To examine the risk of serious infections (SIs) among patients with rheumatoid arthritis (RA) treated with tocilizumab compared with tumor necrosis factor inhibitor (TNFi) in Korea.
We conducted a retrospective cohort study using the Korean National Health Insurance data. The study cohort included patients ≥18 years with RA who were initiated with tocilizumab or TNFi between January 2013 and June 2018. The primary outcome was a composite endpoint of SIs, defined as an infection resulting in intravenous antimicrobial therapy or hospitalization. Secondary outcomes were organ-specific SIs. To control for confounders, we used inverse probability of treatment weighting (IPTW) using propensity score. Hazard ratios (HRs) with 95% confidence intervals (CIs) were estimated using a multivariable Cox regression model.
A total of 8794 patients were identified: 1395 and 7399 patients initiated with tocilizumab and TNFi, respectively. The mean follow-up durations were 1.2 years for tocilizumab initiators and 1.0 year for TNFi initiators. After IPTW and adjustment, no increased risk of SIs was observed in tocilizumab versus TNFi (HR, 1.00; 95%CI, 0.90-1.11). In the secondary analysis, tocilizumab was associated with a higher risk of skin and subcutaneous tissue infections (HR, 1.26; 95%CI, 1.02-1.54) and a lower risk of urological and gynecological infections (HR, 0.65; 95%CI, 0.49-0.87) compared to TNFi.
In this population-based cohort of RA patients in Korea, tocilizumab was not associated with a higher risk of SI compared to TNFi. However, tocilizumab should be carefully used for patients at high risk for skin-related infections.

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