According to a recently published Phase IIb, dose-ranging study published in the Journal of Rheumatology, MRI findings can be used to manifest dose-dependent suppression of osteitis and synovitis together with suppression of bone erosion progression in active and erosive RA patients (MTX-IR) within 12 weeks of starting Baricitinib treatment. These MRI findings of Phase IIb study were evaluated to establish dose selection for the Phase III program.

A total of 301 people with active disease and showed inadequate response to MTX(MTX-IR) were selected and categorized 2:1:1:1:1 to obtain placebo or Baricitinib 1-, 2-, 4-, or 8-mg orally one time a day for 24 weeks. Hand/wrist MRI was performed within 154 patients with definitive radiographic erosion at baseline and weeks 12 and 24. Scored images for osteitis, cartilage loss, synovitis, and bone erosion were examined individually by two expert radiologists blinded to treatment and visit order. Total joint damage and combined inflammation scores were also evaluated. Analysis of covariance was used to perform a comparison between treatment groups by adjusting baseline scores. The mean changes from baseline to week 12 for bone erosion and synovitis within participants of placebo, Baricitinib 4-mg, and the Baricitinib 8-mg group found to be were (-0.10, -1.50, and -1.60) and (0.90, 0.10, and 0.40), respectively.

These findings demonstrated the clinical effectiveness of Baricitinib and developed the belief that Baricitinib 4-mg could significantly decrease the radiographic progression in Phase III studies.