Metformin use is associated with a decrease in the risk of hospitalization and mortality in COVID-19 patients with diabetes: A population-based study in Lombardy

Aim: To compare the association of metformin use and coronavirus disease 2019 (COVID-19) outcomes in a cohort of 31 966 patients with diabetes in Lombardy. Methods: We used a COVID-19 linkable administrative regional database to select patients with diabetes who were aged 40 years or older. They had at least two prescriptions of antidiabetic drugs in 2019 and a positive test for severe acute respiratory syndrome coronavirus-2 from 15 February 2020 to 15 March 2021. The association of metformin use and clinical outcomes was assessed by multivariable logistic regression analyses and after propensity score matching (PSM). Clinical outcomes were all-cause mortality, in-hospital mortality, hospitalization for COVID-19, and admission to an intensive care unit (ICU). Results: In multivariable models, metformin use was associated with a significantly lower risk of total mortality (OR 0.70; 95% CI 0.66-0.75), in-hospital mortality (OR 0.68; 95% CI 0.63-0.73), hospitalization for COVID-19 (OR 0.86; 95% CI 0.81-0.91), and ICU admission (OR 0.81; 95% CI 0.69-0.94) compared with metformin non-users. Results were similar after PSM; metformin was associated with a significantly lower risk of total mortality (OR 0.79; 95% CI 0.73-0.86), in-hospital mortality (OR 0.74; 95% CI 0.67-0.81), and ICU admission (OR 0.77; 95% CI 0.63-0.95). Conclusions: In this large cohort, metformin use was associated with a protective effect in COVID-19 clinical outcomes, suggesting that it might be a potentially useful drug to prevent severe COVID-19 disease, although randomized controlled trials (RCTs) are needed to confirm this. While awaiting the results of RCTs, we suggest continuing prescribing metformin to COVID-19 patients with diabetes.