Presence of peripheral arthritis and male sex predicting continuation of anti-tumor necrosis factor therapy in ankylosing spondylitis: an observational prospective cohort study from the South Swedish Arthritis Treatment Group Register

Abstract

Objective: To examine clinical characteristics as possible predictors of long-term treatment continuation with adalimumab, etanercept, and infliximab in ankylosing spondylitis (AS) patients who had never taken biologics treated in clinical practice.

Methods: Patients in southern Sweden with active AS starting biologic therapy for the first time between October 1999 and December 2008 (n = 243, 75% men) were included in a structured clinical followup over 2 years. Patients with clinical spondylitis had not responded to at least 2 nonsteroidal antiinflammatory drugs, whereas patients who also had peripheral arthritis (n = 121) had additionally failed at least 1 conventional disease-modifying antirheumatic drug (DMARD) treatment course. The mean ± SD age at inclusion was 43 ± 12 years, with a mean ± SD disease duration prior to treatment of 16 ± 12 years.

Results: The 2-year drug continuation rate was 74%. Male sex (hazard ratio [HR] of premature discontinuation 0.36 [95% confidence interval (95% CI) 0.19-0.68]) and the presence of peripheral arthritis (HR 0.49 [95% CI 0.27-0.88]) were found to be significant predictors of better drug survival. Furthermore, a trend was seen for more favorable drug continuation on treatment with etanercept as compared with infliximab (HR 0.50 [95% CI 0.25-1.04], P = 0.062), whereas no differences were found comparing the 3 anti-tumor necrosis factor agents in other ways. Higher baseline C-reactive protein level (HR 0.99 [95% CI 0.97-1.00], P = 0.12) and concomitant treatment with nonbiologic DMARDs (HR 0.61 [95% CI 0.34-1.10], P = 0.10) also showed trends to entail better drug adherence.

Conclusion: AS patients in this study have an excellent 2-year drug survival rate of 74%. Significant predictors for treatment continuation in this study were male sex and the presence of peripheral arthritis.