• Robert J Gallo, Shoutzu Lin, Daniel Z Fang, Peter A Glassman, Anju Sahay, and Paul A Heidenreich.
• Center for Innovation to Implementation, VA Palo Alto Health Care System, 795 Willow Rd (152-MPD), Menlo Park, CA, 94025, USA. rjgallo@stanford.edu.
• J Gen Intern Med. 2025 Feb 3.

BackgroundMetformin is the first-line treatment for diabetes, with multiple long-term benefits. However, there is limited evidence for its use in the inpatient setting, and clinical guidelines have historically recommended holding oral diabetes medications during acute hospitalization. While studies have not found evidence of harm from continuing metformin during hospitalization, withholding may lead to unnecessary insulin prescriptions, which in turn may lead to hypoglycemia events after discharge and other associated complications.ObjectiveTo investigate the association between metformin use during hospitalization and post-hospitalization outcomes.DesignObservational cohort study from January 2016 to January 2022, emulating a target trial.ParticipantsAdults with type 2 diabetes admitted to a Veterans Health Administration hospital for common medical conditions.InterventionsContinuation of an outpatient metformin prescription during hospitalization.Main MeasuresHypoglycemia within 90 days of discharge. Secondary outcomes included insulin prescriptions at discharge, 90-day readmissions, and 90-day mortality.Key ResultsThe propensity-matched cohort included 67,162 hospitalizations, equally split between those who did and did not have metformin continued during hospitalization. Within 90 days of hospital discharge, those that received metformin had lower risk of hypoglycemia (1.5% vs 1.8%; OR 0.83, 95% CI 0.73-0.93; p = 0.003), readmissions (29.4% vs 30.6%; OR 0.96, 95% CI 0.92-1.00; p= 0.03), and mortality (6.4% vs 7.4%; OR 0.86, 95% CI 0.80-0.92; p <0.001). Patients receiving metformin also had lower risk of insulin prescriptions at discharge (18.5% vs 20.3%; OR 0.89, 95% CI 0.84-0.95; p<0.001).ConclusionsContinuation of metformin during hospitalization for patients with type 2 diabetes was associated with decreased risk of post-hospitalization insulin prescriptions and 90-day hypoglycemia, readmissions, and mortality. These findings question clinical guideline recommendations to hold metformin during hospitalization.© 2025. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.

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