What studies are required to demonstrate biosimilarity?

Biosimilar development follows a stepwise totality-of-evidence approach: 1) Analytical similarity (foundation) - extensive physicochemical characterization comparing biosimilar to reference product; primary structure, higher-order structure, post-translational modifications, purity, aggregates, particles. Functional assays for biological activity. Multiple batches of reference from different markets. 2) Animal studies - comparative PK, toxicity if needed; often abbreviated or waived. 3) Clinical pharmacology - PK/PD similarity studies demonstrating equivalent exposure and response. 4) Clinical efficacy/safety - at least one adequately powered comparative trial in sensitive population demonstrating equivalent efficacy (typically 90% CI within 80-125% margin). 5) Immunogenicity - comparative ADA assessment. Extrapolation to other indications based on mechanism of action and scientific justification. Interchangeability requires additional switching studies in US. Total development: 5-8 years, $100-200M vs $1-2B for new biologics.