• Mean change in HbA1c from baseline to week 12
  

• Changes in fasting plasma glucose, insulin and glucagon, intestinal hormone levels, insulin sensitivity and beta cell function, lipid parameters; body weight and body mass index (BMI), blood pressure, treatment satisfaction score, safety evaluations
  

This is a randomized (assigned study drug by chance), double-blind (both the patient and investigator do not know whether patient is assigned to receive study drug or placebo), placebo-controlled study involving patients with Type 2 Diabetes Mellitus who are taking metformin. Patients are randomized to one of 4 treatment groups and receive study drug (R256918: 5 mg, 10 mg, or 15 mg twice daily) or placebo for a period of 12 weeks. The study consists of a screening period, a baseline visit, the treatment period of 12 weeks, and a follow-up visit. During the treatment period, patients visit the center every two weeks. On each visit, patients come to the clinic after 8 hours fasting. Effectiveness assessments from a blood sample include levels of fasting hemoglobin type A1c (HbA1c), glucose, cholesterol, triglycerides, insulin, C-peptide, and gastrointestinal hormones. Patients monitor their fasting blood glucose and record it in a diary. Insulin sensitivity and beta cell function are evaluated. Waist and hip circumference are measured. Safety evaluations, including incidence of adverse events, clinical laboratory results, vital signs, and electrocardiograms, are performed during the study. Patients complete a questionnaire related to treatment satisfaction of study medication. Patients receive dietary counseling and remain on a calorically appropriate, low fat diet during the entire study. Patients continue taking metformin in the same dose and according to the same dosing regimen as before the study. The overall duration of the study for each patient is approximately 18 weeks. The study hypothesis is that treatment with R256918 will improve glucose-dependent insulin secretion with weight loss improving insulin sensitivity and will be well tolerated in type 2 diabetic patients.