Impact of clinical subtype and sex on first-line biologic therapy discontinuation in axial spondyloarthritis

To estimate the main and interaction effects of axial spondyloarthritis (axSpA) subtype and sex on first biologic disease-modifying antirheumatic drug (bDMARD) discontinuation. This retrospective cohort study included nonradiographic axSpA (nr-axSpA) and radiographic axSpA (r-axSpA) patients initiating tumour necrosis factor or interleukin-17 inhibitors. Modified Poisson regressions were used to estimate risk ratios (RRs) for the association of subtype and sex with discontinuation, adjusting for baseline covariates. Interaction was assessed using the relative excess risk due to interaction (RERI) and ratio of RRs. In addition, bDMARD survival rates were analysed using Kaplan-Meier curves. Among 469 patients, 64% discontinued their first bDMARD. Nr-axSpA (RR, 1.80; 95% CI, 1.26-2.59) and female sex (RR, 1.49; 95% CI, 1.081-2.045) were significantly associated with discontinuation. Positive interaction trends between subtype and sex were observed on additive (RERI 0.49, 95% CI, -0.78 to 1.75) and multiplicative (RR ratio, 1.05; 95% CI, 0.55-2.03) scales, though not statistically significant. Nr-axSpA females had twice the discontinuation risk of r-axSpA males (hazard ratio, 2.30; 95% CI, 1.68-3.15, P < .001). bDMARD survival over 20 years was significantly lower in nr-axSpA and female patients. Nr-axSpA and female patients face a significantly higher risk of bDMARD discontinuation and shorter bDMARD survival. Although the combined effect of subtype and sex trended higher, it was not statistically significant. These findings underscore the need to address potential treatment challenges in female nr-axSpA patients.