Background In previous observational studies of TNF-inhibitors, the proportion of patients achieving sufficient clinical response (BASDAI 50) after six months of treatment onset has ranged from 52% to 63% while 26% to 37% have discontinued the treatment within 24 months [1–3].

Objectives The aim of this research was to describe the effectiveness and drug survival of TNF-inhibitors in the treatment of ankylosing spondylitis (AS) in Finland and to analyze the effect of concomitant treatment with conventional Disease-Modifying Anti-Rheumatic Drugs.

Methods AS patients enrolled in the National Register for Biologic Treatment in Finland (ROB-FIN) 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 BASDAI score. Treatment effectiveness and 2 year drug survival were modelled with logistic regression and time-dependent cox-proportional hazard models, respectively. The results are reported either as Odds Ratios (OR) or Hazard Ratios (HR) where appropriate.

Results The study comprised 543 patients, of which 123 also commenced a second TNF-inhibitor during the follow-up. Treatment was discontinued within 24 months by 24% and 28% of the users of the first and the second TNF-inhibitors, respectively. BASDAI50 response at 6 months was achieved by 52% and 25% of the users of the first and the second TNF-inhibitors, respectively.

Logistic regression analyses revealed no statistically significant differences between TNF-inhibitors or the use of concomitant cDMARDs. Etanercept (HR 0.48, 95% CI 0.31-0.74) and adalimumab (HR 0.52 95% CI 0.30-0.91) were associated with better drug survival in comparison to infliximab. Also, sulfasalazine (HR 0.70 95% CI 0.49-0.99) decreased the hazard for treatment discontinuation.

Conclusions TNF-inhibitors proved equipotent in the treatment of AS, however etanercept and adalimumab were found superior to infliximab in drug survival. Concomitant use of sulfasalazine reduced the hazard for treatment discontinuation possibly by providing a synergistic effectiveness benefit.

References

1. Lord P a C, Farragher TM, Lunt M, et al. Predictors of response to anti-TNF therapy in ankylosing spondylitis: results from the British Society for Rheumatology Biologics Register. Rheumatology 2010;49:563–70.

2. Glintborg B, Ostergaard M, Krogh NS, et al. Predictors of treatment response and drug continuation in 842 patients with ankylosing spondylitis treated with anti-tumour necrosis factor: results from 8 years' surveillance in the Danish nationwide DANBIO registry. Ann Rheum Dis 2010;69:2002–8.

3. Kristensen LE, Karlsson J a, Englund M, et al. 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. Arthritis Care Res 2010;62:1362–9.

Acknowledgements We thank all Finnish rheumatologists for their efforts in the data collection and Pfizer for supporting the study.

Disclosure of Interest None declared