LAUSR

To the Editor, Patients with severe eosinophilic asthma experience frequent exacerbations and may require oral corticosteroids (OCS) to maintain asthma control. In randomized controlled trials (RCTs), the anti‐interleukin‐5 monoclonal antibody, mepolizumab, reduces exacerbation rates and OCS use in patients with severe eosinophilic asthma versus placebo. However, due to strict eligibility criteria, RCT populations often have more homogeneous demographics and clinical characteristics than patients treated in real‐world clinical practice. As such, it is important to validate and complement the results of RCTs with effectiveness data from real‐world settings, which can provide valuable information for clinical decision‐making; these data are currently limited for Japan. The objective of the current study was to evaluate the effectiveness of mepolizumab in reducing exacerbations and OCS use in patients with severe asthma in Japan. This was a retrospective, observational, self‐controlled study (GSK ID: 213221) of patients from the Japanese Medical Data Center Claims Database (JMDC Inc., Tokyo, Japan) initiating mepolizumab. The date of the first mepolizumab administration was the index date, and the data were gathered for the 12 months prior to index (baseline period) and up to 12 months following the index date (follow‐up period). Eligible patients for the overall population were ≥12 years of age at index with a diagnosis of asthma during the baseline period and a claim for mepolizumab between June 1, 2016 and August 31, 2018. Additionally, patients had continuous enrollment for the 12 months pre‐ and post‐index. A subgroup analysis of the overall population, which included patients with ≥2 exacerbations during the baseline period and ≥10 mepolizumab administrations during follow‐up, was also performed to assess outcomes in patients with similar characteristics to those in the mepolizumab RCTs. Outcomes were compared annually/quarterly during baseline and follow‐up and included the annual rate and proportion of patients experiencing an asthma exacerbation (all exacerbations and those requiring hospitalization), the proportion of patients receiving maintenance OCS at baseline (≥5 prednisone‐equivalent mg/day OCS with <15‐day gap at the time of mepolizumab initiation for ≥3months before index) who discontinued maintenance OCS during follow‐up, changes inmedian dailyOCSdose frommepolizumab initiation (for the 3months before index date) in patients receiving maintenance OCS at baseline, and the proportion of patients achieving a ≥50% reduction frombaseline in dailyOCSdose in patients receivingmaintenanceOCS at baseline. Other outcomes included the number of mepolizumab administrations and discontinuations during follow‐up. Asthma exacerbations were defined as an asthma outpatient claim and ≥1 prescription for a short course (1–27 days) of systemic corticosteroids (SCS) or an asthma hospitalization with SCS, intravenous aminophylline, or adrenaline recorded during the inpatient stay. For patients currently receiving maintenance therapy (continuous OCS use for ≥180 days with <30 consecutive days gap), asthma exacerbations were defined as requiring an OCS prescription with a mean daily dose at least twice the prior prescription or treatment with intramuscular, or intravenous SCS. Within the overall population, on‐treatment and on/off‐treatment analyses were performed. For on‐treatment analyses, follow‐up was ended upon mepolizumab discontinuation (>90 days without another mepolizumab injection) or at the first instance of any of the following: 1‐year post‐mepolizumab initiation; claim for another asthma biologic (benralizumab, omalizumab, or dupilumab); or 3 days prior to first bronchial thermoplasty. For on/off‐treatment analyses and the subgroup analysis, mepolizumab discontinuation and reinitiation was permitted, and follow‐up was ended at 1‐year post‐mepolizumab initiation, claim for another asthma biologic, or 3 days prior to first bronchial thermoplasty. Exacerbations per patient‐year during the baseline and follow‐up periods were compared using a generalized estimating equation model with assumed Poisson distributions. Median daily OCS dose was calculated by dividing the total prednisone‐equivalent dose for all days in the quarter‐year by the total number of days for the quarter‐year. Although data from both clinical trial and real‐world settings show that mepolizumab improves lung function in patients with severe eosinophilic asthma, the database used in this study does not include lung function parameters. In total, 61 patients were included in the on‐treatment and on/ off‐treatment analyses (two patients in the on‐treatment analysis and two in the on/off treatment analysis discontinued due to first