Antimicrobial use and serious infections among psoriatic arthritis patients after initiating tumor necrosis factor inhibitors: a nationwide matched cohort study.

OBJECTIVE To analyse antimicrobial use and serious infections (SI) among psoriatic arthritis (PsA) patients before and after initiating TNF inhibitor (TNFi) treatment. METHODS In this nationwide matched cohort study, we extracted data on PsA patients initiating TNFi from 2005 to 2018 from the ICEBIO registry and matched them by age, sex, and calendar time to five randomly selected comparators from the general population. All filled prescriptions for antimicrobials, glucocorticoids, and methotrexate two years before and after initiating TNFi treatment were extracted from the Icelandic Prescription Medicines Register. All infection-related hospitalisations, a proxy for SI, were extracted from the Icelandic Hospital Discharge Register. RESULTS The study included 399 PsA patients and 1,986 matched comparators. Patients received more antimicrobial prescriptions before TNFi treatment, with a mean number of prescriptions (NP) per year of 1.26 vs. 0.60 (p<0.001). The mean NP increased to 1.64 (p<0.001) in the 12 months following TNFi initiation but returned to baseline thereafter. No statistically significant increase in SI was found. Adjusted for covariates, PsA patients had HR of 1.43 (95% CI 1.18-1.72, p<0.001) for receiving a prescription for antimicrobials following TNFi treatment initiation compared to themselves before TNFi treatment. The risk was increased in the first year after treatment initiation but not in the second year, suggesting a transient effect. CONCLUSION Following TNFi initiation, antimicrobial use rose temporarily, with no significant increase in SI. These results support the safety of TNFi in PsA management and the risk of SI should not weigh heavily in treatment decisions.