How Useful is Anti-TNF Serum Level and Anti-drug Antibodies Detectionin Evaluating Patients with Spondyloarthritis?

Objective: The aim of this study was to assess whether infliximab and adalimumab drug serum levels and the detection of anti-drug antibodies can be of use in better observing disease activity in patients with spondyloarthritis, besides classical tools such as BASDAI, ASDAS and inflammatory markers. We proposed to evaluate the influence of ADA in non-responders and in drug-related adverse events. Methods: Over one year, we enrolled 115 patients with SpA, treated with infliximab or adalimumab. Patients who delayed prescribed drug administration were excluded from the study cohort. The population comprised 69 patients - 33 on IFX and 35 on ADA. NSAIDs administration was recommended “on demand”. Demographic, clinical (BASDAI, ASDAS) and laboratory (ESR, CRP) data was collected together with drug serum level and anti-drug antibodies using ELISA. The statistical analysis was performed using the SPSS software, version 20.0 with the aid of Student t-test, Spearman and Pearson tests. Results: Detectable IFX serum levels were identified in 60% of patients while 40% had undetectable drug titers. The IFX-negative had significantly higher disease activity scores: BASDAI (P=0.023), ASDAS-ESR (P<0.001) and ASDAS-CRP (P<0.001). Significant differences were found in the same subgroups regarding inflammatory markers, with higher ESR (P<0.001) and CRP (P=0.032) in patients with undetectable IFX levels. When measuring ADL serum levels, 82% had detectable drug concentrations, with lower BASDAI (P<0.001), ASDAS-ESR and ASDASCRP (P<0.001) and higher ESR and CRP at collection time when compared to ADL-negative patients. NSAID consumption correlated to undetectable levels of IFX and ADL as well as with anti-drug antibodies for both IFX and ADL positivity. All patients who experienced drug related adverse events on both IFX and ADL had positive anti-drug antibodies. Conclusion: Serum drug level measurement and anti-drug antibody detection can be used as a completion of a clinician’s tools in assessing disease activity, leading to an optimal patient management.