Therapeutic drug monitoring of infliximab in spondyloarthritis: an observational open-label study.

BACKGROUND: Infliximab is a chimeric monoclonal antibody that binds to human tumor necrosis factor alpha and which is approved for refractory spondyloarthritis (SpA). Individual adjustment of infliximab dosage may help to improve the therapeutic response in SpA. We investigated whether a knowledge of infliximab serum concentration modifies physician decision and improves the control of disease activity in SpA. METHODS: Thirty-two patients routinely treated with infliximab were included in an observational open-label study. On visit 1 (V1), according to disease activity, a preliminary therapeutic decision was selected among 4 therapeutic options (ie, decrease, increase, maintain the dosage of infliximab, or switch over for another treatment), and a blood sample was collected to measure infliximab trough serum concentration. The final therapeutic decision, based on both disease activity and infliximab serum concentration assessed at V1, was applied at the following infusion (V2). Clinical and biological evaluations were performed at V3 and V4 and compared with those at V1. RESULTS: The measurement of infliximab trough concentration modified the therapeutic decision for 10 patients (31%). For both patients with increased or decreased infliximab dosage at V2, median Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) was similar at V3 or V4 as compared with that at V1. However, a trend for an inverse relationship between infliximab serum concentrations and BASDAI was observed. CONCLUSIONS: Knowledge of infliximab trough concentration modified the therapeutic decision for SpA patients with predominantly axial symptoms but did not improve the control of disease activity as estimated by the BASDAI.

Infliximab concentration monitoring improves the control of disease activity in rheumatoid arthritis.

INTRODUCTION: Adjustment of infliximab dosage for individuals may be useful in improving therapeutic response in rheumatoid arthritis (RA). Herein, we aimed to determine whether measurement of infliximab serum concentration modifies the therapeutic decision and improves the control of disease activity. METHODS: RA patients routinely treated with infliximab were included in an observational open-label study. On visit 1 (V1), according to the disease activity, a preliminary therapeutic decision was selected among four therapeutic options and a blood sample was collected to measure trough serum infliximab concentration. The final therapeutic decision, based on both disease activity and serum infliximab concentration assessed at V1, was applied at the following infusion (V2). Clinical and biological evaluations were performed at V3 and V4 and compared with those at V1. RESULTS: We included 24 patients. The final therapeutic decision differed from the preliminary decision for 12 patients (50%). For patients with increased infliximab dosage at V2, mean disease activity score for 28 joints (DAS28) decreased by about 20% at V3 or V4 as compared with V1 (P < 0.05). Decreased DAS28 was correlated with increased serum infliximab concentration (P < 0.02). CONCLUSIONS: The measurement of infliximab trough concentration modifies the therapeutic decision for RA patients and helps improve control of disease activity. Therapeutic drug monitoring of infliximab in RA may be useful for individual dosage adjustment.