Diabetes is associated with worse asthma morbidity. Metformin, which treats diabetes, may have a role among patients with asthma and glycemic dysfunction.
To determine the association between metformin use and asthma exacerbations among patients with diabetes.
We queried the Johns Hopkins EHR from April 1, 2013 to May 31, 2018. Adults with asthma and diabetes were followed from first hemoglobin A1c (HbA1c) test to an asthma-related systemic corticosteroid prescription, emergency department (ED) visit, or hospitalization. Multivariable Cox models estimated time to each outcome associated with metformin use, modeled as either time-invariant (status at HbA1c testing) or time-dependent (based on fill data). Mediation of results by HbA1c was assessed. Sensitivity analysis was performed by propensity score matching.
The cohort comprised of 1,749 adults with asthma and diabetes. Metformin use at entry was associated with a lower hazard of asthma-related ED visits (adjusted hazard ratio [aHR] 0.40, 95% confidence interval [CI] 0.22-0.75) but not steroid prescription (aHR 0.89; 95% CI 0.70-1.13) or hospitalization (aHR 0.38, 95% CI 0.13-1.12). HbA1c did not mediate the association with ED visits. With metformin exposure modeled as time-dependent, metformin use was additionally associated with lower hazard of asthma-related hospitalization (aHR 0.30, 95% CI 0.09-0.93). Results were consistent within a sub-cohort of 698 metformin users matched 1:1 to non-users by propensity score.
Metformin use, independent of glycemic control and obesity, was associated with lower hazard of asthma-related ED visits and hospitalizations. Metformin may have benefit in patients with asthma and glycemic dysfunction.

Copyright © 2021. Published by Elsevier Inc.

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