Does Metformin Decrease Mortality in Patients with Type 2 Diabetes Mellitus Hospitalized for COVID-19? A Multivariable and Propensity Score-adjusted Meta-analysis

AimsCoronavirus disease 2019 (COVID-19) is a new pandemic that the entire world is facing since December of 2019. Increasing evidence has shown that metformin is linked to favorable outcomes in patients with COVID-19. The aim of this study was to address whether outpatient or inpatient metformin therapy offers low in-hospital mortality in patients with type 2 diabetes mellitus hospitalized for COVID-19. MethodsWe searched studies published in PubMed, Embase, Google Scholar and Cochrane Library up to October 1, 2021. Raw event data extracted from individual study were pooled using the Mantel-Haenszel approach. Odds ratio (OR) or hazard ratio (HR) adjusted for covariates that potentially confound the association using multivariable regression or propensity score matching was pooled by the inverse-variance method. Random effect models were applied for meta-analysis due to variation among studies. ResultsNineteen retrospective observational studies were selected. The pooled unadjusted OR for outpatient metformin therapy and in-hospital mortality was 0.54 (95% CI, 0.42-0.68), whereas the pooled OR adjusted with multivariable regression or propensity score matching was 0.72 (95% CI, 0.47-1.12). The pooled unadjusted OR for inpatient metformin therapy and in-hospital mortality was 0.19 (95% CI, 0.10-0.36), whereas the pooled adjusted HR was 1.10 (95% CI, 0.38-3.15). ConclusionsOur results suggest that there is a significant reduction of in-hospital mortality with metformin therapy in patients with type 2 diabetes mellitus hospitalized for COVID-19 in the unadjusted analysis, but this mortality benefit does not retain after adjustments for confounding bias.