Scripties UMCG - Rijksuniversiteit Groningen
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The association between serum drug level of TNF-α inhibitors and disease activity in patients with axial spondyloarthritis in daily clinical practice.

(2018) Wolff, L. de (Liseth)

Introduction: In approximately 50% of patients with axial spondyloarthritis (SpA) treated with TNF-α inhibitors, treatment loses efficacy. Therefore, the research objective was to investigate the association between serum trough levels of TNF-α inhibitors and disease activity (DA) in axial SpA patients in daily clinical practice.
Material and methods: From June 1st 2015 to June 1st 2016 all 112 patients in the UMCG of the Groningen Leeuwarden Axial SpA (GLAS) cohort on TNF-α inhibitors were approached to have a random serum trough drug level measurement. Secondly, serum trough drug level measurements ordered on clinical grounds between June 1st 2015 to May 1st 2018 of all GLAS patients were analysed. DA was assessed with ea. the Ankylosing Spondylitis Disease Activity Score (ASDAS).
Results: 67 (60%) of the 112 patients approached for a random serum trough level measurement were eligible for analyses. 32 patients (48%) had a therapeutic serum level. No significant differences in patient characteristics between the therapeutic and below-therapeutic group were found. No association between random trough level and DA was found.
41 patients had a serum trough level measurement on clinical grounds: 32 patients (78%) experienced increase in DA. 21 patients (51%) had a therapeutic serum level. Patients with a therapeutic serum level had significantly less often an active disease (63%) than patients with a below-therapeutic serum level (94%) (p<0.05). Furthermore, patients with a below-therapeutic level had a higher increase in disease activity, measured with ΔASDAS, compared to patients with a therapeutic level (p<0.05).
Conclusion: In this group of axial SpA patients serum trough levels of TNF-α inhibitors taken on clinical grounds were associated with disease activity. However, in patients with random measurements, no associations were found.

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