to study how the drug moves through the body and the processes of movement such as absorption (A), distribution (D), metabolism (M), and excretion (E) after drug administration. This leads to the study of pharmacokinetics (PK). The key concept of a PK study is to study what the body does to the drug, which is usually characterized by ADME of a drug product after administration. In practice, however, we cannot measure concentrations at the site of action directly. Instead, we can measure concentrations in blood, plasma, or serum that reflect ADME at the site of action. The site of action is defined as the site at which the drug will have its effect. Concentrations have valuable information regarding ADME that allows manipulation of concentrations in early drug development so that the concentrations will remain within the therapeutic window (or index) of safety and efficacy. The bioequivalence testing described in Chapter 10 is to show that the primary PK parameters such as AUC and Cmax, which reflect the extent and rate of drug absorption of the test product are not too high to avoid toxicity (safety) on one hand and are not too low to produce response (efficacy) on the other hand as compared to those of the reference product (innovative or brand name drug product).