Immunoglobulin-G dynamics and relation to antibiotic prescriptions in multiple sclerosis patients treated with rituximab: a real-world cohort

• Long-term rituximab treatment causes a significant, dose-dependent decline in IgG. • Cumulative dose is a stronger predictor of IgG decline than dose intensity. • Low IgG levels did not predict an increased risk of antibiotic prescriptions. • Female sex and higher disability at baseline predicted increased antibiotic use. • Routine IgG monitoring is warranted, especially in older patients with high exposure. Rituximab, a B-cell-depleting therapy widely used for multiple sclerosis (MS), is associated with a progressive decline in immunoglobulin G (IgG) levels, raising concerns regarding infection risk. This study evaluates IgG dynamics and antibiotic use in a real-world MS cohort. A retrospective cohort study was conducted on MS patients treated with Rituximab over a 10-year period. Patients included had at least two infusions and a follow-up of ≥6 months after the last infusion. IgG levels and antibiotic prescriptions were registered longitudinally. The study included 213 patients (72% female, mean age 40.1 ± 10.6 years). Mean IgG decreased from 11.5 ± 2.4 g/L at baseline to 9.0 ± 1.7 g/L after five years, with an average decline of 0.35 g/L/year (95% CI 0.25–0.44; p