Designing Biosimilar Phase 1 Trials: PK, PD, and Immunogenicity Considerations

Introduction

Biosimilars—biologic products that are highly similar to an approved reference product—must undergo rigorous evaluation to demonstrate similarity in structure, function, and clinical performance. Phase 1 clinical trials are a cornerstone of biosimilar development and focus primarily on pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity. These studies are not designed to establish efficacy per se but to confirm that the biosimilar behaves similarly to the originator biologic in healthy subjects or patients. This tutorial explains the strategic design and regulatory expectations for Phase 1 biosimilar trials.

Why Phase 1 Studies Are Critical for Biosimilars

• To demonstrate PK equivalence to the reference biologic
• To assess PD markers where available (e.g., ANC for filgrastim)
• To evaluate the incidence and severity of anti-drug antibodies (ADAs)
• To establish bioequivalence margins for regulatory approval

Regulatory Framework for Biosimilar Phase 1 Trials

FDA Guidance

• “Scientific Considerations in Demonstrating Biosimilarity to a Reference Product”
• Recommends single-dose, crossover or parallel design with PK/PD endpoints

EMA Requirements

• Requires comparative PK and PD (if feasible) with justification of study design
• Separate immunogenicity assessment over a suitable follow-up period

CDSCO (India)

• Follows the 2016 Guidelines on Similar Biologics
• Mandates comparative PK and immunogenicity before Phase 3 waiver or approval

Study Design for PK/PD Assessment

Study Type

• Parallel-group design: Used when half-life is long (e.g., monoclonal antibodies)
• Crossover design: Preferred for short-acting products like insulin or filgrastim

Subject Population

• Healthy volunteers: Preferred to reduce variability
• Patients: Required if the biologic has safety risks in healthy subjects

Dose and Route

• Use the same dose, route, and formulation as the reference biologic
• Conduct under fasting or standardized conditions

Sample Size

• Powered to detect a 20% difference in key PK parameters (Cmax, AUC)
• Typically 40–100 subjects, depending on variability and design

Pharmacokinetic Endpoints

Primary PK Parameters

• Cmax: Maximum plasma concentration
• AUC_0–t: Area under the curve to last measurable concentration
• AUC_0–∞: Total exposure

PK Acceptance Range

• 90% Confidence Interval: Must fall within 80%–125% for Cmax and AUC
• Use log-transformed data and ANOVA or mixed-effects models

Pharmacodynamic Endpoints

PD endpoints are used when they are well-established and sensitive to detect differences.

Examples:

• ANC (absolute neutrophil count) for G-CSF
• Glucose infusion rate for insulin
• Coagulation markers for biosimilar clotting factors

Immunogenicity Assessment

Key Components:

• Screening for anti-drug antibodies (ADA) before and after dosing
• Characterization of binding and neutralizing antibodies
• Monitoring for clinical impact (loss of efficacy, hypersensitivity)

Study Duration

• Longer follow-up required—up to 12 weeks or more—to detect delayed immune response
• Sampling at Day 0, Day 14, Day 28, and Day 56 or longer

Assay Validation

• Use sensitive and validated ELISA or cell-based assays
• Assess specificity, sensitivity, and drug tolerance

Statistical Considerations

Bioequivalence Analysis

• Use geometric mean ratio (biosimilar/reference)
• Report 90% CI for both Cmax and AUC parameters
• Exclude subjects with ADA positivity from PK analysis (if predefined)

PD Analysis

• Non-inferiority or equivalence analysis for PD markers
• PD/PK correlation plots to demonstrate parallelism

Documentation and Reporting

Clinical Study Report (CSR)

• Include population demographics, PK/PD plots, and ADA tables
• Discuss any differences in exposure, half-life, or immune response

Investigator’s Brochure (IB)

• Summarize comparative data, assay methods, and justification of similarity

Regulatory Dossier

• Module 5.3.1.2: PK/PD study data
• Module 2.7.1: Summary of biopharmaceutics

Best Practices for Phase 1 Biosimilar Studies

• Select most sensitive population for PK/PD comparability
• Ensure matching dosage form and administration with reference
• Plan for ADA handling and re-testing procedures
• Standardize assay methods and storage protocols
• Justify any ethnic or formulation-related differences