Background/Purpose: Spondyloarthritides, a heterogeneous group of chronic, inflammatory disorders with overlapping organ and joint targeting, share the same therapeutic approach in regard to biological therapy. Anti-tumor necrosis factor (anti-TNF) agents have highly proved their efficacy in lowering overall disease activity. However, a number of patients who initially responded to therapy fail to maintain a satisfactory disease evolution curve. Loss of response to TNF-inhibitors in spondyloarthritis (SpA) might be due to undetectable drug serum level. Determining infliximab (IFX) serum levels in SpA patients and adjusting dose or interval administration in a personalized manner might lead to a better disease outcome.

Methods: During a period of six months (January – June 2015), thirty-three consecutive patients with established SpA were enrolled in this study, while on regular hospital visit for IFX infusion. Patient data was gathered together with serum drug levels measured by enzyme linked immunosorbent assay (ELISA), using Progenika kits (Promonitor-IFX). The statistical analysis was performed using the SPSS statistical software, version 20.0, with a standardized p value of 0.05. Differences between groups were recorded with the aid of Student t-test, whereas Spearman test was used for correlations.

Results: Out of the 33 enrolled patients (90% males; mean age 37.8 years), all presented HLA B27 antigen positivity. Mean disease duration was 89 months (SD +/- 56). Detectable IFX serum levels were measured in 60% of patients (20 patients) while 40% (13 patients) had unmeasurable drug titers. The latter had significantly higher disease activity scores such as BASDAI (mean 3.01, p .023), ASDAS-ESR (mean 2.77, p .000) and ASDAS-CRP (mean 2.48, p .001) when compared to patients with detectable serum drug (1.52, 1.39 and 1.34 respectively). Inflammatory markers determined at the same visit showed higher ESR and CRP levels in IFX-negative patients (mean ESR 37 versus 9.5 with laboratory reference values ranging 2-20 mm/h, p .000; mean CRP 25 versus 4 with normal values between 0 to 5 mg/L, p.032). Serum IFX detection correlated to ASDAS scores (r -.583 p .000 for ASDAS-ESR; r -.512 p .002 for ASDAS-CRP) and to inflammatory biomarkers (r -.607 p .000 for ESR; r -.573 p .000 for CRP). In the IFX-positive group, mean drug persistence was of 64 (SD +/-32.5) months while lower for the IFX-negative group (45 months, SD +/- 21.7, p .066), the time frame being positively correlated to drug detection (r .352, p .045). Treatment persistence also correlated to disease duration (r .719, p .000). Dosage regimen was not significantly different between the two groups (5.11mg/kg in undetectable IFX group compared to 5mg/kg for the second group) and the maintenance drug administration interval, whether at 6 or 8 weeks, positively correlated to quantitative serum IFX levels.

Conclusion: In our study, IFX serum level correlated with patient’s disease activity measured through ASDAS score. Moreover, correlations to inflammatory tests highlight their importance on follow-up visits. Monitoring IFX levels might represent a useful tool in assessing patients’ evolution.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/infliximab-in-spondyloarthritis-patients-utility-of-drug-level-monitoring/