• biosimilar pharmaceuticals
• disease modifying antirheumatic drug
• drug utilization
• evidence based medicine
• rheumatoid arthritis

Aims. This study is aimed at assessing the utilization patterns and the clinical impact of the introduction of infliximab-biosimilar in a central Region of Italy (Tuscany).
Methods. We performed a retrospective population based cohort study on data collected in Tuscan healthcare administrative databases. We included patients with diagnosis of RA, or psoriatic arthritis, or ankylosing spondylitis, or ulcerative colitis (UC), or Crohn’s disease (CD), or psoriasis. The first analysis compared patients treated with infliximab on January 1st, 2013 (originator only available) to those on January 1st, 2016 (originator and biosimilar available). The second analysis compared infliximab-originator users with infliximab-biosimilar ones. Adjusted odds ratios (OR) for persistence on treatment, emergency department (ED) admissions, hospitalizations and specialist visits were calculated.
Results. The first analysis included 606 patients and the second 434. In both analyses, we did not observe any significant difference in persistence. In the first analysis, the 2016 infliximab-originator cohort showed a significant association with the risk of having at least one ED admission (OR 1.54, 95% CI 1.02 to 2.31). A significant difference of accessing a specialist visit (more frequently rheumatologic) was observed in the 2016 cohort (OR 1.52, 95% CI 1.05 to 2.20). In the second analysis, the probability of having at least one hospitalization decreased significantly in switchers to infliximab-biosimilar (OR 0.49, 95% CI 0.26 to 0.96).
Conclusions. Our study showed no relevant changes in the clinical outcomes following the introduction of infliximab-biosimilar. The few differences observed can be explained mainly by a selective switching to infliximab-biosimilar in patients with lower burden of disease.