Anti-TNFα drug levels in patients with rheumatoid arthritis and spondyloarthritis

Knowledge of the levels of anti-TNFa drugs can modify treatment in patients with rheumatoid arthritis (RA) and spondyloarthritis (SpA).To compare the levels of anti-TNFa in patients with RA vs SpA, in different clinical situations.A retrospective, observational study was conducted. Levels of anti-TNFa and the presence of anti-drug antibodies were measured in consecutively selected patients, using the ELISA technique.Fifty-three, 73 and 78 patients treated with infliximab, adalimumab and etanercept were studied, respectively. The median drug levels in patients using standard doses were infliximab 2.2 µg/mL (1.4-5.2), adalimumab 4.9 µg/mL (0.8-8.9) and etanercept 3.1 µg/mL (2.3-4.4). There were no differences in drug levels according to disease activity but we found differences in etanercept and infliximab levels according to DMARD use.Levels of anti-TNFa drugs will change with DMARD treatment.