Bioavailability (BY) is the rate and degree of absorption of the active substance through the pharmaceutical form and reaching its site of action in the body. The main parameters used to measure the bioavailability of an orally administered drug are “area under the plasma concentration-time curve (Area Under the Curve, AUC)” and “plasma peak maximum) drug concentration (Cmax).
Bioequivalence (BE) is that two different drug products that are pharmaceutical equivalent (for example, both tablets / capsules) have similar bioavailability and hence therapeutic effects after administration at the same molar doses.
According to national and international up-to-date guidelines, the comparison of the bioavailability of two different drug products (test / generic / equivalent product and reference / innovator / original product) in the same healthy volunteers is made over the test / reference ratios of Cmax and AUC in BE studies. While the first of these two parameters reflects the degree and speed of bioavailability, the second reflects the degree of bioavailability. Cmax is also important for reliability as it also indicates the maximum amount of drug the body is exposed to. Cmax and AUC are the “primary variables (parameters)” that form the benchmark for BE studies.
Bioequivalence studies are carried out in a limited number of healthy / volunteer people and under special experimental conditions, and the BY of the produced as equivalent to the KI of the original drug is compared and it is desired to be equivalent to each other in certain proportions. For this purpose, subjects are given one of the drugs first, and the other after a washout period - usually - only in a single dose. Plasma levels of the drugs are measured, mostly during 24-48 hours and at certain intervals by taking blood.