Background and objective: Metformin is a first-line treatment for patients with diabetes. Recent animal studies indicated that metformin can reduce airway inflammation. However, it remains unclear whether the use of metformin can help patients maintain asthma control. The purpose of this study was to evaluate the association between the use of metformin and asthmarelated outcomes, which include asthma-related hospitalization, asthma-related emergency room visits and asthma exacerbation, among patients with concurrent asthma and diabetes. Methods: We conducted an 11-year (2001-2011) retrospective cohort study using the Taiwan National Health Insurance Research Database. Patients with concurrent asthma and diabetes were included. The date of the first observed prescription of metformin was defined as the index date. For each metformin user, two matched metformin non-users of the same age and gender were randomly selected. Patients were followed for 3 years to measure the occurrence of asthma-related outcomes. Multivariable logistic regression models were used to assess the association between metformin use and asthma-related outcomes. Results: Of 1332 patients with concurrent asthma and diabetes, 444 (33.3%) were metformin users. Compared with non-users, metformin users had a lower risk of asthma-related hospitalization (OR = 0.21, 95% CI: 0.07-0.63) and asthma exacerbation (OR = 0.39, 95% CI: 0.19-0.79). Conclusion: The risk of asthma-related outcomes was lower for metformin users than non-users. Health-care providers should consider metformin as a treatment strategy for patients with concurrent asthma and diabetes.

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