If metformin does reduce COVID-19 deaths, multiple mechanisms likely
In his article, Dr. Scheen noted that several mechanisms have been proposed for the possible beneficial effect of metformin on COVID-19 outcomes, including direct improvements in glucose control, body weight, and insulin resistance
He noted that some authors have raised concerns about possible harms from the use of metformin by patients with type 2 diabetes who are hospitalized for COVID-19, particularly because of the potential risk for lactic acidosis in cases of multiple organ failure. Taken together, the four observational studies that Dr. Scheen reviewed showed that metformin had a positive effect, with an overall 25% reduction in death (P < .00001), albeit with relatively high heterogeneity (I² = 61%). The largest of these, from the United States, included 6,256 patients hospitalized with COVID-19 and involved propensity matching. A significant reduction in mortality with metformin use was seen in women but not men (odds ratio, 0.759). The French Coronavirus-SARS-CoV-2 and Diabetes Outcomes (CORONADO) study of 1,317 patients with diabetes and confirmed COVID-19 who were admitted to 53 French hospitals also showed a significant survival benefit for metformin, although the study wasn’t designed to address that issue. In that study, the odds ratio for death on day 7 in prior metformin users compared to nonusers was 0.59. This finding lost significance but remained a trend after full adjustments (0.80). Two smaller observational studies produced similar trends toward survival benefit with metformin. Nonetheless, Dr. Scheen cautioned: “Firm conclusions about the impact of metformin therapy can only be drawn from double-blind randomized controlled trials (RCTs), and such trials are almost impossible in the context of COVID-19.” He added: “Because metformin is out of patent and very inexpensive, no pharmaceutical company is likely to be interested in planning a study to demonstrate the benefits of metformin on COVID-19-related clinical outcomes.” Dr. Lipska agreed: “RCTs are unlikely to be conducted to settle these issues. In their absence, metformin use should be based on its safety and effectiveness profile.” Dr. Scheen concluded, however, that “there are at least no negative safety indications, so there is no reason to stop metformin therapy during COVID-19 infection except in cases of severe gastrointestinal symptoms, hypoxia and/or multiple organ failure.” Dr. Lipska has received grants from the National Institutes of Health and works under contract for the Centers for Medicare & Medicaid Services to develop publicly reported quality measures. Dr. Scheen has disclosed no relevant financial relationships. A version of this article originally appeared on Medscape.com. *A previous version reversed these two outcomes in error. In totality, four studies suggest 25% death reduction with metformin
