Emery P, Durez P, Hueber AJ, et al. - An extensive program of clinical studies of patients with moderate-to-severe rheumatoid arthritis (RA) has demonstrated the effectiveness and good tolerability of baricitinib, an oral selective inhibitor of Janus kinase (JAK)1 and JAK2, in the treatment of RA. In a phase 2b dose-ranging study of baricitinib in combination with traditional disease-modifying antirheumatic drugs (DMARDs) in RA patients, baricitinib 2 mg or 4 mg once daily was identified providing dose-dependent suppression of synovitis, osteitis, erosion and cartilage loss at weeks 12 and 24 vs placebo in magnetic resonance imaging. These findings linked with clinical outcomes and validation of these findings was done in three phase 3 studies (RA-BEGIN, RA-BEAM and RA-BUILD) utilizing X-rays to assess structural joint damage. Preclinical studies supported the findings from the phase 3 studies of patients with RA, which indicated that baricitinib has an osteoprotective effect, increasing mineralisation in bone-forming cells. Inhibition of radiographic joint damage progression was observed with administration of baricitinib 4 mg once daily to patients with moderate-to-severe RA who are naïve to DMARDs or respond inadequately to csDMARDs, including methotrexate, and the beneficial effects are similar to those noted with adalimumab.