The efficacy of infliximab in treating rheumatoid arthritis depends on its serum trough concentration, which must be maintained at a minimum of 1 µg/mL to achieve the desired effects. However, Japan's National Health Insurance system does not cover tests for rheumatoid arthritis patients undergoing treatment with biosimilar infliximab because its performance as a biosimilar remains unclear. This study aimed to investigate whether the Remi-check Q qualitative assay yields comparable results for biosimilar infliximab and the originator product. Infliximab BS 100 "NK" and Remicade 100® were separately diluted in pooled human serum to yield test samples at the following concentrations: 0.30, 0.70, 1.20, and 3.00 µg/mL. Prepared samples were quantitatively assessed using an enzyme-linked immunosorbent assay (ELISA) and qualitatively using Remi-check Q, and the results obtained for the originator and biosimilar product were compared. For both originator and biosimilar infliximab, Remi-check Q yielded a negative result for all 0.30 and 0.70 µg/mL samples and a positive result for all 3.00 µg/mL samples. However, negative results were obtained with a fraction of the 1.20 µg/mL samples (biosimilar, 4/15; originator, 3/15). Concurrence rates between the results of quantitative ELISA and qualitative Remi-check Q analyses were comparable between originator and biosimilar infliximab at all tested concentrations. These results indicate that Remi-check Q yields comparable results for biosimilar infliximab and the originator product on being used as a qualitative assay for trough serum levels.
Keywords: biosimilar; infliximab; originator; quick determining kit; rheumatoid arthritis; trough serum level.