Comparison of efficacy between anti-IL-6 receptor antibody and other biological disease-modifying antirheumatic drugs in the patients with rheumatoid arthritis who have knee joint involvement: the ANSWER cohort, retrospective study

Objective We aimed to investigate the efficacy of anti-IL-6 receptor antibody (aIL-6) and other biologic disease-modifying antirheumatic drugs (bDMARDs), such as TNF inhibitor and CTLA4-Ig in the treatment of rheumatoid arthritis (RA) in patients with knee joint involvement. Methods We retrospectively analyzed 1059 treatment courses of patients with RA who visited our hospitals and were treated with bDMARDs. We categorized them into two groups, with or without knee joint involvement. We investigated the clinical disease activity index (CDAI) at baseline and 12 weeks after the initiation of bDMARDs. We compared the improvement of the markers between aIL-6 and other bDMARDs. Results Treatment with aIL-6 significantly increased Delta CDAI (n = 91, 15.4 +/- 1.1; mean +/- SEM) in patients with knee joint involvement, compared to other bDMARDs (n = 232, 11.0 +/- 0.7) at 12 weeks (P = 0.006). Following the multivariate analysis adjusted by the CDAI levels at baseline, age, gender, concomitant use of methotrexate, and the first use of bDMARDs, Delta CDAI levels were significantly higher in aIL-6, compared to other bDMARDs (P = 0.02). However, there was no significant difference in Delta CDAI improvement between aIL-6 (n = 162, 5.9 +/- 0.6) and other bDMARDs (n = 573, 6.2 +/- 0.4) in patients without swollen knee joints. Delta CDAI levels were equally increased in patients with shoulder and elbow joint involvement. Conclusion aIL-6 was more effective in the patients with RA and knee joint involvement, compared to other bDMARDs.