OBJECTIVES : Metformin is the recommended first-line pharmacotherapy for type 2 diabetes. The recommended initial metformin dose is 500-1,000 mg daily, with recommended increases of 500 mg weekly/850 mg biweekly. The minimum effective dose of metformin has been reported as 1,500 mg daily. This study examined metformin dosage patterns at initiation and at three months in patients at an integrated healthcare system in the US.

METHODS : A retrospective cohort study of adults with type 2 diabetes receiving an initial metformin prescription during 2012-2016 was conducted using electronic medical records. Proportion of patients receiving different initial metformin doses and proportion of patients receiving ≥ 1,500 mg metformin daily within three months of initiation and the associated patient characteristics were examined. Statistical tests included chi-square test, Student’s t-test, and logistic regression.

RESULTS : The cohort included 5,308 patients, 53.4% male and 69.1% Caucasian, with a mean age of 55.8 (±12.1) years. Of these, 79.1% received an initial daily metformin dose of ≤ 1,000 mg, 3% received 1,500/1,700 mg, and 19.2% received ≥ 2,000 mg. A total of 1,707 (32.2%) patients received ≥ 1,500 mg metformin daily within three months of initiation. Patients aged ≥ 80 years (adjusted odds ratio [AOR] = 0.34, 95% confidence interval [CI] = 0.20-0.59) (vs. patients aged < 50 years), blacks (AOR = 0.73, 95% CI = 0.63-0.85) (vs. whites), and patients with higher Elixhauser comorbidity index (AOR = 0.93, 95% CI = 0.89-0.98) were less likely whereas patients with higher HbA1c before metformin initiation (AOR = 1.09, 95% CI = 1.05-1.12) were more likely to receive ≥ 1,500 mg metformin daily within three months of initiation.

CONCLUSIONS : Study findings suggest the need of interventions to maximize the proportion of patients receiving a recommended metformin dose. Factors impacting metformin dosage identified in the study could guide planning of these interventions.