POS0376 DOES A MANDATORY SWITCH FROM ORIGINATOR ADALIMUMAB TO BIOSIMILAR GP2017 OR SB5 LEAD TO INCREASED HOSPITAL COSTS? A DANBIO STUDY OF >1,300 PATIENTS WITH INFLAMMATORY ARTHRITIS

Background
In 2018, Danish national guidelines dictated a mandatory switch from originator to biosimilar adalimumab based on geographical residence, i.e., GP2017 in Eastern regions and SB5 in Western regions of Denmark[1]. The switch was motivated by cost savings (approx. 34-49%). Concerns were raised if hospitals would encounter additional costs as a result of increased numbers of outpatient visits/contacts (due to patient concerns, education, treatment monitoring).

Objectives
To investigate if the switch from originator to either of the adalimumab biosimilars led to increased hospital costs, defined as all in- and outpatient contacts.

Methods
Observational cohort study with surrogate cluster (i.e. geographical) pseudo-randomization. Patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA) or axial spondyloartritis (AxSpA), who performed an adalimumab biosimilar switch were identified in the rheumatology registry, DANBIO. Hospital contacts were identified through linkage to the National Patient Registry. Hospital costs (based on DRG tariffs) were reported 9 months pre- and post-switch. In addition, the difference between pre- and postswitch costs was estimated by a generalized estimation equations (GEE) model. Medication costs of adalimumab originator and biosimilars were not available, and thus not included in the model.

Results
1,318 patients were included (51% male, mean disease duration 16 years) and switched to either GP2017 (n=621) or SB5 (n=695). Baseline characteristics for both treatment groups stratified by diagnosis are given in Table 1. Monthly hospital costs 9 months pre- and post-switch were largely similar or decreased post-switch (Figure 1). No increase was found in the adjusted analyses (GEE); hospital costs decreased post-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), whereas no significant changes were found for SB5 switchers.

Conclusion
In this study of >1,300 patient with inflammatory arthritis, we found no sign of increased healthcare hospital costs 9 months following a nationwide mandatory adalimumab originator to biosimilar switch. Our findings were strengthened by similar results regardless of whether patients switched to GP2017 or SB5.