Circulating complexes between tumour necrosis factor‐alpha and etanercept predict long‐term efficacy of etanercept in juvenile idiopathic arthritis

AIM: The relationship between tumour necrosis factor‐alpha (TNF‐α) and drug survival had not been studied in juvenile idiopathic arthritis (JIA), and there were no laboratory tests to predict the long‐term efficacy of biological drugs for JIA. We studied whether serum levels of TNF‐α, free or bound to etanercept, could predict long‐term efficacy of etanercept in children with JIA. METHODS: We included 41 biologic‐naïve patients with JIA who started treatment with etanercept at Skåne University Hospital between 1999 and 2010. Serum taken at the start of treatment and at the six‐week follow‐up were analysed for TNF‐α and the long‐term efficacy of etanercept was assessed using the drug survival time. RESULTS: Levels of TNF‐α increased significantly at the six‐week follow‐up, and this was almost exclusively comprised of TNF‐α in complex with etanercept. The increase in TNF‐α showed a dose‐dependent correlation to long‐term drug survival (p < 0.01). CONCLUSION: Increasing levels of circulating TNF‐α at treatment initiation predicted long‐term efficacy of etanercept in children with JIA, which may have been due to different pathophysiological mechanisms of inflammation. Our result may provide a helpful clinical tool, as high levels of circulating TNF‐α/etanercept complexes could be used as a marker for the long‐term efficacy of etanercept.