OBJECTIVES: To investigate efficacy and safety of the Janus kinase-1 inhibitor filgotinib in patients with active rheumatoid arthritis (RA) with limited or no prior methotrexate (MTX) exposure.

METHODS: This 52-week, phase 3, multicentre, double-blind clinical trial (NCT02886728) evaluated once-daily oral filgotinib in 1252 patients with RA randomised 2:1:1:2 to filgotinib 200 mg with MTX (FIL200 +MTX), filgotinib 100 mg with MTX (FIL100 +MTX), filgotinib 200 mg monotherapy (FIL200), or MTX. The primary endpoint was proportion achieving 20% improvement in American College of Rheumatology criteria (ACR20) at week 24.

RESULTS: The primary endpoint was achieved by 81% of patients receiving FIL200+ MTX versus 71% receiving MTX (p < 0.001). A significantly greater proportion treated with FIL100+ MTX compared with MTX achieved an ACR20 response (80%, p=0.017) at week 24. Significant improvement in Health Assessment Questionnaire-Disability Index was seen at week 24; least-squares mean change from baseline was -1.0 and -0.94 with FIL200+MTX and FIL100+MTX, respectively, versus -0.81 with MTX (p < 0.001, p=0.008, respectively). Significantly higher proportions receiving FIL200+MTX (54%) and FIL100+MTX (43%) achieved DAS28(CRP) < 2.6 versus MTX (29%) (p < 0.001 for both) at week 24. Hierarchical testing stopped for comparison of ACR20 for FIL200 monotherapy (78%) versus MTX (71%) at week 24 (p=0.058). Adverse event rates through week 52 were comparable between all treatments.

CONCLUSIONS: FIL200+MTX and FIL100+MTX both significantly improved signs and symptoms and physical function in patients with active RA and limited or no prior MTX exposure; FIL200 monotherapy did not have a superior ACR20 response rate versus MTX. Filgotinib was well tolerated, with acceptable safety compared with MTX.