Association between continued metformin use during hospital admission and hospital-acquired complications

Aims: The safety of continuing metformin during a hospital admission has not been robustly demonstrated. We evaluated the association of continuing metformin in hospital with the risk for a hospital-acquired complication (HAC). Methods: This is a retrospective observational study of patients admitted to a medical or surgical ward. We considered those with diabetes who continued metformin (DM/MET group), those who discontinued metformin upon admission (DM/MET-STOP), and those with diabetes not on metformin just prior to and during admission (DM/NoMET). We prepared propensity score-matched (PSM) control groups from admitted patients without diabetes. The likelihood of a HAC was determined using a Kaplan–Meier survival analysis. A Cox proportional hazards model was employed to calculate the hazard ratio, adjusted for covariates. Results: Of the 4446 (14%) patients with diabetes, 3331 (10%) were prescribed metformin on admission, and it was continued in 2557 patients. HAC occurred in 5.5% of DM/MET group and 6.4% of the PSM control group. Continuation of metformin was associated with a lower likelihood of HAC, adjusted hazard ratio 0.85 (95% CI 0.69, 1.04), p = 0.117 compared to a PSM-matched control group without diabetes. The DM/NoMET and DM/MET-STOP groups had an increased risk for HAC, adjusted HR 1.77 (1.44, 2.18), p < 0.001 and 2.57 (2.10, 3.13), p < 0.001, as compared to their respective PSM control groups. Conclusion: An individualized assessment to continue metformin during hospital admission was associated with a reduced likelihood of HAC, with the caveat that there was limited matching to non-diabetes controls. This finding warrants further exploration.