Metformin improves glycemic control in poorly controlled type 2 diabetic patients. Its effect in type 2 diabetic patients who are intensively treated with insulin has not been studied. A total of 390 patients whose type 2 diabetes was controlled with insulin therapy completed a randomized controlled double-blind trial with a planned interim analysis after 16 weeks of treatment. The subjects were selected from three outpatient clinics in regional hospitals and were randomly assigned to either the placebo or metformin group, in addition to insulin therapy. Intensive glucose monitoring with immediate insulin adjustments according to strict guidelines was conducted. Indexes of glycemic control, insulin requirements, body weight, blood pressure, plasma lipids, hypoglycemic events, and other adverse events were measured.

The Results from the 390 subjects showed, 37 dropped out (12 in the placebo and 25 in the metformin group). Of those who completed 16 weeks of treatment, metformin use, as compared with placebo, was associated with improved glycemic control (mean daily glucose at 16 weeks 7.8 vs. 8.8 mmol/l, P = 0.006; mean GHb 6.9 vs. 7.6%, P < 0.0001); reduced insulin requirements (63.8 vs. 71.3 IU, P < 0.0001); reduced weight gain (-0.4 vs. +1.2 kg, P < 0.01); and decreased plasma LDL cholesterol (-0.21 vs. -0.02 mmol/l, P < 0.01). Risk of hypoglycemia was similar in both groups.

From the results it was concluded that, in type 2 diabetic patients who are intensively treated with insulin, the combination of insulin and metformin results in superior glycemic control compared with insulin therapy alone, while insulin requirements and weight gain are less.

Diabetes Care 25:2133-2140, 2002