Background The goal of rheumatoid arthritis (RA) strategy is to reach remission or at least a low disease activity. When this gaol is reached, no clear guideline exist to manage therapy. Recently, STRASS (Spacing TNF-blocker injections in RA Study) provided evidence of step-down therapeutic strategy with adalimumab or etanercept (1).

Objectives We investigated if drug dosages and their antidrug antibodies (ADAb) could predict relapse during the 18 months of STRASS study.

Methods We assessed 131 serum among the 137 included in STRASS study (60 and 71 for adalimumab and etanercept, respectively). Serum were collected at the time of randomisation. Adalimumab and etanercept blood concentrations and theirs ADAb were assessed by ELISA (Theradiag, Marne-La-Vallee, France). For this study, relapse was defined as DAS28>2.6 with DAS28 increase >0.6 since the previous study visit.

Results Characteristics of the 131 patients similar to 137 from the initial STRASS study (data not shown). The median age was 54.5 [48.3–61.8] years. One hundred and two (77%) were female. The median disease duration was 6.5 [4.5–12.4] years. The median DAS28, ESR, and CRP were 2.0 [1.5–2.3], 10 [6–17], and 3 [2–4]mg/mL, respectively. Methotrexate was the main DMARDs used (n=91; 70%). No baseline characteristics were associated with relapse during tapering or not. In patients treated with etanercept, etanercept level was similar in case of relapse or not. Similarly, adalimumab level was comparable in case of relapse or not. However, in patients treated with adalimumab, ADABs was significantly higher in case of relapse compared to no relapse (0.94±0.27 ng/ml vs. 0.27±0.76 ng/ml; P=0.03, respectively). However, this difference was not clinically pertinent.

Conclusions No difference was observed in adalimumab or etanercept blood level to predict relapse in RA patients with low disease activity. However, a slight increased of ADAb for adalimumab was observed. Its signification needs further investigation.

1. Fautrel B, Pham T, Alfaiate T, et al. Step-down strategy of spacing TNF-blocker injections for established rheumatoid arthritis in remission: results of the multicentre non-inferiority randomised open-label controlled trial (STRASS: Spacing of TNF-blocker injections in Rheumatoid ArthritiS Study). Annals of the Rheumatic Diseases 2016; 75: 59–67.

Acknowledgement AbbVie provided funding for this study. Analysis was performed independently to AbbVie.

Disclosure of Interest None declared