Objectives To examine the impact (if any) of gender on the clinical, functional and patient-reported outcomes of treatment using data pooled from four controlled clinical trials.

Methods Study data were pooled from four clinical control trials in which 1283 adult patients with active ankylosing spondylitis (AS) were treated with etanercept, sulfasalazine or placebo. Patients were stratified by gender and analysed for differences/similarities in baseline demographics, disease characteristics, and efficacy in AS outcome measures and safety and discontinuation rates after 12 weeks of therapy.

Results Significant baseline differences were observed between 326 female patients compared with 957 male patients. Female patients had an older mean age of disease onset (35.0 vs 31.2 years; p<0.001), shorter mean time of disease duration (7.4 vs 9.5 years; p<0.001) and lower mean baseline C-reactive protein (13.1 vs 20.9 mg/l; p<0.001); a lower proportion was HLA-B27 positive (76.3% vs 85.2%; p<0.001) compared with male patients. Women had significantly (p<0.001) smaller differences in all week 12 efficacy assessments including AS disease activity score (0.87 vs −1.08), Bath AS disease activity index (−19.22 vs −23.41) and Bath AS functional index (−13.89 vs −16.88) relative to men. A similar relationship was observed between women and men in the adjusted mean difference of nocturnal back pain (4.04, 95% CI 0.77 to 7.32; p<0.05), total back pain (3.80, 95% CI 0.77 to 7.32; p<0.05) and patient global assessment (4.79, 95% CI 1.51 to 8.08; p<0.01).

Conclusions Women had a higher burden of disease and less improvement in AS outcome measures compared with men. This was observed despite women having a later disease onset of shorter duration; the mechanism behind this observation is unclear. Additional research is necessary to better understand female patients with AS and the burden of disease in this population.