Usefulness of the addition of metformin to insulin in pediatric patients with type 1 diabetes mellitus

Background: The aim of this study was to evaluate the effect of metformin in addition to insulin therapy in adolescents and young adults with type 1 diabetes mellitus. Methods: Nine patients, two males and seven females, aged 18.1 +/- 3.0 years, with type 1 diabetes mellitus were studied. They were relatively overweight with a body mass index (BMI) of 24.2 +/- 1.8 and had high levels of HbA1c at 9.5 +/- 1.2% despite high doses of insulin of 74.0 +/- 31.2 U/day. Metformin at the dose of 500-750 mg daily was administered to the patients in addition to insulin therapy for 1 year. Results: HbA1c, BMI and insulin dose were compared before 1 year without metformin therapy, at baseline, and at 3, 6 and 12 months during the use of metformin in addition to insulin therapy. HbA1c lowered (8.6 +/- 1.4**, 8.4 +/- 1.3**, 8.4 +/- 1.2*%), BMI was reduced (23.9 +/- 1.7*, 23.8 +/- 1.8, 23.5 +/- 1.8*), and insulin requirement decreased (69.8 +/- 29.7*, 68.7 +/- 29.8**, 67.3 +/- 29.1**U/d) significantly after the start of metformin therapy (*P < 0.05, **P < 0.01 vs at baseline). There were no adverse events, not even lactic acidosis, during the study period. Conclusion: Metformin is safe and may represent a useful adjunct to the management of type 1 diabetes mellitus in adolescents and young adults who have poor glycemic control despite a large amount of insulin.