Association of Metformin Initiation and Risk of Asthma Exacerbation. A Claims-based Cohort Study

Rationale: Diabetes and metabolic syndrome have been associated with worsened asthma control. Metformin improves insulin resistance and metabolic function. Experimental studies suggest that metformin may improve pathologic features of asthma, but evidence of clinical benefit is limited.Objectives: To determine if treatment with metformin in a cohort of individuals with asthma and diabetes is associated with lower risk of asthma exacerbation.Methods: A 6-year retrospective cohort of individuals over age 18 with asthma and diabetes was assembled from a national administrative claims database. New users of metformin were matched to nonusers by propensity score on the basis of demographic, comorbidity, and medication-use characteristics. An exacerbation was defined as an asthma-related hospitalization, emergency department visit, or filling of a systemic corticosteroid prescription within 14 days of an asthma-related ambulatory visit. Cox proportional hazards estimated the change in hazard of asthma exacerbation associated with metformin initiation.Results: In a cohort of 23,920 individuals with asthma and diabetes, metformin initiation was associated with lower hazard of asthma exacerbation (hazard ratio [HR], 0.92; 95% confidence interval [CI], 0.86-0.98), driven by lower hazards of asthma-related emergency department visits (HR, 0.81; 95% CI, 0.74-0.88) and hospitalization (HR, 0.67; 95% CI, 0.50-0.91), without differences in corticosteroid use (HR, 0.96; 95% CI, 0.86-1.03).Conclusions: In an administrative cohort of individuals with asthma and diabetes, metformin initiation was associated with a lower hazard of asthma-related emergency department visits and hospitalizations. These findings suggest a possible benefit of metformin in more severe asthma exacerbations. Investigation within cohorts with more detailed participant characterization is necessary.