Counting the costs: a nationwide study on healthcare use following an adalimumab biosimilar switch in >1300 inflammatory arthritis patients.

Background: In Denmark, cost savings motivate mandatory biosimilar switches. In 2018, patients switched from originator to biosimilar adalimumab, that is, to GP2017 in Eastern and to SB5 in Western Denmark. However, concerns were raised about additional costs covering, that is, an increased number of outpatient visits due to patient education, treatment monitoring, and patient concerns.

Objectives: To investigate whether the switch led to increased total healthcare costs, defined as costs related to in- and outpatient contacts in hospitals and the primary sector and use of prescription medicine (excluding biological treatment).

Design: Observational cohort study with geographical cluster pseudo-randomization.

Methods: Patients with rheumatoid arthritis, psoriatic arthritis (PsA), and axial spondyloarthritis (AxSpA), who switched were identified in the nationwide DANBIO registry. Total healthcare costs 9 months before and after the switch were captured from the National Patient and Prescription registries. The difference between pre- and post-switch costs was estimated by a generalized estimation equations (GEE) model.

Results: Overall, 1316 patients switched to GP2017 (n = 621) or SB5 (n = 695). Total healthcare costs were mainly driven by hospital costs. The monthly fluctuations of hospital costs 9 months before and after the switch were largely similar or decreased. In the adjusted analyses (GEE), hospital costs decreased after the switch (by approximately 15%) for GP2017 switchers, especially PsA (estimate = 0.83; 95% CI 0.75-0.92) and AxSpA patients (estimate = 0.85; 0.77-0.93), with no significant changes for SB5 switchers.

Conclusion: We found no increase in total healthcare costs in 9 months following a nationwide mandatory adalimumab originator to biosimilar switch. Our findings were strengthened by similar results for GP2017 and SB5.