Safety and Efficacy of TAK-559 in Combination With Metformin in Patients With Type 2 Diabetes Mellitus.

Inclusion Criteria: * Diagnosed with type 2 diabetes mellitus, and on a stable dose of an oral antidiabetic monotherapy before Screening A. * Female patients of childbearing potential who were sexually active agreed to use adequate contraception, and could neither pregnant nor lactating from Screening throughout the duration of the study. * Had a glycosylated hemoglobin level greater than or equal to 8.0% and less than or equal to 10.0% at Screening B. * Had a fasting plasma glucose greater than or equal to 126 mg/dL (7.0 mmol/L) at Screening B. * Taking a stable dose of at least 1000 mg of metformin for at least 30 days before Screening B. * Had a stable or worsening self-monitoring blood glucose level while taking metformin. * Had a low-density lipoprotein less than 160 mg/dL (4.1 mmol/L) at Screening A. * Had a body mass index was less than or equal to 45 kg/m2 at Screening A. * Was willing to be counseled by the investigator or designee to follow an individualized, weight-maintaining diet during the study period. * Had evidence of insulin secretory capacity as demonstrated by a C-peptide concentration of greater than or equal to 1.5 ng/mL (0.50 nmol/L) at Screening A, and if necessary, after a repeat at Screening B. * Was able to perform daily self-monitoring blood glucose tests throughout the study. * Had a normal thyroid-stimulating hormone level of less than 5.5 μIU/mL (5.5 mIU/L) and greater than or equal to 0.35 μIU/mL (0.35 mIU/L) at Screening A. * Was in good health as determined by a physician (ie, via medical history and physical examination), other than a diagnosis of type 2 diabetes mellitus. * Had fasting clinical laboratory results within the normal ranges for the testing laboratory, or if not, the results were deemed not clinically significant by the investigator before Randomization. Exclusion Criteria: * Diagnosed with type 1 diabetes mellitus, hemochromatosis, or had a history of ketoacidosis. * Had any condition known to invalidate glycosylated hemoglobin results (eg, hemolytic states or hemoglobinopathies). * Took any disallowed medication, prescription medication, herbal treatment or over-the counter medication that may have interfered with evaluation of the study medication, including: * Insulin * Oral antidiabetics including sulfonylureas and alpha-glucosidase inhibitors * Systemic corticosteroids * Warfarin * Rifampin * St. John's Wort. * Thiazolidinediones * Peroxisome proliferator-activated receptor agonists * Nicotinic Acid * Fibrates * Had a history of myocardial infarction, coronary angioplasty or bypass graft, unstable angina pectoris, transient ischemic attacks, clinically significant abnormal electrocardiogram, or documented cerebrovascular accident within 6 months before Screening A. * Had abdominal, thoracic, or vascular surgery within 6 months before Screening A that in the investigator's opinion warranted exclusion from the study. * Had a creatine phosphokinase value greater than 3 times the upper limit of normal at Screening A. * Had persistent unexplained microscopic or macroscopic hematuria or a history of bladder cancer. * Had a triglyceride level greater than 500 mg/dL (5.6 mmol/L) at Screening A. * Received any alteration in allowed lipid lowering medication (dose or drug) within 2 months of Randomization, if applicable. The patient remained on a stable dose throughout the study. If deemed necessary, the dose could have been lowered with prior approval from the Sponsor. * Donated and/or received any blood or blood products within 3 months before Randomization. * Had a history of drug abuse or a history of alcohol abuse within 2 years before Randomization * Had a systolic blood pressure greater than 140 mm Hg or a diastolic blood pressure of greater than 95 mm Hg at Screening B. * Had significant cardiovascular disease including but not limited to, New York Heart Association Functional (Cardiac) Classification III or IV. * Had a history of cancer other than basal cell or stage 1 squamous cell carcinoma of the skin that had not been in remission within 5 years before Randomization. * Had an alanine aminotransferase or aspartate aminotransferase level greater than 3 times the upper limit of normal, active liver disease, or jaundice at Screening A. * Had a positive anti-hepatitis B surface antigen, or anti-hepatitis B e antigen test results at Screening A. * Was currently taking another investigational study medication or had taken an investigational study medication within 30 days before Screening A. * Had any other serious disease or condition at Screening A or at Randomization that might have affected life expectancy or made it difficult to successfully manage and follow the patient according to the protocol.