Long-term Efficacy and Safety of Mepolizumab in Patients With Severe Eosinophilic Asthma: A Multi-center, Open-label, Phase IIIb Study

Purpose: Patients with severe eosinophilic asthma often experience recurrent asthma exacerbations despite intensive inhaled corticosteroid therapy. In 2 previous double-blind studies (MENSA [NCT01691521] and SIRIUS [NCT01691508]), treatment with intravenous or subcutaneous mepolizumab was associated with significantly reduced annualized exacerbation rates and oral corticosteroid (OCS) requirements compared with placebo. The purpose of this study was to assess the long-term safety and efficacy of subcutaneous mepolizumab treatment in patients with severe eosinophilic asthma.

Methods: COSMOS was a 52-week, open-label extension study in patients who received mepolizumab or placebo in MENSA or SIRIUS. Patients received subcutaneous mepolizumab regardless of prior treatment allocation and continued to receive appropriate standard-of-care asthma therapy throughout. The primary objective was to assess the long-term safety of mepolizumab; end points included adverse events (AEs) and serious AEs (SAEs). Efficacy assessments included the annualized exacerbation rate and durability of response (defined as the exacerbation rate and OCS dose reduction when combined with MENSA and SIRIUS data, respectively).

Findings: In total, 558 (86%; previous mepolizumab: 358; previous placebo: 200) and 94 (14%; previous mepolizumab: 58, previous placebo: 36) patients experienced on-treatment AEs and SAEs, respectively. No fatal AEs were reported. Totals of 13 (2%) and 29 (4%) patients experienced systemic and local site reactions, respectively. There were no reports of mepolizumab-related anaphylaxis. Mepolizumab treatment was shown to exert a durable response, with patients who previously received mepolizumab in MENSA or SIRIUS maintaining reductions in exacerbation rate and OCS dosing throughout COSMOS. Patients who previously received placebo in MENSA or SIRIUS demonstrated improvements in these end points following treatment with mepolizumab in COSMOS.

Implications: These data demonstrate a favorable safety profile of mepolizumab and indicate a durable and stable effect over time, supporting long-term treatment in patients with severe eosinophilic asthma. ClinicalTrials.gov identifier: NCT01842607.