Comparative Effectiveness of Mepolizumab and Omalizumab in Patients Eligible for Both: A Retrospective Cohort Study

Background Omalizumab and mepolizumab are effective biologic therapies for severe asthma. However, their comparative effectiveness in patients eligible for both treatments remains unclear in routine care. Therefore, the aim of this study was to compare the real-world efficacies of mepolizumab and omalizumab in these patients. Methods This retrospective cohort study included patients with asthma who were treated with omalizumab or mepolizumab. Eligible patients had a blood eosinophil count ≥ 150/µL (or ≥ 300/µL within the prior year), total Immunoglobulin E (IgE) ≥ 30 IU/mL, and sensitization to a perennial inhalant allergen. The primary endpoint was the adjusted incidence rate ratios (IRRs) for asthma exacerbation during the first year of treatment. Secondary endpoints were IRRs for emergency room (ER) visits and hospitalizations, subgroup IRRs stratified by eosinophil count (< 300/µL vs ≥ 300/µL), and change in oral corticosteroid (OCS) dose. Poisson regression models were adjusted for BMI, eosinophil count, and prior-year exacerbations; ER and hospitalization models additionally adjusted for prior ER visits and hospitalizations. Follow-up time was accounted for via an offset term. Results We included 49 patients (omalizumab, n = 25; mepolizumab, n = 24). Mepolizumab significantly reduced asthma exacerbations compared with omalizumab (IRR, 0.37; 95% confidence interval [CI], 0.19–0.69). In the subgroup analyses, this effect was significant in patients with eosinophil counts < 300/µL (IRR, 0.38; 95% CI, 0.14–0.88) but not in those with eosinophil counts ≥ 300/µL (IRR, 0.47; 95% CI, 0.15–1.35). There were no significant between-group differences in the number of ER visits or hospitalizations. The OCS dose was reduced in both groups, with no significant between-group difference in the mean dose reduction. Conclusions In patients eligible for both therapies, mepolizumab reduced clinically significant exacerbations more than omalizumab in real-world practice. Although ER visits, hospitalizations, and OCS-sparing were comparable, these findings support an exacerbation-focused approach when selecting biologics for overlap-eligible severe asthma. Confirmation in larger multicenter cohorts is warranted.