Does Metformin Added to Basal Insulin Improve Glycemic Control in Overweight Adolescents With Type 1 Diabetes?

Study Questions:

What is the efficacy and safety of metformin as an adjunct to insulin in treating overweight adolescents with type 1 diabetes?


This was a multicenter, double-blind, placebo-controlled, randomized clinical trial involving 140 adolescents ages 12.2-29.6 years. Participants were randomized to placebo or metformin, titrated to 2000 mg. At baseline, 13 weeks, and 26 weeks, each participant's height, weight, blood pressure, and waist circumference were measured; fasting blood for laboratory measurement was drawn. The primary outcome was change in glycated hemoglobin from baseline to 26 weeks.


A total of 140 participants were enrolled (n = 71 randomized to metformin; n = 69 randomized to placebo). At 13-week follow-up, reduction in glycated hemoglobin was greater with metformin (-0.2%) than placebo (0.1% mean difference, -0.3%; 95% confidence interval [CI], -0.6% to 0.0%). This effect was not sustained at 26-week follow-up. At 26-week follow-up, total daily insulin per kilogram of body weight was reduced by ≥25% from baseline among 23% of participants in the metformin group versus 1% of participants in the placebo group (mean difference, 21%; 95% CI, 11% to 32%; p = 0.003).


The investigators concluded that among overweight adolescents with type 1 diabetes, the addition of metformin to basal insulin did not improve glycemic control after 6 months.


This is an important study predicated on the need to understand best practices in overweight and obese individuals with type 1 diabetes. The data from this analysis would not support the addition of metformin to insulin to improve glycemic control after 6 months. That said, metformin, compared with placebo, was associated with reductions in weight gain. The clinical relevance of this observation needs to be investigated as the obesity epidemic becomes more and more prevalent.

Clinical Topics: Congenital Heart Disease and Pediatric Cardiology, Diabetes and Cardiometabolic Disease, Prevention, CHD and Pediatrics and Arrhythmias, CHD and Pediatrics and Prevention

Keywords: Adolescent, Blood Glucose, Diabetes Mellitus, Hemoglobin A, Glycosylated, Insulin, Metabolic Syndrome X, Metformin, Obesity, Overweight, Primary Prevention, Waist Circumference, Weight Gain

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