Prevalence and Predictors of Metformin Prescribing in Adults with Type 2 Diabetes Mellitus: A National Cross-Sectional Study

OBJECTIVE Metformin is the first-line oral type 2 diabetes treatment. Despite an abundance of evidence, metformin is routinely underused. This study evaluated the rates of metformin use in an appropriate outpatient type 2 diabetes population and identified predictors of metformin use. METHODS A national cross-sectional study was conducted using data from the National Ambulatory Medical Care Survey. Office visits involving patients aged 18-79 years with a diagnosis of type 2 diabetes were included, and visits involving patients with a diagnosis of chronic renal failure or heart failure were excluded. The primary outcome was metformin-prescribing rate. Multivariate logistic regression identified variables associated with metformin prescribing. RESULTS A total of 2348 patient visits were eligible for inclusion, representing 88,671,714 office visits nationally. Metformin was continued or initiated in 40.6% of these visits. The strongest independent predictors of metformin prescribing were insulin use (odds ratio [OR] 0.32; 95% confidence interval [CI] 0.21-0.47), presence of four or more chronic conditions (OR 0.58; 95% CI 0.34-0.98), patients with Medicare insurance (OR 0.57; 95% CI 0.39-0.83), visit with a surgical specialist (OR 0.39; 95% CI 0.25-0.61) or a medical specialist (OR 0.59; 95% CI 0.38-0.92), and Hispanic ethnicity (OR 2.03; 95% CI 1.28-3.22). CONCLUSION Metformin-prescribing rates are low, particularly in patients receiving insulin, with Medicare insurance, seen by medical or surgical specialists, or with four or more chronic conditions. The observed low rates of metformin use represent an important opportunity to improve the quality of care for patients with type 2 diabetes.