Metformin treatment should be continued in type-2 diabetes patients started on insulin, research suggests.
Continuing treatment reduces risk of macrovascular complications, but not those of a microvascular nature.
Dr Coen Stehouwer and colleagues from Maastricht University in the Netherlands studied 390 patients with type-2 diabetes. Patients were treated with insulin for 4.3 years and had either metformin or a placebo added to their treatment.
The researchers found that metformin reduced patients' risk of a macrovascular event by 40 per cent. They suggested that this may be partly due to weight loss achieved by the patients.
'These sustained beneficial effects support the policy of continuing metformin treatment after the introduction of insulin in any patient with type-2 diabetes mellitus, unless contraindicated,' the researchers said.
They calculate that 16 patients would need to be treated with metformin to prevent one macrovascular event.
Metformin treatment also led to improved glycaemic control and reduced insulin requirements.
Dr Stehouwer and his colleagues believe that this is the first study to examine the impact of metformin and insulin on vascular risk.
They found that the beneficial effects of metformin on weight and insulin continued to improve during the 4.3 years of treatment. Improvements in glycaemic control occurred rapidly but were not maintained.
The researchers suggest that a reduction in microvascular risk was not seen in this study because such benefits only accrue over a longer period than the four years of this study.
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