Etanercept Concentration in Patients with Rheumatoid Arthritis and Its Potential Influence on Treatment Decisions: A Pilot Study

Objective. For patients with rheumatoid arthritis (RA), recommendations are inconclusive about whether tumor necrosis factor-alpha (TNF-alpha)-blocker therapy should be evaluated at 3 or 6 months. Biomarkers are needed to predict at 3 months which patients would benefit from further treatment because of nonoptimal response. Our objective was to investigate whether serum etanercept (ETN) concentrations and anti-ETN antibodies at 3 months are predictors of clinical response to ETN at 6 months in patients with RA in terms of European League Against Rheumatism criteria and Disease Activity Score in 28 joints (DAS28). Methods. Between 2009 and 2010, we included 19 women with active RA who were candidates for ETN therapy. Response criteria were evaluated at 3 and 6 months. Serum concentrations of ETN and anti-ETN antibodies were measured by ELISA at baseline and at 3 and 6 months. Results. Eighteen patients completed followup. Three-month ETN concentrations were lower for 6-month nonresponders than responders (p = 0.03). Three-month ETN levels correlated significantly with change in DAS28 between baseline and 6 months (r = -0.62, p = 0.006). The best predictor of response at 6 months was observed with an ETN threshold of 3.1 mu g/ml at 3 months. No anti-ETN antibodies were found. Conclusion. ETN concentrations at 3 months predict response to ETN therapy at 6 months. Low ETN concentrations could explain the absence of response to ETN, suggesting that patients with low ETN levels could benefit from increased ETN dose or earlier interruption of treatment. (First Release July 1 2012; J Rheumatol 2012;39:1533-8; doi:10.3899/jrheum.111522)