To explore acceptance and retention rate of biosimilar CT-P13 after switching from originator infliximab (OI) in patients with various rheumatic diseases.

Patients with stable rheumatoid arthritis (RA), ankylosing spondylitis (AS) or psoriatic arthritis (PsA) under OI were proposed to switch to CT-P13 at the same regimen. A prospective cohort of infliximab-naïve patients beginning CT-P13 and a retrospective cohort of patients treated with OI were used as controls. The primary outcome was to evaluate the retention rate of CT-P13. Secondary outcomes were the switch acceptance rate, reasons of failure and safety.

Switch was proposed to 100 patients and accepted by 89 of them (63 AS, 12 PsA and 14 RA). After a median follow-up of 33 weeks, 72% of patients were still treated with CT-P13. This retention rate was significantly lower than the one found in our retrospective and prospective control cohorts: 88% and 90% respectively (P-value=0.0002). Within patients who asked to be reswitched to OI, 13/25 (52%) presented clinical disease activity, one developed serum sickness and 11 (44%) presented no objective activity. A subanalysis excluding these 11 patients abrogated difference in retention rates between the 3 cohorts (P-value=0.453). After reswitching to OI, patients without objective disease activity claimed to recover original efficacy.

Retention rate was lower after switching from OI to CT-P13 compared to our control cohorts. However, this difference faded after excluding patients without objective clinical activity, suggesting a reluctance of patients to the switch and a negative perception of the biosimilar.