Association between disease activity and risk of serious infections in subjects with rheumatoid arthritis treated with etanercept or disease-modifying anti-rheumatic drugs.

Objectives: To determine the risk of serious infection in patients with rheumatoid arthritis (RA) receiving etanercept (ETN) or disease-modifying anti-rheumatic drugs (DMARDs) and to identify factors that predict a higher risk.

Methods: Five-year data from the British Society of Rheumatology Biologics Register (BSRBR), a prospective observational study of patients with active RA treated with ETN, were used. These data were compared with a cohort of patients receiving DMARDs with active RA.

Results: Total follow-up was 19,964 patient-years (py; ETN, 14,381 py; DMARDs, 5583 py). Over the study period, 651 first-recorded serious infections were reported (ETN, 469 [39.9 per 1000 py]; DMARDs, 182 [35.0 per 1000 py]). Overall the risk of serious infection was similar for the 2 treatments; however, in the first 6 months of treatment the hazard ratio (HR) was higher in the ETN than the DMARD group (1.979; p=0.015). A linear association was observed between the serious infection rate and disease-activity score in 28 joints (DAS28) in patients from each treatment group and overall (DAS28 <4, 27.1 per 1000 py; DAS28 ≥8, 64.4 per 1000 py; 7.5% increase in serious infection for each unit increase of DAS28 score at baseline). In a time-dependent analysis, a DAS28 change of 1 unit during follow-up predicted a 27% increase in serious infection rates.

Conclusions: No significant increase in the risk of serious infection was observed with ETN versus DMARDs over the 5-year study; a linear relationship existed between the serious infection rate and disease activity, as measured by DAS28.