Background According to national guidelines issued in 2015, a non-medical switch from originator infliximab (IFX) to biosimilar IFX was conducted in all Danish patients with inflammatory rheumatic diseases treated in routine care.
Objectives To investigate effects of the switch on serum (s) IFX and anti-drug antibodies (ADA) in patients with rheumatoid arthritis (RA), axial spondyloarthrits (SpA) and psoriatic arthritis (PsA).
Methods We included originator infliximab treated patients, who switched to and were treated with biosimiilar infliximab for >2 months with 2 available trough level serum samples (baseline immediately before switching/follow-up 2–4 months after switching time of 2nd–4th infusion). Patients stopping treatment earlier were not included. Trough sIFX <3mg/l was considered low and ≤1mg/l very low. If sIFX <5mg/l, ADA was measured. ADA ≤30AU/l was considered low and ADA >30AU/l median-high. sIFX and ADA were analyzed using automated in-house assays at OUS-Radiumhospitalet. Characteristics and outcomes were registered in the DANBIO registry. Remission was defined by disease activity indices (DAS28 <2.6 (RA, PsA) and ASDAS <1.3 (SpA)). Comparisons were by Mann Whitney U test (unpaired) and Wilcoxon signed rank test (paired). Outcomes are shown as medians (interquartile ranges).
Results 96 pts (192 samples) from 4 departments (49 RA, 27 SpA, 10 PsA, 10 other) were included (age 52 (43–62) years, 47% women). Previous IFX treatment duration was 7.5 (5.1–10.3) years. Follow-up was after 81 (71–90) days. 58 patients (60%) received concomitant methotrexate (15 (10–20) mg/wk). Baseline IFX dose was 3.1 (3.0–4.8) mg/kg every 7 (6–9) weeks. At baseline, 60% of pts had low sIFX and 29% very low and at follow-up it was 57% and 29%, respectively. At baseline, 14 pts (15%) had medium-high ADA, at follow up 16%. Median sIFX was lower at baseline vs. follow-up (1.8 (0.8–5.8) vs 2.4 (0.8–6.2) mg/l, p=0.006) whereas ADA were similar (p=0.7). Six of 58 pts with low baseline sIFX had high sIFX at follow-up, and 3 of 38 pts with high baseline sIFX had low sIFX at follow-up. Similar numbers for low vs. medium–high ADA at baseline and follow-up were 2/81 and 3/15. For the rest, sIFX and ADA remained stable between baseline and follow-up in 87/96 (91%) and 91/96 (95%), respectively (Figure). MTX use was not associated with sIFX or ADA (both p>0.05). Patients with low sIFX received lower IFX doses than pts with sIFX ≥3mg/l (255 (200–320) mg vs. 300 (250–400) mg, p=0.02) and with longer intervals (8 (6–10) weeks vs. 6 (6–6)weeks, p<0.01). Remission rates at baseline (56%/11%/75%) or follow-up (52%/21%/100%) for RA/SpA/PsA were not associated with sIFX (all p>0.05).
Conclusions In this highly selected group of patients treated with originator infliximab for >5 years, non-medical switch to biosimilar IFX had no negative impact on sIFX or ADA 2–4 months following switch. At baseline, 60% of patients had low sIFX but few patients had ADA, perhaps indicating low immunogenicity in these patients.
Disclosure of Interest None declared