Study Design as the Determinant of Bioequivalence Outcomes: Implications for Regulatory Science and Access to Medicines in Africa

Abstract

Bioequivalence (BE) studies are fundamental to the approval of generic medicines, serving as surrogates for clinical efficacy by demonstrating comparable pharmacokinetic exposure to reference products. While regulatory frameworks emphasize endpoints such as area under the curve (AUC) and maximum concentration (Cmax), the role of study design in determining BE outcomes remains underappreciated. This editorial argues that study design, not merely formulation quality, is the primary determinant of BE success or failure. In Africa, where regulatory systems are increasingly requiring robust BE data, inadequate study design represents a critical barrier to timely access to affordable medicines. We examine key determinants of BE study design, including variability, statistical power, dissolution methodologies, and comparator selection, and highlight the urgent need to strengthen capacity in advanced regulatory science across the continent.

Introduction

The global expansion of generic medicines has been predicated on the use of bioequivalence (BE) studies as a scientifically valid and ethically efficient alternative to large-scale clinical trials. Regulatory authorities such as the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) require demonstration that generic products achieve comparable systemic exposure to reference products, typically within the 80–125% equivalence interval for AUC and Cmax.¹,²

In Africa, regulatory systems are undergoing a transition toward more rigorous, evidence-based evaluation of generic medicines, supported by continental initiatives such as the African Medicines Agency (AMA) and regional harmonisation programmes.³ This shift is accompanied by increasing requirements for locally relevant BE data and reduced reliance on external regulatory decisions.

Despite these advances, a critical challenge persists: a substantial proportion of BE study failures is attributable not to deficiencies in formulation quality but to suboptimal study design. This distinction has important implications for regulatory science, pharmaceutical development, and access to medicines.

Bioequivalence Beyond Metrics

Bioequivalence is typically assessed using pharmacokinetic (PK) parameters such as AUC and Cmax. However, these parameters are not intrinsic constants; rather, they are influenced by multiple design-related factors, including sampling schedules, subject selection, study conditions (fed versus fasted), and analytical methods.⁴

Consequently, BE outcomes are not solely reflective of the drug product’s physicochemical properties but are also co-determined by methodological design choices. Regulatory guidance from the World Health Organization (WHO) explicitly recognises that study design must be sufficiently sensitive to detect differences between formulations.⁵

This perspective reframes BE from a purely analytical exercise to a construct of experimental design, where methodological rigor directly determines interpretability.

Study Design and Variability

Design Selection

The two-period, two-sequence crossover design remains the gold standard for BE studies due to its ability to minimise inter-subject variability.¹ However, its applicability is limited in specific scenarios, including drugs with long elimination half-lives, safety concerns, or high intra-subject variability.

Highly variable drugs (HVDs), defined as those with intra-subject variability exceeding 30%, present a particular challenge.⁶ In such cases, standard BE designs may lack sufficient power to demonstrate equivalence, even when products are truly bioequivalent.

Regulatory agencies recommend alternative approaches, including replicate crossover designs and reference-scaled average bioequivalence (RSABE), to address this issue.² Failure to adopt appropriate designs for HVDs often results in false-negative outcomes, repeated studies, and increased development costs.

Statistical Power and Sample Size

Sample size determination is a critical component of BE study design, directly influencing the probability of demonstrating equivalence. Underpowered studies may fail to meet equivalence criteria despite true similarity between products, while overpowered studies raise ethical concerns related to unnecessary exposure of participants.⁷

Optimal sample size calculations must incorporate anticipated variability, study design, and regulatory acceptance limits. This requires advanced statistical expertise and highlights the importance of integrating biostatistics early in study planning.

Dissolution Testing and Biowaiver Strategies

In situations where in vivo BE studies are waived, study design extends into the domain of in vitro testing. Dissolution studies must be carefully designed to ensure physiological relevance and discriminatory power.

The similarity factor (f2) is commonly used to compare dissolution profiles; however, it has recognised limitations, particularly in the presence of high variability or non-linear dissolution kinetics.⁸ Regulatory guidance increasingly emphasises a weight-of-evidence approach that integrates dissolution data with biopharmaceutic classification and formulation characteristics.⁵

Poorly designed dissolution studies can undermine otherwise robust biowaiver applications, leading to regulatory rejection.

Comparator Selection and Regulatory Context

The selection of an appropriate reference product is a critical yet frequently underestimated aspect of BE study design. Regulatory requirements vary across jurisdictions, and in African contexts, multiple reference sources (e.g., EU-approved, US-approved, or WHO-prequalified products) may be acceptable.

Misalignment between comparator selection and regulatory expectations can invalidate BE studies, irrespective of their scientific quality. This underscores the need for strategic regulatory planning alongside technical expertise.

Implications for Africa: Study Design as a Barrier to Access

As African regulatory authorities increasingly require BE data for generic drug approval, the capacity to design and conduct robust studies becomes a key determinant of market access.³

Inadequate study design contributes to:

• Delayed product approvals
• Increased development costs
• Reduced availability of affordable medicines

These challenges are particularly significant in the context of rising burdens of non-communicable diseases, where timely access to quality-assured generics is essential.

Bridging the Capacity Gap

While infrastructure for BE studies is expanding across Africa, expertise in advanced study design, variability management, and regulatory strategy remains limited. Addressing this gap requires targeted capacity-building initiatives that integrate clinical pharmacology, biostatistics, and regulatory science.

Collaborative efforts involving regulators, industry, and academia are essential to develop a shared understanding of BE principles and their practical application in African contexts.

Conclusion

Bioequivalence studies are often viewed as technical exercises in regulatory compliance. However, this editorial argues that they should be understood as strategic scientific endeavours, in which study design determines not only the study’s outcome but also the trajectory of product development and access to medicines.

In Africa’s evolving regulatory landscape, strengthening expertise in BE study design is not merely a technical priority; it is a public health imperative.

Study design is not a procedural step in bioequivalence; it is its foundation. Without a robust design, the promise of generic medicines cannot be fully realised.

References

1. European Medicines Agency. Guideline on the investigation of bioequivalence. London: EMA; 2010.
2. US Food and Drug Administration. Bioequivalence studies with pharmacokinetic endpoints for drugs submitted under an ANDA. Silver Spring, MD: FDA; 2014.
3. Ndomondo-Sigonda M, Miot J, Naidoo S, et al. Medicines regulation in Africa: current state and opportunities. BMJ Glob Health. 2017;2(2):e000297.
4. Midha KK, Rawson MJ, Hubbard JW. The bioequivalence of highly variable drugs and drug products. Int J Clin Pharmacol Ther. 2005;43(10):485–98.
5. World Health Organization. Multisource (generic) pharmaceutical products: guidelines on registration requirements to establish interchangeability. Geneva: WHO; 2021.
6. Davit BM, Conner DP, Fabian-Fritsch B, et al. Highly variable drugs: observations from bioequivalence data submitted to the FDA. AAPS J. 2008;10(1):148–56.
7. Chow SC, Liu JP. Design and analysis of bioavailability and bioequivalence studies. 3rd ed. Boca Raton: CRC Press; 2008.
8. Shah VP, Tsong Y, Sathe P, Liu JP. In vitro dissolution profile comparison—statistics and analysis of the similarity factor, f2. Pharm Res. 1998;15(6):889–96.

Our fifth webinar explores the architecture behind access. “Designing Access to Medicines in Africa” brings together regulatory, scientific, and policy expertise to examine how bioequivalence study design shapes market entry for generics across the continent.

As African regulators strengthen requirements, decisions made at the protocol stage—on variability, sample size, comparator selection, and biowaiver strategy—are increasingly determinative. On Tuesday, 10 March 2026, this March Briefing asks what it takes to align rigorous standards with timely access, and how countries can build the technical depth needed to ensure both.

Tuesday, 10 March 2026

Register here: https://us06web.zoom.us/webinar/register/WN_JzfBuffHQa6uG_qC60zWMA