Serum trough infliximab levels: A comparison of three different immunoassays for the monitoring of CT-P13 (infliximab) treatment in patients with inflammatory bowel disease

Background: CT-P13 is a biosimilar drug of reference infliximab and is approved in some countries for use in some indications for which reference infliximab is approved, including inflammatory bowel disease (IBD). The CT-P13 formulation is identical to that of reference infliximab and has similar physiochemical characteristics. However, even a small molecular distinction could lead to different behavior of CT-P13 in immunoanalytical detection systems.

Aim: To determine the correlation between three different enzyme-linked immunosorbent assays for infliximab detection in the measurement of CT-P13 trough serum levels.

Methods: Serum samples (n = 42) from IBD patients (n = 22) treated with CT-P13 Remsima™ (Celltrion, Korea) were evaluated in a blinded way in infliximab assays manufactured by (A) Matriks Biotek (Turkey), (B) Theradiag (France), and (C) R-Biopharm (Germany).

Results: All assays showed excellent qualitative correlation (Cohen's kappa = 0.90 for A vs. B, 0.76 for A vs. C, and 0.83 for B vs. C). A linear quantitative correlation was satisfactory as well (Spearman's r = 0.91 for A vs. B, 0.86 for A vs. C and 0.92 for B vs. C). Assay C did not detect CT-P13 in 6 samples detected by A and/or B.

Conclusion: There is a good correlation of CT-P13 serum level detection between these assays.