Mepolizumab use in cystic fibrosis-associated allergic bronchopulmonary aspergillosis.

Allergic bronchopulmonary aspergillosis (ABPA) is common in cystic fibrosis (CF). Treatment is challenging and the relapse rate is high. Standard therapy is oral steroids and antifungals. However, long-term systemic steroid often results in adverse effects and drug interactions between azoles and CFTR modulators are a potential concern. Mepolizumab, an anti-interleukin (IL)-5 monoclonal antibody, can benefit patients with severe eosinophilic asthma and there are reports of mepolizumab use in ABPA but not in ABPA complicating CF. We present the case of an adult with CF who had recurrent ABPA and intolerable treatment side effects with steroid, azole, and omalizumab. Mepolizumab was well tolerated and led to significantly improved clinical stability and symptomatic improvement. To our knowledge, this is the first report of successful mepolizumab treatment for ABPA in CF. Mepolizumab may be an important adjunctive treatment for difficult to control ABPA in CF.