A systematic review 1 including 19 studies was abstracted in DARE.
The weighted mean difference (WMD) between metformin and placebo after treatment for fasting blood glucose was -2.0 mmol/l (95% CI: -2.4 to -1.7) and for glycosylated haemoglobin -0.9% (95% CI: -1.1 to -0.7). Body weight WMD was not significant after treatment. Sulfonylurea and metformin lowered glycosylated haemoglobin and blood glucose equally, while there was a significant WMD in body weight (-2.9 kg (95% CI: -4.4 to1.1)) because of a 1.7 kg mean increase after sulfonylurea and a 1.2 kg decrease after metformin.
Another systematic review 2 including 11 RCTs with a total of 651 subjects was abstracted in DARE. There was a 14% reduction in fasting plasma glucose with metformin and a 19% fall in the sulfonylurea group. There was a similar 44.5% reduction in the postprandial glucose level with both groups of drugs. Both the metformin and sulfonylurea treatments resulted in a reduction of glycated haemoglobin of 1.25% (a 12.5% fall). Overall there was a 4 kg weight differential (-1.2 kg vs +2.8 kg) in favour of the metformin-treated patients.
A fourth systematic review 3 including 5 studies with a total of 5,408 subjects comparing metformin to other therapies was abstracted in DARE. Metformin was found to be as effective as sulphonylureas and had a more prominent postprandial effect than sulphonylureas or insulin. When combined with sulphonylurea, metformin exerts antihypeglycaemic effects above those provided by the sulphonylurea. Adverse effects include reduced absorption of vitamin B12 and folic acid, as well as gastrointestinal reactions (diarrhoea, nausea, abdominal pain and metallic taste).
Comment: The review was of poor quality.
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