A Randomized, Double-Blind, Placebo-Controlled Confirmatory Study of the Safety and Efficacy of ASP015K in Patients With Rheumatoid Arthritis (RA) Who Had an Inadequate Response or Intolerance to MTX

The purpose of this study is to verify the superiority of ASP015K in combination with MTX or with other disease-modifying antirheumatic drugs (DMARDs) over placebo in terms of efficacy in participants with rheumatoid arthritis (RA) who had an inadequate response or intolerance to MTX, as measured by the American College of Rheumatology (ACR) 20 response rate at Week 24.This study will also evaluate the pharmacokinetics and safety of ASP015K as well as efficacy and safety of long-term treatment with ASP015K (52 weeks).