The 2023 American Diabetes Association (ADA) Standards of Care in Diabetes guideline discusses recommendations for diabetes care for hospitalized patients, but mainly focuses on insulin therapy. In a non-critical care setting, insulin is mentioned to be the preferred treatment for hyperglycemia in hospitalized patients, though it is noted that oral glucose-lowering medications may be continued under certain conditions. Unfortunately, no guidance was provided for or against metformin use in the inpatient setting; however, when discussing perioperative care, the guidelines recommend that metformin should be held on the day of surgery. [1]
The 2019 Joint British Diabetes Societies document for the management of diabetes in inpatient settings summarizes previous guideline recommendations on metformin use, separated by patient populations. For breastfeeding patients, metformin may be taken after birth, and other oral anti-diabetic treatments should be avoided. For patients on maintenance hemodialysis, metformin should be avoided. For stroke patients who require enteral feeding, resuspended metformin powder may be considered for mild hyperglycemia over other oral hypoglycemic medications (e.g., sulphonylureas). There is a lack of guidance in the document for use of metformin overall in hospitalized patients. [2]
A 2022 study reviewed the evidence for the inpatient management of hyperglycemia in non-critically ill patients with type 2 diabetes, focusing on non-insulin treatments. With regards to metformin, its use has not been recommended in the hospital setting by clinical guidelines due to the risk for lactic acidosis and other side effects; however, a number of retrospective studies have shown no increased risk of adverse events. Additionally, it is common practice to hold metformin in patients undergoing radiological studies with administration of intravenous contrast for 72 hours from the start of the procedure (i.e., percutaneous coronary intervention [PCI]); again several observational studies have reported a low risk of lactic acidosis attributed to metformin after radiological procedures or PCI, especially in patients with glomerular filtration rate > 30-60 mL/min/1.73 m2. In patients at risk for lactic acidosis (i.e., patients with renal failure, sepsis, hypoxia, liver failure, and alcoholism), metformin is not recommended to be used. Overall, there is a lack of evidence to support the use of metformin in the hospital setting; the authors concluded that if patients are relatively stable, without renal impairment, and not at increased risk for lactic acidosis, then continuation of metformin may be safe. [3]
Additionally, a recently published meta-analysis examined metformin therapy in patients hospitalized for COVID-19 to determine whether an association existed between therapy and the reduction of in-hospital mortality. A pooled analysis of 5 studies appears to link inpatient metformin use with a significant reduction of in-hospital death (unadjusted odds ratio [OR] 0.18; 95% confidence interval [CI] 0.1 to 0.31; I2= 0%). However, an adjusted analysis looking at the hazard ratio [HR] of 2 studies suggested no statistically significant association between in-hospital mortality and inpatient metformin use (HR 1.1; 95% CI 0.38 to 3.15; I2= 43%). The authors note that although there is mounting evidence to suggest that using metformin to treat diabetic patients with COVID-19 is not harmful, it does not appear to endow a protective effect, either. [4]