Efficacy of tocilizumab and evaluation of clinical remission as determined by CDAI and MMP-3 level

Tocilizumab, a biological agent developed in Japan, is a human anti-interleukin-6 (anti-IL-6) receptor antibody. Rheumatoid arthritis improves with its use. A remission rate of 59% is attainable, as measured by disease activity score 28 (DAS28) in the SAMURAI study. However, in tocilizumab treatment, C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) levels drop to negative values; therefore we sought to utilize a different index for measuring its efficacy. In order to evaluate the effects of tocilizumab we carried out this study using clinical disease activity index (CDAI), as it is not reliant on blood data and would also allow us to determine which markers are present in remission. Twenty-two patients under treatment with tocilizumab participated in this study. Effects of treatment as well as the remission rate were measured by CDAI and DAS28 3 months after initiation of treatment. IL-6 and matrix metalloproteinase-3 (MMP-3) levels were measured at the same time. We studied the clinical efficacy of tocilizumab using DAS28 after treatment; remission as measured by DAS28 was 57.1% at 1 year. However, the remission rate as measured by CDAI was only 19.1% at 1 year. CDAI was not only correlated with DAS28, but also other clinical variables, MMP-3, and IL-6. We conclude that CDAI is effective in measuring clinical response to tocilizumab treatment, and that MMP-3 level is as useful as IL-6 level as an indicator.