Bioequivalence and bioavailability

Bioequivalence is defined as the interchangeability of two pharmaceutical specialties that have the same active principle ingredient (API) and equivalent bioavailability. This definition leads us to bioavailability, which refers to the amount of drug that actively reaches the circulation and the speed at which it accesses it, that is, the fraction of drug capable of reaching the site of action. It depends on the physicochemical characteristics of the active principle ingredient, the excipients, the manufacturing process and the preservation of the pharmaceutical form, and also on the intrinsic characteristics of the individual, such as intestinal motility or gastric pH.

Any modification in any of these factors can alter both the total amount of active principle ingredient absorbed and the rate at which it is absorbed. For this reason, in the development of a generic pharmaceutical specialty, despite the fact that it is the same active principle ingredient, the same dose and the same pharmaceutical form, these factors can determine a different bioavailability than that of the reference product.

Consequently, two pharmaceutical specialties have an equivalent bioavailability if both the concentration of the active drug and the rate at which it accesses the systemic circulation are within an interval considered equivalent, when they are administered at the same doses and under the same experimental conditions.