A bioequivalence study is a type of clinical trial designed to compare the biological equivalence of two different formulations of a drug. Such studies are typically conducted in controlled clinical settings with human subjects, who are randomly assigned to receive two formulations. The two formulations are then compared with respect to their pharmacokinetic profiles, which encompass the absorption, distribution, metabolism, and elimination of the drug. Under the guidance from Food and Drug Administration (FDA), for a size-$\alpha$ bioequivalence test, the standard approach is to construct a $100(1-2\alpha)\%$ confidence interval and verify if the confidence interval falls with the critical region. In this work, we clarify that $100(1-2\alpha)\%$ confidence interval approach for bioequivalence testing yields a size-$\alpha$ test only when the two one-sided tests in TOST are ``equal-tailed''. Furthermore, a $100(1-\alpha)\%$ confidence interval approach is also discussed in the bioequivalence study.

翻译：生物等效性研究是一种临床试验，旨在比较药物两种不同制剂的生物学等效性。此类研究通常在受控的临床环境中进行，受试者被随机分配接受两种制剂。随后，通过比较两种制剂的药代动力学特征（包括药物的吸收、分布、代谢和消除）来评估其差异。根据美国食品药品监督管理局（FDA）的指导，对于大小为$\alpha$的生物等效性检验，标准方法是构建一个$100(1-2\alpha)\%$置信区间，并验证该置信区间是否落在临界区域内。本研究阐明，仅当TOST中的两个单侧检验为“等尾”时，采用$100(1-2\alpha)\%$置信区间进行生物等效性检验才能得到大小为$\alpha$的检验。此外，本文还讨论了生物等效性研究中$100(1-\alpha)\%$置信区间的方法。