Association of metformin with susceptibility to COVID-19 in people with Type 2 diabetes.

Objective Diabetes has emerged as an important risk factor for mortality from COVID-19. Metformin, the most commonly prescribed glucose-lowering agent, has been proposed to influence susceptibility to and outcomes of COVID-19 via multiple mechanisms. We investigated whether, in patients with diabetes, metformin is associated with susceptibility to COVID-19 and its outcomes. Research design and methods We performed a propensity score-matched cohort study with active comparators using a large UK primary care dataset. Adults with type 2 diabetes patients and a current prescription for metformin and other glucose lowering agents (MF+) were compared to those with a current prescription for glucose-lowering agents that did not include metformin (MF-). Outcomes were confirmed COVID-19, suspected/confirmed COVID-19, and associated mortality. A negative control outcome analysis (back pain) was also performed. Results There were 29,558 and 10,271 patients in the MF+ and MF- groups respectively who met the inclusion criteria. In the propensity score-matched analysis, the adjusted hazard ratio for suspected/confirmed COVID-19, confirmed COVID-19, and COVID-19 related mortality were 0.85 (95%CI 0.67, 1.08), 0.80 (95%CI 0.49, 1.30), and 0.87 (95%CI 0.34, 2.20) respectively. The negative outcome control analysis did not suggest unobserved confounding. Conclusion Current prescription of metformin was not associated with the risk of COVID-19 or COVID-19 related mortality. It is safe to continue prescribing metformin to improve glycaemic control in patients with diabetes, despite concerns about an impending second wave of COVID-19.