Demonstrating the bioequivalence of a generic drug product means showing that it can deliver the same amount of the same drug to the site(s) of therapeutic action at the same rate and to the same extent as the brand name product. For many systemically acting drug products, evaluating bioequivalence involves administering the product (e.g., a tablet taken by mouth) and then drawing blood at scheduled times to measure the amount of the drug in the circulation at each point.
A plot illustrating how the resulting drug concentration in the blood increases and decreases over time is called a pharmacokinetic profile. If the brand name and generic drug products exhibit the same profiles, then the rate and extent to which the drug becomes available at the relevant site(s) of action are the same, and the safety and efficacy of the generic drug product will be the same as that of the brand name drug product. Alternatively, if the pharmacokinetic profiles do not match (as depicted in Figure 1), then the drug products cannot be considered equally safe and efficacious.
This pharmacokinetic approach is one of the most accurate, sensitive, and reproducible ways to evaluate bioequivalence. It is also relatively efficient and has been used to establish bioequivalence and support the approval of most systemically acting generic drug products.