Serious infection across biologic-treated patients with rheumatoid arthritis: results from the British Society for Rheumatology Biologics Register for Rheumatoid Arthritis

Objectives To compare the incidence of serious infection (SI) across biologic drugs used to treat rheumatoid arthritis (RA) using data from the British Society for Rheumatology Biologics Register for Rheumatoid Arthritis (BSRBR-RA). Methods The BSRBR-RA is a prospective observational cohort study. This analysis included patients with RA starting a new biologic. The primary outcome was SI defined as an infectious event requiring admission to hospital, intravenous antibiotics or resulting in death. Event rates were calculated and compared across biologics using Cox proportional hazards with adjustment for potential confounders. Secondary outcomes were the rate of infection by organ class and 30-day mortality following infection. Results This analysis included 19282 patients with 46771 years of follow-up. The incidence of SI was 5.51 cases per 100 patient years for the entire cohort (95%CI 5.29 to 5.71). Compared with etanercept, tocilizumab had a higher risk of SI (HR 1.22, 95% CI 1.02 to 1.47) and certolizumab pegol a lower risk of SI (HR 0.75, 95% CI 0.58 to 0.97) in the fully adjusted model. The 30-day mortality following SI was 10.4% (95% CI 9.2% to 11.6%). Conclusions The rate of SI was lower with certolizumab pegol than etanercept in the primary analysis but the result was no longer significant in several sensitivity analyses performed suggesting residual confounding may account for the observed difference. From these results, it would be wrong to conclude that certolizumab pegol has a lower rate of SI than other biologics; however, the risk does not appear to be significantly higher as has previously been suggested.