Metformin
Elizabeth Briand
Metformin—one of the most frequently prescribed medications on the planet—is considered the first-line treatment for T2D with an estimated 20 million individuals taking it each day in the United States alone.
For the patients benefiting from this medication, it can be difficult to imagine a scenario in which they would stop their treatment. For individuals who are hospitalized, however, their care teams may halt metformin to help lower the risk of lactic acidosis.
A study published on February 3, 2025, in the Journal of General Internal Medicine looked at this common practice and found that actually continuing the use of metformin during hospital stays might produce better outcomes for patients, helping improve glucose control, lower insulin requirements, and subsequently reduce the risk of hypoglycemia.
“An earlier drug in the same family, phenformin, had high risk of lactic acidosis, and so it was thought that metformin may have the same risk,” said Robert Gallo, MD, one of the study’s authors and medical informatics research fellow at the VA Palo Alto Health Care System.
Because of that, guidelines have generally recommended that clinicians hold metformin during hospitalizations in case of clinical instability. Subsequent studies, though, “have found low risk of lactic acidosis for metformin, outside of other causes of lactic acidosis—sepsis, heart failure exacerbations, hypoperfusion—or renal insufficiency,” said Gallo.
Alternative approach
The study included adults with T2D who had been admitted to a Veterans Health Administration hospital for common medical conditions from 2016 through 2022. Researchers examined more than 67,000 hospitalizations and the cohort was split evenly between those who continued metformin during the hospital stays and those who did not. The study’s authors noted that continuation of metformin varied widely depending on the institution, indicating that much of the decision making was a matter of local practice.
Results of the study showed that within 90 days of hospital discharge, the risk of hypoglycemia was lower for those individuals who continued to receive their metformin. Readmissions and mortality rates were also lower.
“Continuation of metformin during hospitalization can help maintain steady glucose levels, reducing the need for insulin,” said Gallo. “Decreased inpatient insulin requirements likely lead to decreased prescriptions at discharge and associated decreased risk of hypoglycemia.”
The study showed that patients whose metformin was discontinued during their hospitalizations were potentially vulnerable to issues such as hypoglycemia.
“Once the metformin that was held during hospitalization is restarted after discharge, the patient’s insulin requirements decrease,” said Gallo. “This can put patients at risk of hypoglycemia in the outpatient setting where their glucose may not be as closely monitored.”
Withholding metformin for inpatients appeared to result in an increase in insulin prescriptions for patients, too.
“Since holding metformin during the hospital stay leads to higher blood glucose, these patients may be more likely to require insulin and at higher doses,” Gallo said. “This in turn probably leads to increased insulin prescriptions at discharge, with the assumption that the patient will require insulin for glucose control given their insulin requirements during the hospital stay.”
Metformin should continue to be held during hospitalization for individuals with significant renal impairment, lactic acidosis, or hemodynamic instability, said the authors.
Pharmacist support
“Pharmacists can help remind the medical team that holding metformin during hospital admission will increase the patient’s insulin requirements, which is especially important for discharge planning,” Gallo said.
“Insulin requirements may change around the transition from the hospital to home, especially with changes in medications,” Gallo said. ■