Six-Month Benralizumab Maintenance for Relapsing Chronic Eosinophilic Pneumonia Guided by Eosinophil Kinetics

Idiopathic chronic eosinophilic pneumonia (ICEP) often relapses upon corticosteroid tapering. Biologics targeting interleukin-5 (IL-5) are effective, but optimal dosing intervals remain unclear. We report a case of relapsing ICEP in a patient in her 50s. Mepolizumab, an IL-5 ligand blocker, failed to maintain remission, with clinical relapse occurring 4 months after initiation. Switching to benralizumab, an interleukin-5 receptor blocker, induced rapid and deep eosinophil depletion. For optimising dosing, treatment was temporarily withheld, revealing a prolonged remission duration of 8 months before eosinophil recovery and clinical relapse. Based on these kinetics, a 6-monthly benralizumab maintenance strategy was established. The patient has remained relapse-free with zero eosinophils for over 2 years under this biannual regimen. This case suggests that benralizumab offers superior durability compared to mepolizumab in CEP due to deep depletion, enabling an extended, cost-effective dosing interval guided by individual eosinophil recovery kinetics.