We performed a prospective, randomized, multicenter trial to assess the efficacy and safety of combined treatment with mitiglinide and metformin for patients with type 2 diabetes who show inadequate glycemic control with metformin monotherapy. Subjects with HbA1c >7.0% after an 8-week metformin run-in phase were randomized to a 16-week trial phase with metformin plus mitiglinide (Met+Mit) or metformin plus placebo (Met).

This was a 16-week, randomized, double-blind study for comparing metformin plus mitiglinide (Met+Mit) versus metformin plus placebo (Met+Pcb). An 8-week metformin run-in phase (500 mg twice a day for the first 4 weeks and 500 mg three times a day for the following 4 weeks) was followed by a 16-week trial phase (mitiglinide 10 mg or placebo three times a day added to metformin 500 mg three times a day). The subjects with an HbA1c >7.0% at the end of the metformin run-in phase were randomized to a Met+Mit group or a Met+Pcb group of the trial phase.

Inclusion Criteria:

• aged 30-70 years
• had a duration of diabetes of <10 years
• body mass index (BMI) 20-35 kg/m2
• a plasma HbA1c level of 7.5-11% during the previous 4 weeks

Exclusion Criteria:

• subjects who were diagnosed with type 1 diabetes, gestational diabetes, or diabetes with any specific causes
• Subjects who had been treated with nateglinide, repaglinide, metformin (over 1,000 mg/day), or sulfonylurea (over a quarter of the maximum recommended dose) during the previous 8 weeks