Real-World Outcomes of Baricitinib in Patients with Rheumatoid Arthritis: A Two-Year Observational Study of Overall and Difficult-to-Treat Patients in Japan.

OBJECTIVES: This study aimed to evaluate real-world effectiveness and long-term retention of baricitinib in Japanese patients with rheumatoid arthritis (RA), including those classified as difficult-to-treat (D2T). METHODS: This 24-month observational study enrolled patients initiating baricitinib, stratified by prior use of biological/targeted synthetic disease-modifying antirheumatic drugs (b/tsDMARDs) and baseline Clinical Disease Activity Index (CDAI) scores. Key endpoints included time-to-discontinuation, achievement of and time to low disease activity (LDA) or remission. Data were analysed using logistic regression models adjusted for demographic and clinical variables. RESULTS: Baricitinib demonstrated sustained effectiveness, with 58.2% of overall patients (N=353) and 42.0% of patients with D2T RA (N=88) remaining on treatment at 24 months. CDAI remission was achieved in 36.4% of overall patients and 22.9% patients with D2T RA. Discontinuation was mainly due to primary non-response (11.0%). Mean (SD) changes in patient-reported outcomes (PROs) from baseline scores were: patient global assessment of disease activity (-21.7 [28.4] mm), Health Assessment Questionnaire-Disability Index (-0.360 [0.601]), and pain visual analogue scale (-24.9 [26.8] mm). Among baseline glucocorticoid users retained on baricitinib at 24 months, 55.9% discontinued glucocorticoids. CONCLUSION: Baricitinib showed sustained effectiveness and retention, including in patients with D2T RA; early improvements in pain and fatigue were predictive of CDAI disease remission during the 24-month follow-up.