Rationale, Design and Methods of the Filgotinib Initial Response Study in Rheumatoid Arthritis (FIRST-RA).

introductionFilgotinib is an oral Janus kinase 1 (JAK1) preferential inhibitor approved for adult patients with moderate-to-severe active rheumatoid arthritis (RA) who have responded inadequately to, or who are intolerant of, one or more disease-modifying antirheumatic drugs (DMARDs). While randomised trials have demonstrated its efficacy and tolerability, real-world data on very early treatment effects-particularly on pain relief, fatigue and function-remain scarce. The FIRST-RA study was initiated to address this evidence gap under routine care conditions.

methodsFIRST-RA is a prospective, multicentre, non-interventional cohort study in Germany and Austria. Approximately 300 adult patients with RA newly starting filgotinib are enrolled and followed for 24 weeks. Patients are stratified into three groups based on prior use of advanced therapies (AT; biologic [b]DMARDs or targeted synthetic [ts]DMARDs): AT-naïve, one prior AT and ≥ 2 prior ATs. Clinical assessments are conducted at baseline and weeks 4, 12 and 24. Patient-reported outcomes (PROs), including the Rheumatoid Arthritis Impact of Disease (RAID) questionnaire, are captured electronically or on paper- daily during week 1 and at regular intervals thereafter. PLANNED OUTCOMES: The primary endpoint is the change in RAID pain score from baseline to week 4 (or earlier). Secondary endpoints include fatigue, disease activity, morning stiffness, treatment satisfaction and tolerability. Additional analyses will investigate very early symptom changes, drug utilisation patterns and treatment persistence, as well as effectiveness within AT exposure subgroups (AT-naïve and AT-experienced), summarised descriptively without formal subgroup testing. An exploratory, descriptive analysis will examine how the 2023 label update for JAK inhibitors may have influenced patient characteristics, prescribing patterns and safety outcomes, using the earlier-enrolled FILOSOPHY real-world cohort as an external reference. FIRST-RA is the first real-world study to capture very early symptomatic responses to filgotinib. By integrating PRO data with clinical outcomes, the study aims to support personalised RA management and clarify the use of filgotinib in today's clinical practice. STUDY REGISTRATION: German Clinical Trials Register, DRKS0003613.