Reduction in asthma exacerbation rate after mepolizumab treatment initiation in patients with severe asthma: A real-world database study in Japan

Objective To investigate the changes in asthma exacerbation, as well as in oral corticosteroid (OCS) use, exacerbation-related healthcare resource utilization (HRU), and healthcare costs before and after mepolizumab treatment initiation in patients with severe asthma who started treatment with mepolizumab in a real-world clinical setting in Japan. Methods A retrospective, observational, self-controlled study was conducted in Japan using a hospital-based administrative claims database. Patients who were diagnosed with asthma and who were new users of mepolizumab were included in the study. The primary outcome was the incidence rate of any asthma exacerbation/patient-year during the 12-month period before (baseline period) and after (follow-up period) the first mepolizumab prescription. Secondary outcome measures included the proportion of patients with ≥1 any asthma exacerbation, patients with exacerbation requiring hospitalization, the incidence rate of exacerbations requiring hospitalization/patient-year, the median daily OCS dose (OCS sparing effect), exacerbation-related HRU (hospitalization length, the proportion of patients with emergency visits, and the number of emergency/outpatient visits), and associated costs. Results Of the 377 patients included, 56.2% were ≥65 years of age. Following the first mepolizumab prescription, incidence rates for any asthma exacerbation were reduced by 40.6% (4.00/patient-year to 2.38/patient-year; the incidence rate ratio [95% confidence interval]: 0.60 [0.53–0.67]; p < 0.0001) from the baseline to follow-up periods. The incidence rate of exacerbations requiring hospitalization was reduced by 55.8% (0.37/patient-year to 0.16/patient-year) from the baseline to follow-up periods. The proportion of patients experiencing any exacerbation decreased from 84.4% to 57.8% and those requiring hospitalization decreased from 23.9% to 10.3% both from the baseline to follow-up periods. The median daily OCS dose decreased by 44.6% (median [interquartile range]: 6.7 [4.7–9.9] mg/day to 3.3 [0.9–5.6] mg/day) from the last baseline quarter to the 4th quarter of the follow-up period. All exacerbation-related HRUs decreased from the baseline to follow-up periods. Inpatient cost reduced by >50% (123,279 Japanese Yen [JPY]/patient-year vs. 57,283 JPY/patient-year), reducing the total cost by 80,716 JPY from the baseline to follow-up periods. Conclusion Mepolizumab was effective in treating patients with severe asthma by reducing the incidence rates of exacerbations and exacerbation requiring hospitalization, OCS dose, exacerbation-related HRU, and cost in routine clinical practice in Japan.