Sex differences in the effectiveness of first-line tumour necrosis factor inhibitors in axial spondyloarthritis: Results from the EuroSpA Research Collaboration Network

Objective: Evidence indicates reduced treatment effectiveness of TNFi in women with axial spondyloarthritis (axSpA) compared with men. We aimed to investigate sex differences in treatment response and retention rates over 24 months of follow-up in axSpA patients initiating their first TNFi. Methods: Data from axSpA patients initiating a TNFi in 1 of 15 registries within EuroSpA collaboration were pooled. We investigated the association of sex with treatment response using logistic regression. The primary outcome was clinically important improvement (CII) at 6 months according to Ankylosing Spondylitis Disease Activity Score with C-reactive protein (CRP) (≥1.1 decrease). We adjusted for age, country and TNFi start year. A secondary outcome was retention rates over 24 months of follow-up assessed by Kaplan-Meier estimator. Results: In total, 6451 axSpA patients with data on CII were assessed for treatment response; 2538 (39%) were women and 3913 (61%) were men. Women presented at baseline with lower CRP levels but had higher scores on patient-reported outcome measures. At 6 months, 53% of the women and 66% of the men had CII. Women had a lower relative risk of CII compared with men (0.81; 95% CI 0.77 to 0.84). This sex difference was similar in adjusted analysis (0.85; 95% CI 0.82 to 0.88). Retention rates were evaluated in 27 702 patients. The TNFi 6/12/24 months retention rates were significantly lower among women (79%/66%/53%) than men (88%/79%/69%). Conclusion: Treatment response and retention rates are lower among women with axSpA initiating their first TNFi. Sex differences in treatment effectiveness were present regardless of the outcome measure used for treatment response, and differences in retention rates transpired early and increased as time progressed.