Metformin treatment should be maintained in non-obese type-2 diabetes patients who are started on insulin, Scandinavian research suggests.

The study showed that both metformin and the insulin secretagogue repaglinide were safe and effective when combined with insulin treatment in this patient group.

Both combinations provided good glycaemic control and were associated with an equal risk of hypoglycaemia in this one-year trial. However, metformin performed better than repaglinide in being associated with lower weight gain.

The study included 101 type-2 diabetes patients with a BMI of 27 or lower. At the start of the study, all patients had an HbA1c of at least 6.5 per cent, despite taking oral hypoglycaemic agents, or an HbA1c of greater than 9.5 per cent despite taking insulin therapy.

Patients were treated with a combination of metformin 1,000mg twice daily or repaglinide 2mg three times daily, plus injections of insulin aspart 70/30.

After 12 months' treatment, both groups achieved good glycaemic control, with an average HbA1c of less than 7 per cent.

There was no difference between the groups in total daily insulin dose or in rate of adverse events.

However, there was a significant difference between the groups in weight gain. Metformin patients gained an average of 2.22kg compared with 4.73kg gained by those taking repaglinide.

Lead researcher Dr Allan Vaag, chief physician in the department of endocrinology at the University of Lund, in Malmo, Sweden, said that this was the first evidence supporting the use of metformin plus insulin in non-obese patients with type-2 diabetes.

'Other studies have shown that it is beneficial to combine metformin and insulin in obese patients with type-2 diabetes, but there are very little data on non-obese patients.

'We found that metformin was also the drug of choice for combining with insulin in non-obese patients with type-2 diabetes.'

• BMJ Online 2009