Discontinuation of biosimilar infliximab in Japanese patients with rheumatoid arthritis achieving sustained clinical remission or low disease activity during the IFX-SIRIUS STUDY I (the IFX-SIRIUS STUDY II): A clinical, ultrasound, and biomarker-based effectiveness after discontinuation and reinitiation of biosimilar infliximab.

Rheumatoid arthritis (RA) is a chronic inflammatory disease affecting synovial joints. Biosimilar disease-modifying anti-rheumatic drugs offer cost-effective alternatives to originator biologics for RA treatment but remain expensive for long-term use. This prospective study investigated the clinical benefit of discontinuing CT-P13, a biosimilar of infliximab, in RA patients maintaining clinical remission or low disease activity. Five patients were enrolled from the IFX-SIRIUS STUDY I. CT-P13 was discontinued for 48 weeks, with evaluation using clinical indices, musculoskeletal ultrasound (MSUS), and serum biomarkers. Two patients experienced clinical relapse at weeks 5 and 36. The patient who relapsed at week 36 was re-administered CT-P13 and showed improved clinical outcomes without adverse events. Patients with non-clinical relapse showed no changes in disease activity scores or MSUS scores, with no notable alterations in serum cytokine levels. Over 50% of the patients maintained non-clinical relapse after CT-P13 discontinuation, and relapsed patients improved after re-administration without adverse events. This study was registered in the Japan Registry of Clinical Trials (https://jrct.mhlw.go.jp) on April 20, 2020, as jRCTs071200007.