Background Tumour necrosis factor (TNF)-inhibiting therapy increases the risk of serious infections in rheumatoid arthritis (RA). However, it is not clear whether this risk differs between TNF inhibitors.

Objective To analyse whether the risk of serious infections in patients with RA treated with an anti-TNF inhibitor is different for adalimumab, infliximab and etanercept.

Methods Data from the Dutch RA monitoring registry were used. Incidence rates were calculated from the observed number of first serious infections and follow-up time up to 5 years. A Cox proportional hazards model with time-to-first-serious infection was used to estimate risk differences among the anti-TNF treatment groups, with correction for confounders.

Results The unadjusted incidence rate of a first serious infection in patients with RA per 100 patient-years was 2.61 (95% CI 2.21 to 3.00) for adalimumab, 3.86 (95% CI 3.33 to 4.40) for infliximab and 1.66 (95% CI 1.09 to 2.23) for etanercept. Age, year of starting anti-TNF therapy, comorbidities at baseline and disease activity score 28 over time were included as confounders. No difference in risk for serious infections was found between adalimumab and infliximab with an adjusted HR (adjHR) of 0.90 (95% CI 0.55 to 1.48). The risk of serious infections was significantly lower in etanercept than in both infliximab (adjHR=0.49 (95% CI 0.29 to 0.83)) and adalimumab (adjHR=0.55 (95% CI 0.44 to 0.67)).

Conclusions The risk of serious infections in patients with RA treated with adalimumab or infliximab was similar, while the risk of serious infections in patients with RA treated with etanercept was lower than with both adalimumab and infliximab.