Incidence Rates of Infections in Rheumatoid Arthritis Patients Treated with Janus Kinase or Interleukin-6 Inhibitors: Results of a Retrospective, Multicenter Cohort Study

Objective: This study aimed to compare the incidence rates (IRs) of infections, including herpes zoster (HZ), in rheumatoid arthritis (RA) patients treated with Janus kinase inhibitors (JAKis) or interleukin-6 inhibitors (IL-6is). Methods: We retrospectively analyzed 444 RA patients treated using IL-6is (n = 283) or JAKis (n = 161). After adjusting for clinical characteristic imbalances by propensity score matching (PSM), we compared the IRs of infections including HZ between the JAKi and IL-6i groups. Results: Observational period: 1423.93 patient years (PY); median observational period: 2.51 years. After PSM, incidence rate ratios comparing JAKi with IL-6i were 3.45 (95% confidence interval CI: 1.48-9.04) for serious infections other than HZ indicating that the JAKi-treated group was more likely to develop serious infection than the IL-6i-treated group. Multivariate Cox regression analyses revealed that the use of prednisolone > 5.0 mg/day, coexisting interstitial lung disease (ILD), and diabetes mellitus (DM) were independent risk factors for serious infections. The crude IR for HZ was significantly higher in the JAKi group, but the difference between groups was not significant (IRR: 2.83, 95% CI: 0.87-10.96) in PSM analysis. Unadjusted and PSM analyses performed in our study showed increased IRs of serious infections in patients with RA treated with JAKis compared with those treated with IL-6is. Conclusions: The presence of ILD or DM and the use of prednisolone were found to be independent risk factors for serious infection in RA patients treated using JAKis. Whereas the IRs for HZ after PSM were not significantly different between the JAKi and IL-6i groups.