JAK Inhibitors for Rheumatoid Arthritis

With Pfizer's Xeljanz (tofacitinib) already on the market for rheumatoid arthritis (RA), two investigational JAK inhibitors, baricitinib (JAK1/2 inhibitor) and filgotinib (selective JAK1 inhibitor), are in late stage development. With larger datasets slowly emerging, this post will be a placeholder to provide updated data and, within reason, head-to-head comparisons.


RA-Build versus DARWIN 1

These two trials are in moderate to severe RA patients who continue on their background conventional disease modifying anti-rheumatic drug (cDMARD) in addition to the investigational drug. Both exclude prior use of biologic DMARDs (bDMARD), namely anti-TNF drugs such as adalimumab. Provided below are some relevant trial inclusion and exclusion criteria to better understand the comparison:


RA-Build (Baricitinib sponsored by Incyte / Eli Lilly)

Inclusion Criteria

  • Have a diagnosis of adult-onset RA as defined by the American College of Rheumatology/ European League Against Rheumatism (ACR/EULAR) 2010 Criteria for the Classification of RA
  • Have moderately to severely active RA defined as the presence of at least 6/68 tender joints and at least 6/66 swollen joints
  • Have a C-reactive protein (CRP) or high-sensitivity C-reactive protein (hsCRP) measurement ≥1.2 times the upper limit of normal (ULN)
  • Have had an insufficient response or are intolerant to cDMARDs and either:
    • Have had regular use of a cDMARD for at least the 12 weeks prior to study entry with a continuous, nonchanging dose for at least 8 weeks prior to study entry
    • For participants not receiving a cDMARD at the time of entry, the investigator will document in the participant's history that the participant had failed, was unable to tolerate, or had a contraindication to treatment with a cDMARD


Exclusion Criteria

  • Are currently receiving corticosteroids at doses >10 mg per day of prednisone (or equivalent) or have been receiving an unstable dosing regimen of corticosteroids within 2 weeks of study entry or within 6 weeks of planned randomization
  • Have started treatment with non-steroidal anti-inflammatory drugs (NSAIDs) or have been receiving an unstable dosing regimen of NSAIDs within 2 weeks of study entry or within 6 weeks of planned randomization
  • Are currently receiving concomitant treatment with methotrexate (MTX), hydroxychloroquine, and sulfasalazine or combination of any 3 cDMARDs
  • Have ever received any biologic DMARD

See full trial details here.


DARWIN 1 (Filgotinib sponsored by Galapagos)

Inclusion Criteria

  •  have a diagnosis of RA since at least 6 months and meeting the 2010 ACR/EULAR criteria of RA and ACR functional class I-III
  • have ≥6 swollen joints (from a 66 joint count) and ≥8 tender joints (from a 68 joint count) at Screening and at Baseline
  • Screening serum CRP ≥0.7 time ULN
  • have received MTX for ≥6 months and have been on a stable dose (15 to 25 mg/week) of MTX for at least 4 weeks prior to Screening and willing to continue on their current regimen for the duration of the study. Stable doses of MTX as low as 10 mg/week are allowed when there is documented evidence of intolerance or safety issues at higher doses.


Exclusion Criteria

  • current therapy with any DMARD other than MTX
  • current or previous RA treatment with a biologic DMARD, with the exception of biologic DMARDs administered in a single clinical study setting more than 6 months prior to Screening (12 months for rituximab or other B cell depleting agents), where the biologic DMARD was effective, and if discontinued, this should not be due to lack of efficacy
  • previous treatment at any time with a cytotoxic agent, other than MTX, before Screening.

See full trial details here.


Below are summarized the 12 week data from RA-Build and DARWIN1, focusing only on the percentage of patients meeting the ACR20, 50 and 70 endpoints. The first two bar graphs include the placebo arm in the respective trials, whereas the third graph compares both datasets with their placebo groups subtracted. The method is an inexact comparison, but is provided as a best approximation for head-to-head comparison. Although once daily and twice daily doses of filgotinib were tested, the two best twice daily doses are plotted. This is in part to simplify the presentation, while being mindful that the twice daily dosing appeared to provide qualitatively improved results for filgotinib. Included in this plot is a best comparison to the percentages achieved by the recommended dose of tofacitinib in Study IV of the tofacitinib registration package. 

RA-Build (12 Weeks Baricitinib)

N = 228, 229, and 227 for placebo, 2mg and 4mg QD respectively.

Data Source at this link. Roll over for the underlying values. 

DARWIN 1 (12 Weeks Filgotinib)

N = 86, 86, 85, and 84 for placebo, 25mg, 50mg and 100mg BID respectively.

Data source at this link (pdf file).

Placebo Adjusted

Note: Baricitinib doses are 2mg and 4mg QD; Filgotinib doses are 50 and 100mg BID; Tofacitinib dose is 5mg BID