A Study to Evaluate Efficacy and Safety of ASP015K in Patients With Rheumatoid Arthritis (RA) Who Had an Inadequate Response to Methotrexate (MTX) Treatment

This study was a multi-center, randomized, placebo-controlled, double-blind, parallel-group, confirmatory study to evaluate the efficacy and safety of ASP015K (100 and 150 mg/day) administered in combination with MTX in participants with RA who had an inadequate response to MTX. Participants orally received ASP015K 100 mg, ASP015K 150 mg or placebo once daily (QD) in combination with MTX after breakfast for 52 weeks. At Week 12, inadequate responders in the placebo group, as determined by a \< 20% improvement from baseline (i.e., treatment initiation day) in tender or painful joint count (TJC) and swollen joint count (SJC), were switched to either ASP015K 100 mg or ASP015K 150 mg, and the dosage was maintained until the end of treatment (EOT). In addition, participants who received placebo at Week 28 were switched to either ASP015K 100 mg or ASP015K 150 mg, and the dosage was maintained until the EOT. The ASP015K dose that was started for placebo group participants at Week 12 or Week 28 was randomly chosen at baseline. The dose was switched under the blinded condition. Participants who completed this study were eligible for participation in the open-label extension study (015K-CL-RAJ2). Participants made a follow-up visit after the week 52 visit if they did not enroll into the extension study on the day of the week 52 visit.