Statistical Issues in Bioavailability/Bioequivalence Studies

For the approval of generic drug products, bioavailability/bioequivalence studies are often conducted to demonstrate that the drug absorption profiles in terms of the extent and rate of absorption of test products are bioequivalent to those of the innovative drug product. The bioavailability/bioequivalence studies are often conducted under a standard two-sequence, two-period (2x2) crossover design. Under the standard 2x2 crossover design, statistical methods are well established for the assessment of bioequivalence. However, it is a concern whether approved generic drug products can be used safely and interchangeably. In this article, drug interchangeability under a replicated crossover bioavailability/bioequivalence study is discussed. Several controversial statistical issues that are commonly encountered in the assessment of bioequivalence are discussed. In addition, some frequently asked questions during regulatory submissions are reviewed. Recommendations regarding possible resolutions are made whenever possible. Some concluding remarks on the feasibility of the application of current methods for bioequivalence to the assessment of biosimilarity of follow-on biologics are also presented.