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Metformin doesn’t help HbA1c in teens with type 1 diabetes

Study fails to support prescribing metformin for glycaemic control in overweight adolescents

Louise Prime

Wednesday, 02 December 2015

Adding metformin to insulin for six months does not improve glycaemic control in teenagers with type 1 diabetes who are overweight, research has shown. Authors of the study*, published online in JAMA this week, said their results did not support the practice of prescribing metformin for these adolescents in an effort to improve glycaemic control.

Being overweight or obese has the potential for serious metabolic consequences, especially during adolescence, for young people with type 1 diabetes; and in this particular group, the high doses of insulin required to overcome the insulin resistance of obesity and puberty contribute to difficulties in glycaemic control and may promote further weight gain.

Earlier studies that looked at whether metformin might improve glycaemic control in adolescents with type 1 diabetes have had inconclusive results, so researchers in the US conducted a randomised controlled trial to find out. This involved 26 paediatric endocrinology clinics, and 140 overweight and obese adolescents aged 12-19 years who had had type 1 diabetes for an average of 7 years. In addition to insulin, 71 were randomised to receive metformin (up to 2,000mg a day) and the other 69 to placebo, for 6 months.

The researchers reported a small decrease in glycated haemoglobin (HbA1C) at 13 weeks in the metformin group compared with the placebo group. But by 26 weeks, mean HbA1c levels had risen in both groups by 0.2% from their baseline level of 8.8%. There were no statistically or clinically significant differences between the groups from baseline to 26 weeks in continuous glucose monitoring. The authors said they believed it unlikely that a longer treatment period would have achieved different glycaemic results.

Compared with the placebo group, the metformin group experienced reductions in weight gain, body mass index, body fat, and total daily insulin dose – although the authors said the clinical relevance of these differences was uncertain. Furthermore, metformin was not associated with improvements in other important clinical and biochemical risk factors for cardiovascular disease, including blood pressure and blood lipids; and its use was associated with a 36% higher number of reports of gastrointestinal adverse events compared with placebo.

The study authors said: “Among overweight adolescents with type 1 diabetes, the addition of metformin to insulin did not improve glycaemic control after 6 months. … [and] resulted in an increased risk for gastrointestinal adverse events. These results do not support prescribing metformin to overweight adolescents with type 1 diabetes to improve glycaemic control.”


* Libman IM, Miller KM, DiMeglio LA et al. Effect of metformin added to insulin on glycemic control among overweight/obese adolescents with type 1 diabetes. JAMA. 2015;314(21):2241-2250. doi:10.1001/jama.2015.16174.

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