McCoy, Rozalina G.

Objective The aim of this study was to compare infection‐related hospitalization risk among patients with nonrenal systemic lupus erythematosus initiating commonly used immunosuppressants. Methods We emulated a target trial using Optum Labs Data Warehouse claims to compare the risk of infection‐related hospitalization among patients initiating azathioprine, belimumab, methotrexate, or mycophenolic acid analogues (MPAAs) between March 2011 and September 2023. We excluded patients with prior lupus nephritis, solid‐organ or bone marrow transplantation, or rituximab/cyclophosphamide exposure. The primary outcome was time to first infection‐related hospitalization using intention‐to‐treat (ITT) and per‐protocol (PP) analyses. We applied inverse probability of treatment weighting to account for baseline covariates and fitted marginal structural Cox models incorporating time‐varying monthly glucocorticoid dose during follow‐up. Results Among 6,168 patients, 24‐month cumulative incidence of infection‐related hospitalization was 10% (95% confidence interval [CI] 8–12) for azathioprine, 8% (95% CI 5–10) for belimumab, 10% (95% CI 8–11) for methotrexate, and 13% (95% CI 10–15) for MPAAs. In ITT analyses, MPAAs had higher risk than belimumab (hazard ratio [HR] 1.55, 95% CI 1.07–2.25) and methotrexate (HR 1.32, 95% CI 1.04–1.68). In PP analyses, azathioprine (HR 2.04, 95% CI 1.01–4.16) and MPAAs (HR 2.27, 95% CI 1.11–4.62) had higher risk compared with belimumab. After accounting for time‐varying monthly glucocorticoid dose, between‐treatment differences were no longer significant. Conclusion Initial differences in the infection‐related hospitalization risk were attenuated after accounting for time‐varying glucocorticoid exposure. These findings highlight glucocorticoid exposure as an important factor associated with serious infection risk while recognizing that postbaseline glucocorticoid use may reflect both evolving disease activity and a pathway through which therapies influence infection risk. image