Designing Biosimilar Clinical Studies: Navigating Global Regulatory Expectations

Introduction

The biosimilar landscape is entering a pivotal phase. According to a 2025 IQVIA report, 118 biologics are expected to lose U.S. patent protection by 2034, representing more than $200 billion in market opportunity, yet nearly 90% currently lack a biosimilar development pipeline due to one fundamental challenge: designing a clinical comparability program that satisfies increasingly sophisticated global regulatory expectations.

For pharmaceutical companies, this creates both urgency and complexity in developing biosimilars. Much of this challenge stems from designing studies that align with regulatory expectations while maximizing sensitivity to detect clinically meaningful differences between products. This blog focuses on how to design biosimilar studies across major regulatory guidelines, highlighting where their key criteria align, where differences matter, and how these considerations translate into practice through a benralizumab case study.

Section 1: Global Regulatory Expectations for Biosimilar Study Design

Unlike small-molecule drugs used in traditional BE studies, biologics are large and complex molecules that require a more comprehensive assessment of similarity, including PK, PD, safety, and immunogenicity.

Across global regulatory agencies, a shared principle is the use of a stepwise approach to reduce uncertainty in establishing biosimilarity. This begins with analytical and non-clinical evaluation to clinical comparability, though non-clinical components are outside the scope of this article. While analytical characterization establishes structural and functional similarity, the clinical program is ultimately responsible for demonstrating no clinically meaningful differences between the biosimilar and reference product. Although regulatory agencies generally align on the clinical evaluation, differences emerge in how these expectations are applied to study design, population selection, dose strategy, and endpoint selection. Across these domains, a common principle emerges: biosimilar studies should be designed to maximize sensitivity for detecting differences between products.

This blog examines guidelines from major regulatory agencies, including the World Health Organization (WHO), Food and Drug Administration (FDA), European Medicines Agency (EMA), Pharmaceutical Drug Directorate (PDD) (Health Canada), Pharmaceuticals and  Medical Devices Agency (PMDA), National Medical Products Administration (NMPA), Ministration of Food and Drug Safety (MFDS), and Central Drugs Standard Control Organization (CDSCO).

Choice of Reference Product

As in standard BE studies, biosimilar clinical development begins with selecting an appropriate reference product. Globally, there is broad consensus that the reference product should be a locally approved and licensed biologic. Some regulatory agencies also prohibit the use of another biosimilar as the reference product; for example, both the MFDS and CDSCO explicitly state this requirement. Under EMA requirements, the reference product should be authorized within the EU market.

In practice, reference product selection extends beyond regulatory requirements. The underlying challenge is ensuring that reference product sourcing supports a globally acceptable comparability package while minimizing bridging studies that can lengthen development timelines.

Study Design

Study design should be optimized to detect clinically meaningful differences between products. Regulatory agencies generally align on the use of a single-dose crossover design as it is often the most sensitive approach for detecting PK differences while reducing variability and sample size. It is the preferred approach for biologics with short half-lives, rapid PD responses, and low risk of immunogenicity. The FDA, for example, defines a short half-life in this context as less than five days.

However, biologics introduce additional considerations beyond those encountered in traditional BE studies. For biologics with longer half-lives or a higher potential for immunogenic responses, parallel designs are often preferred due to concerns about carryover risks and immune responses that may alter PK or PD profiles. A multiple-dose design may also be appropriate when the PD effect is delayed or when single-dose PK profiles are insufficient to characterize the PK/PD relationship.

Ultimately, the design should balance sensitivity, immunogenicity risk, and operational considerations.

Study Population

As biologics are highly complex molecules with the potential for target-mediated effects and immunogenic responses, the selected population must be sufficiently sensitive to detect subtle differences between biosimilar and reference product. Regulatory agencies generally recommend selecting the most sensitive population for detecting differences in PK and PD while minimizing confounding sources of variability. The WHO further recommends standardizing key demographic factors such as ethnicity, body weight, and sex.

In practice, healthy volunteers are typically preferred when ethically feasible, due to their controlled setting for detecting differences, whereas disease-related factors in patient populations may alter clearance, receptor-mediated disposition, and immunogenicity-related exposure profiles. However, studies in healthy participants may not always be appropriate for biologics with significant safety concerns, elevated immunogenicity risk, or PD markers that are only relevant in patients. In these situations, clinical studies, often involving multiple-dose administration, should be conducted in the target patient population. For biologics approved across multiple indications, regulators generally recommend selecting the condition most sensitive for detecting differences between products.

Dose Selection

As many biologics exhibit non-linear PK, target-mediated drug disposition, or receptor saturation across the therapeutic range, regulatory agencies generally emphasize the importance of considering PK linearity across the dose-response curve when selecting an appropriate dose.

Across regulatory agencies, the FDA, NMPA, and MFDS view dose selection through the lens of sensitivity rather than therapeutic relevance. They generally favor doses positioned on the steep portion of the exposure-response curve as they provide greater sensitivity in healthy participants. At these doses, small differences in exposure may result in more detectable changes in PK or PD response before receptor saturation obscures potential distinctions.

Other agencies take slightly different approaches: the WHO and CDSCO recommend doses within the therapeutic range, whereas the EMA and PDD support the use of sub-therapeutic dosing in healthy participants when appropriately justified.

Route of Administration

When only one route of administration exists for the reference product, the biosimilar should match the same route. When multiple routes are available, regulatory agencies generally prefer non-intravenous (IV) routes, such as subcutaneous (SC) administration, because extravascular delivery is often more sensitive for detecting differences between biologics, and may provide insight into local tolerability and PK profiles related to ADME (absorption, distribution, metabolism and elimination). The EMA, PMDA, and MFDS specifically address products with both IV and SC administration, noting that evaluation of the IV route may be waived if comparable absorption and elimination have been demonstrated for the SC route. However, such waivers must be scientifically justified, particularly for biologics exhibiting complex absorption characteristics or flip-flop kinetics, where the absorption rate is slower than the elimination rate and therefore becomes the rate-limiting determinant of the observed PK profile.

PK Parameters

While regulatory agencies agree on assessing biosimilarity based on the rate and extent of absorption, they differ in the specific PK parameters required. The FDA, EMA, and MFDS recommend AUC_0-inf for IV studies, whereas both AUC and C_max are considered primary endpoints for SC studies because extravascular administration introduces an absorption phase that may contribute to differences in systemic exposure. Similarly, the WHO, PDD, and PMDA also emphasize AUC and C_max, although AUC may be defined as AUC_0-t, or left unspecified depending on study design. The NMPA and CDSCO take a less prescriptive approach, focusing on rate and extent of absorption without explicitly defining the primary PK parameters, though these are typically reflected by AUC and C_max in practice.

Secondary PK parameters show greater variability across agencies. The EMA and MFDS recommend measures such as time to maximum concentration (T_max), volume of distribution, and half-life (T_1/2), while the WHO includes additional parameters such as residual area and terminal elimination rate constant (λ). The NMPA and CDSCO emphasize clearance and elimination half-life to support biosimilarity.

For multiple-dose studies, there is more alignment: the FDA, EMA, and MFDS recommend steady-state AUC over the dosing interval (AUC_0-tau,ss) as the primary endpoint, with steady-state trough concentration (C_trough,ss) and C_max,ss as secondary endpoints.

PD Biomarkers

Evaluation of PD biomarkers can strengthen the totality of evidence for biosimilarity. While regulatory expectations vary, there is general consensus that PD biomarkers should be scientifically justified and relevant to the mechanism of action or clinical endpoints. The FDA further specifies that biomarkers should demonstrate a clear relationship to dosing (onset and return to baseline), exhibit an adequate dynamic range, be sensitive enough to detect differences between the biosimilar and reference product, and be measured using well-validated assays. Regulatory agencies also provide examples of appropriate PD endpoints, such as the euglycemic clamp test for insulin products and absolute neutrophil count for granulocyte colony-simulating factor (G-CSF). The WHO further emphasizes the value of mechanism-based biomarkers for certain biologics when they are sufficiently sensitive and clinically relevant.

Comparative PK/PD Study

One of the most significant shifts in biosimilar regulations over the last decade has been the decreasing reliance on comparative efficacy studies (CES). As a result, sponsors increasingly invest in clinical pharmacology strategies that can reduce the need for large and costly CES. Regulatory agencies broadly agree that combined PK and PD assessments should be conducted synchronously when feasible, providing a more sensitive characterization of the PK-PD relationship by directly linking systemic exposure to pharmacologic response. Consequently, agencies increasingly recognize that a CES may not be required if the totality of evidence –including comparative analytical characterization, non-clinical assessment, PK/PD, safety, and immunogenicity data–collectively demonstrates biosimilarity.

The FDA, EMA, PDD and MFDS generally allow waiver of a CES when robust PK/PD evaluation adequately addresses residual uncertainty. Other agencies, such as the WHO, PMDA, NMPA, and CDSCO place greater emphasis on the totality of evidence without explicitly defining criteria for waiving a CES; in some cases, such as with CDSCO, a phase III comparative trial may still be required if uncertainty remains.

Overall, a well-designed development program that integrates PK, PD, safety, and immunogenicity can strengthen the case for waiving a CES while demonstrating biosimilarity.

Biosimilarity Criteria

Although the conventional equivalence range of 80.00% to 125.00% for the 90% confidence interval of the geometric mean ratio is widely accepted for PK endpoints across regulatory agencies, assessment of PD similarity may require additional scientific justification. Unlike PK parameters, acceptance criteria for PD endpoints should be predefined and scientifically justified based on assay performance, biomarker variability/ sensitivity, clinical relevance, and the expected exposure-response relationship.

For PK endpoints, the FDA, WHO, and PMDA endorse the conventional 80.00% to 125.00% equivalence range, while allowing applicants to predefine and justify alternative acceptance limits for PD endpoints. The PDD and MFDS also emphasize the evaluation of elimination-related parameters, recognizing that biologics may exhibit target-mediated disposition, non-linear PK, prolonged half-life, or immunogenicity-related effects that influence comparative assessment.

In contrast, the NMPA and CDSCO take a less prescriptive approach, recommending comparison of parameters reflecting both absorption and elimination, without explicitly specifying equivalence ranges. Overall, although most agencies align on the 80.00% to 125.00% range, interpretation of biosimilarity is beyond statistical equivalence alone and should be considered within the broader context.

Safety and Immunogenicity

Comparative safety and immunogenicity assessments are central components of biosimilar development because even minor differences in biologic structure, formulation, or manufacturing processes may alter immune responses and potentially affect clinical comparability between products. Regulatory agencies are aligned in requiring a comparative assessment of the type, frequency, and severity of adverse events between the products, with particular emphasis on known adverse reactions described in the reference biologics as well as any risks potentially arising from product-related differences.

Importantly, immunogenicity assessment is no longer viewed as an isolated endpoint, especially when anti-drug antibodies (ADA) may alter drug exposure, neutralizing biologic activity, accelerate clearance, or affect downstream PD responses and safety profiles. As a result, immunogenicity evaluation is typically integrated into PK, PD, and safety studies, with the primary objective of ruling out clinically meaningful differences in immune response between products. Across agencies, immunogenicity evaluations are expected to be comparative, scientifically justified to characterize both the incidence and clinical impact of ADA formation on PK, PD, safety, and efficacy.

The EMA, WHO, and PDD provide more detailed guidance, recommending evaluation of ADA incidence, titers, and neutralizing antibody activity, as well as the temporal onset of immune response. They also emphasize assessing the downstream impact of ADA on safety, PK, and PD between ADA-positive and ADA-negative participants.

 

Section 2: Biosimilar Case Study

To illustrate these concepts, this section presents an example clinical pharmacology strategy for a proposed benralizumab (FASENRA^®) biosimilar (Table 1). Benralizumab’s prolonged half-life, mechanism-based PD response through eosinophil depletion, and the potential impact of anti-drug antibodies on drug disposition make it a representative monoclonal antibody model for biosimilar development. Together, these characteristics underscore the importance of integrating PK, PD, safety, and immunogenicity assessments when designing biosimilar studies.

The benralizumab example is provided for illustrative purposes only. Final biosimilar study design should be based on the totality of evidence, including analytical similarity, non-clinical findings, PK/PD characteristics, safety considerations, immunogenicity risk, and the expectations of the target regulatory authority.

Table 1: Illustrative Biosimilar Development Strategy for a Benralizumab Biosimilar

Biosimilar Development Consideration	Example Approach	Scientific Rationale
Study Design	Parallel	Benralizumab’s prolonged half-life (15.5 days) and potential for treatment-induced immunogenicity favor a parallel design, as residual exposure and immune responses may compromise the interpretability of crossover comparisons.
Study Population	Healthy male and female volunteers	For monoclonal antibodies, disease-related factors such as target expression, inflammatory burden, and immune activation may influence PK, PD response, and immunogenicity. A healthy population may therefore provide greater sensitivity to detect subtle differences between the proposed biosimilar and reference product.
Sensitive Dose Selection	30 mg, single dose	The approved 30 mg dose provides clinically relevant exposure for PK comparability and aligns with the approved dosing regimen. Although eosinophil depletion may approach maximal response at this dose, it remains appropriate for PK assessment, with PD findings interpreted within the overall biosimilarity framework.
PK Parameters	AUC0-inf, AUC0-t, Cmax as primary endpoints; Clearance, half-lives and other disposition parameters as supportive endpoints.	AUC and Cmax serve as the primary PK endpoints for demonstrating comparable systemic exposure, while supportive parameters may provide additional insights into differences in elimination pathways influenced by immunogenicity or other biologic-specific mechanisms.
PD Biomarkers	Blood eosinophil counts	Blood eosinophil depletion is a mechanism-based biomarker directly linked to IL-5Rα blockade, and the rapid PD response observed following a single dose supports characterization of pharmacologic activity. However, as near-complete eosinophil depletion may occur at therapeutic doses, the biomarker may exhibit limited dynamic range for detecting subtle differences between products and should therefore be interpreted within the broader context.
PK/PD Study	Exposure-response characterizations	Characterization of the exposure-response relationship between benralizumab concentrations and eosinophil depletion provides orthogonal evidence of comparable pharmacologic activity and reduces residual uncertainty within the biosimilarity assessment.
Biosimilarity Criteria	90% CIs of the geometric mean ratios of the predefined PK parameters within conventional equivalence margins.   PD endpoints, such as eosinophil depletion AUEC, may be included as supportive evidence when the biomarker demonstrates sufficient sensitivity.	As eosinophil depletion may approach maximal response at therapeutic doses, PD assessments are most informative when interpreted alongside PK, safety and immunogenicity findings.
Safety	Comparison of adverse event type, incidence, and severity.	Comparative safety assessment contributes to the totality of evidence and helps confirm that any residual uncertainty following analytical, PK, and PD similarity assessment does not result in clinically meaningful differences in clinical performance.
Immunogenicity	Comparison of ADA incidence, titer, and neutralizing antibody responses, including evaluation of potential effects on PK, PD, and safety.	As ADA formation has been associated with increased benralizumab clearance and attenuation of PD effect, comparative immunogenicity assessment is important for determining whether immune responses differentially influence exposure, PD, or safety between the proposed biosimilar and reference product.

 

Why You Should Choose BPSI for Your Next Biosimilar Project

As this overview highlights, successful biosimilar development requires study strategies that balance scientific rigor and regulatory expectations. While many study elements may resemble BE studies, their role within the biosimilarity framework is fundamentally different. Together, they provide orthogonal evidence to reduce residual uncertainty and support the demonstration of biosimilarity.

Although global regulatory agencies are broadly aligned on the principles of biosimilarity assessment, study strategies should be tailored to the unique characteristics of each biologic and target regulatory market. Sponsors should integrate these considerations early in clinical pharmacology, biomarker selection, immunogenicity assessment, and regulatory expectations to help streamline development.

At BPSI, we support sponsors throughout all stages of the biosimilar development cycle, from regulatory strategy and study design to clinical execution and data interpretation. Connect with us to discuss your biosimilar development program.

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