Bioequivalence means that different preparations of a drug are given the same dose under the same experimental conditions, and there is no obvious difference in absorption speed and degree. When the difference of absorption speed is not significant in clinic, some pharmaceutical preparations can be considered as bioequivalent under the condition of the same absorption degree but different speeds. Bioequivalence is different from drug equivalence. Drug equivalence means that the same drug is made into the same dosage form, but the inactive ingredients are not necessarily the same, and the content, purity, uniformity, disintegration time limit and dissolution rate meet the same prescribed standards. Drug equivalence can not reflect the situation of drug preparation in vivo. The study of bioequivalence parameters is a very complicated system engineering. At present, many researchers are exploring more suitable parameters to evaluate bioequivalence. In the process of bioequivalence evaluation, it is generally believed that auc is not only suitable for single-dose and multi-dose research, but also suitable for immediate-release preparations and controlled-release preparations. However, there are many controversies about the selection of pharmacokinetic parameters reflecting the absorption rate. Cmax and tmax are still used as assessment indicators to reflect the absorption rate in the guidelines of drug supervision departments in most countries.
American basson believes that cmax measures the final absorption of drugs, while tmax can reflect the absorption rate of drugs. Therefore, he proposed to determine tmax at equal time intervals in the expected absorption stage, which constituted a counting process, providing a theoretical basis for comparing the absorption rates of two or more prescriptions. At the same time, he also suggested that the role of cmax should be limited to the investigation of "burst effect" to evaluate the safety of drugs.
Considering the complexity of in vivo processes of different drugs and the absorption and metabolism characteristics of sustained and controlled release preparations, Professor Yu Fengchi and Master Wei Wu think that other pharmacokinetic parameters of tmax, such as half-life (t 1/2) and minimum retention time (mrt), should also be considered when evaluating the bioequivalence of drugs.