Probability of Response in the First Sixteen Weeks After Starting Biologics: An Analysis of Juvenile Idiopathic Arthritis Biologics Trials.

Objectives: Most juvenile idiopathic arthritis (JIA) biologic disease‐modifying antirheumatic drugs (bDMARDs) trials used an open‐label run‐in period followed by randomized medication withdrawal. We used data from the run‐in period of 4 bDMARD trials to 1) delineate early response trajectory to bDMARDs and 2) identify predictors of early response. Methods: Data from the first 16 weeks of 4 bDMARD trials were used. The primary outcome was the American College of Rheumatology (ACR) Pediatric 50 (Pedi 50) response criteria: clinically significant response defined as ACR Pedi 50 or greater. The secondary outcome was the clinical Juvenile Arthritis Disease Activity Score in 10 joints (cJADAS10) minimal disease activity state. Response transition rates and predictors were modeled using an inhomogeneous Markov multistate model. Results: Five hundred thirty‐two participants (70% receiving methotrexate, 41% prednisone) were included. By month 4, the probability of attaining ACR Pedi 50 or greater was 0.698. If ACR Pedi 50 or more was not achieved by month 1, the probability of achieving it by month 4 was 0.60. If ACR Pedi 50 or more was not achieved by month 3, the probability of achieving this by month 4 was 0.31. Age at diagnosis, disease duration, baseline rheumatoid factor, and active joint counts predicted ACR and cJADAS state transitions, adjusted for concomitant treatment. Conclusions: No response ACR Pedi 50 or more by month 1 after treatment was associated with a 0.60 probability of responding by month 4, but not responding by month 3 was associated with a 0.31 probability of response by month 4. Baseline disease duration, rheumatoid factor, and active joint counts predicted early treatment response (ACR and cJADAS10 states). [ABSTRACT FROM AUTHOR]