Related Experiment Video
Updated: Aug 5, 2026

In Vitro Methods for Comparing Target Binding and CDC Induction Between Therapeutic Antibodies: Applications in Biosimilarity Analysis
Published on: May 4, 2017
Increasing formulary adoption of adalimumab biosimilars and differential cost-sharing in Medicare Part D plans
1School of Medicine, University of California San Francisco, San Francisco, California, USA.
Objectives:
Adalimumab was among the first biologics to face widespread biosimilar competition following US market entry of multiple adalimumab biosimilars in 2023. However, Medicare Part D formulary adoption of these products and their associated specialty-tier cost-sharing requirements remain unknown.
Methods:
To evaluate adalimumab biosimilar adoption and associated cost-sharing patterns across Medicare Part D formularies, Centers for Medicare & Medicaid Services (CMS) Medicare Part D Formulary and Plan Benefit Package files were analyzed. Plans were categorized as covering originator adalimumab-only, both originator and biosimilar products (dual coverage), or biosimilars-only.
Results:
In 2023, all Medicare Part D plans covering adalimumab listed only the originator product. By 2024, 52.5% of plans provided dual coverage, increasing to 79.9% in 2025. Biosimilar-exclusive coverage increased from 8.6% of plans in 2025 to 45.9% in 2026, while originator-only coverage declined to 0.8%. Median specialty-tier coinsurance differed according to coverage strategy. In 2026, median specialty-tier coinsurance was 33% among originator-only plans, 27% among dual-coverage plans, and 25% among biosimilar-only plans.
Conclusions:
Medicare Part D formularies rapidly included adalimumab biosimilars following market entry, with substantial growth in biosimilar-exclusive coverage by 2026. Specialty tier coinsurance varied by medication coverage type, suggesting that evolving formulary strategies may influence beneficiary cost-sharing requirements.
Related Concept Videos
Drug Products: Biologics, Biosimilars and Interchangeables
Pharmaceutical Alternatives: Polymorphic Form-Related and Particle Size-Related Therapeutic Nonequivalence
Dosage Regimen: Individualization
Impact of Pharmacokinetic–Pharmacodynamic Models: Regulatory Decisions
Bioequivalence: Overview
Bioavailability: Influencing Factors

