Targeting the IL-5 pathway in eosinophilic asthma: a comparison of mepolizumab to benralizumab in the reduction of peripheral eosinophil counts

BACKGROUND: Mepolizumab and benralizumab are biologics approved for severe eosinophilic asthma. Mepolizumab is an anti-interlukin-5 (IL-5) antibody while benralizumab is an anti-interleukin-5 receptor alpha (IL-5Rα) antibody targeting the IL-5 receptor on eosinophils. Both therapies reduce oral corticosteroid requirements and asthma exacerbations. However, no head-to-head studies have been published. The aim of the present study was to compare the efficacy of peripheral eosinophil reduction of mepolizumab and benralizumab. METHODS: A retrospective chart review was conducted on patients with severe eosinophilic asthma who were approved for either IL-5 agent. Patients with noted non-adherence or those who were on fluctuating doses of corticosteroids for non-asthma related illnesses were excluded. The last detectable eosinophil count for each patient prior to start of therapy was compared to the highest eosinophil count noted after therapy start with at least 30 days of adherence. RESULTS: Thirty-six patients taking mepolizumab and 19 patients taking benralizumab met the inclusion criteria and had both pre-treatment and post-treatment eosinophil counts. Baseline characteristics were not statistically different between those on mepolizumab and benralizumab therapy. The mean pre-therapy serum eosinophil count did not statistically differ between patients on mepolizumab (597.2 cells/µL) compared to benralizumab (521.6 cells/µL), p = 0.3769. While both therapies resulted in a significant decrease in eosinophil count (p < 0.0001); the mean decrease did not statistically differ between patients taking mepolizumab compared to those on benralizumab, p = 0.9079. Nonetheless, 100% of patients receiving benralizumab had undetectable eosinophil counts post-therapy compared to 31% of patients receiving mepolizumab (p < 0.0001). CONCLUSION: Both mepolizumab and benralizumab are potent targets of the IL-5 pathway with the ability to significantly reduce peripheral eosinophil counts. While there is there is no statistical difference in the magnitude of eosinophil reduction offered by each agent, benralizumab is able to decrease peripheral eosinophil counts to 0 cells/µL in more patients than mepolizumab.