The effect of metformin on blood glucose control in overweight patients with Type 1 diabetes

Aims  In a randomized, double‐blind, cross‐over study, we investigated the effect of metformin on blood glucose control and daily insulin dose in overweight patients with Type 1 diabetes. Methods  We studied 15 C‐peptide‐negative patients, aged 48 ± 12 years, with a body mass index of 31.3 ± 2.6 kg/m 2 . Each patient had a ‘screening visit’, followed by a 4‐week ‘run‐in’ period. This was followed by two separate 16‐week ‘study’ (treatment) periods, separated by a 4‐week ‘wash‐out’ period. Patients received either metformin or placebo during the ‘study’ periods, in random order. Results  HbA 1c was significantly lower following 16 weeks of treatment with metformin (7.8 ± 1.1%) compared with baseline (8.5 ± 1.4%; P  < 0.005) and placebo (8.6 ± 1.2%; P  < 0.005). Fasting plasma glucose, following 16 weeks of metformin treatment, was significantly lower (8.3 ± 2.8 mmol/l) compared with baseline (12.4 ± 3.0 mmol/l; P  < 0.01) and placebo (12.6 ± 3.4 mmol/l; P  < 0.01). Compared with baseline (60 ± 14 units), total daily insulin dose was significantly lower following the addition of metformin (50 ± 13 units; P  < 0.05) and this final total daily insulin dose in the metformin group was lower compared with placebo (58 ± 12 units, P  < 0.05). Body weight did not change following metformin or placebo treatment. Conclusion  Metformin can effectively improve glycaemic control and reduce the total daily insulin dose in overweight people with Type 1 diabetes.