Exacerbations of severe asthma in patients treated with mepolizumab

Mepolizumab, a humanised monoclonal antibody that neutralises interleukin-5, reduces exacerbations of severe eosinophilic asthma and chronic obstructive pulmonary disease (COPD) [1, 2]. The beneficial effect of treatment is most obvious in patients with a raised peripheral blood eosinophil count, a group who are at high risk of exacerbation off treatment [2, 3]. Even in this population, exacerbation rates whilst receiving mepolizumab are around one per patient per year. The nature of these remaining exacerbations has not been described. We carried out a post hoc comparison of exacerbations occurring during treatment with mepolizumab or placebo in a previously reported, double-blind, placebo-controlled trial of mepolizumab in severe eosinophilic asthma [1]. We tested the hypothesis that exacerbations in each group differ with respect to change in symptom scores, forced expiratory volume in 1 s (FEV1) and inflammatory profile.