Variability and impact on design of bioequivalence studies

Area of Science:

• Pharmacokinetics and Drug Metabolism
• Regulatory Science
• Pharmaceutical Sciences

Background:

• European regulatory bodies are updating bioequivalence (BE) guidance for immediate-release systemic drugs.
• Revisions address scientific discussions on statistical methods and study designs for drugs with high within-subject variability.
• Previous guidance, established a decade ago, requires updates due to evolving scientific understanding.

Purpose of the Study:

• To review and discuss the evolving regulatory guidance for bioequivalence investigations.
• To explore statistical analysis methods and study designs for drugs with high within-subject variability.
• To examine the causes of variability in drug concentration-time profiles.

Main Methods:

• Review of European Medicines Agency (EMA) draft guidance (2008).
• Analysis of scientific literature on bioequivalence study designs and statistical methods.
• Examination of Food and Drug Administration (FDA) bioequivalence study data (2003-2005).

Main Results:

• New approaches allow wider bioequivalence limits (e.g., 75-133%) based on within-subject variability.
• Partial replicate designs and reference-scaled average bioequivalence are proposed for high-variability drugs.
• Extensive pre-systemic metabolism identified as a key cause of high variability, more so than formulation.

Conclusions:

• The updated European guidance reflects advancements in statistical analysis and study design for bioequivalence.
• Understanding variability mechanisms, like pre-systemic metabolism, is crucial for accurate bioequivalence assessment.
• These scientific efforts are influencing regulatory guidance revisions globally.