Effectiveness and Drug Survival of TNF Inhibitors in the Treatment of Ankylosing Spondylitis: A Prospective Cohort Study

Objective. The aim of this research was to describe the effectiveness and drug survival of tumor necrosis factor (TNF) inhibitors in the treatment of ankylosing spondylitis (AS) and to analyze the effect of concomitant treatment with conventional disease-modifying antirheumatic drugs. Methods. Patients with AS identified from the National Register for Biologic Treatment in Finland starting their first TNF inhibitor treatment between July 2004 and December 2011 were included. Treatment response was measured as an improvement of 50% (or 20 mm) after 6 months of treatment onset compared to the baseline Bath AS Disease Activity Index (BASDAI) score. Treatment response and 2-year drug survival were modeled with logistic regression and time-dependent Cox proportional hazard models, respectively. Results. The study comprised 543 patients, of whom 123 also commenced a second TNF inhibitor during the followup. Treatment was discontinued within 24 months by 25% and 28% of the users of the first and the second TNF inhibitors, respectively. BASDAI response at 6 months was achieved by 52% and 25% of the users of the first and the second TNF inhibitors, respectively. Etanercept (ETN; HR 0.42, 95% CI 0.29-0.62) and adalimumab (ADA; HR 0.48, 95% CI 0.30-0.77) were associated with better drug survival in comparison to infliximab (IFX). Also, concurrent use of sulfasalazine (SSZ; HR 0.70, 95% CI 0.49-0.99) decreased the hazard for treatment discontinuation. Conclusion. TNF inhibitors are equipotent in the treatment of AS; however, ETN and ADA were found superior to IFX in drug survival. The use of SSZ improves treatment continuation.