Peficitinib (ASP015K) is a novel orally bioavailable JAK inhibitor in development for the treatment of RA. It inhibits JAK1, JAK2, JAK3 and Tyk2 enzyme activities and has moderate selectivity or JAK3 inhibition.Here the authors report the findings of a 12-week, randomized, double-blind, placebo-controlled phase IIb study evaluating efficacy, safety and dose response of peficitinib (25, 50, 100, or 150 mg) as once-daily oral monotherapy in Japanese patients with moderate to severe RA. The primar...