Efficacy and Safety Study of SYR-619 in Treating Subjects With Type 2 Diabetes Mellitus

Inclusion Criteria: * Male or female, with a historical diagnosis of type 2 diabetes mellitus. * Treatment for diabetes with either lifestyle modification or metformin or sulfonylurea alone for at least the 2 months prior to Screening; and a stable dose of either metformin or sulfonylurea for at least 12 weeks prior to randomization for subjects receiving metformin or sulfonylurea at Screening. * Those subjects receiving metformin or sulfonylurea monotherapy at randomization must have been at least 75% compliant with their metformin or sulfonylurea regimen during the run in/stabilization period, as assessed by subject diary and investigator assessment. * No treatment with antidiabetic agents other than metformin alone or sulfonylurea alone within the 3 months prior to Screening. * Glycosylated hemoglobin concentration between 7.0% and 10.0%, inclusive, and a fasting plasma glucose \<275 mg/dL (\<15.27 mmol/L) at the Week -1 visit. * Body mass index ≥23 and ≤45 kg/m2. * Fasting C-peptide concentration ≥0.8 ng/mL (≥0.26 nmol/L). (If this screening criterion is not met, the subject still qualifies if C-peptide ≥1.5 ng/mL \[≥0.50 nmol/L\] after a challenge test). * If regular use of other non-excluded medications, must be on a stable dose for at least the 4 weeks prior to Screening. However, as needed use of prescription or over-the-counter medications is allowed at the discretion of the investigator. * Systolic blood pressure \<160 mm Hg and diastolic pressure \<100 mm Hg. * Hemoglobin ≥12 g/dL (≥120 gm/L) for males and ≥10 g/dL (≥100 gm/L) for females. * Alanine aminotransferase ≤3 x upper limit of normal. * Serum creatinine \<1.5 mg/dL (\<133 micromol/L) for males and \<1.4 mg/dL (\<124 micromol/L) for females. * Urine albumin/creatinine ratio of \<1000 μg/mg (113 mg/mol) at Screening. If elevated, the subject may be rescreened within 1 week. * Thyroid-stimulating hormone level ≤ the upper limit of the normal range and the subject has normal thyroid function (clinically euthyroid) * A female subject of childbearing potential who is sexually active must agree to use adequate contraception, and must be neither pregnant nor lactating from Screening and throughout the duration of the study. * Able and willing to monitor their own blood glucose concentrations with a home glucose monitor. * No major illness or debility that in the investigator's opinion prohibits the subject from completing the study. Exclusion Criteria: * Concurrently treated with combined metformin and sulfonylurea antidiabetic therapy. * History of cancer, other than squamous cell or basal cell carcinoma of the skin, that has not been in full remission for at least 5 years prior to Screening. * History of laser treatment for proliferative diabetic retinopathy within the 6 months prior to Screening. * History of treated diabetic gastric paresis. * New York Heart Association Class III or IV heart failure regardless of therapy. * Currently treated subjects who are stable at Class I or II are candidates for the study. * History of coronary angioplasty, coronary stent placement, coronary bypass surgery, or myocardial infarction within the 6 months prior to Screening. * History of any hemoglobinopathy that may affect determination of glycosylated hemoglobin. * History of infection with hepatitis B, hepatitis C, or human immunodeficiency virus. * History of a psychiatric disorder that in the investigator's opinion will affect the subject's ability to participate in the study. * History of alcohol abuse or substance abuse within the 2 years prior to Screening. * The subject is required to take or intends to continue taking any disallowed medication, any prescription medication, herbal treatment or over-the counter medication that may interfere with evaluation of the study medication, including: * Treatment with antidiabetic agents other than study drug or metformin or sulfonylurea is not allowed within the 3 months prior to Screening and through the completion of the end-of-treatment/early termination procedures. * Treatment with weight-loss drugs, any investigational antidiabetic drugs, or oral or systemically injected glucocorticoids is not allowed from 3 months prior to randomization through the completion of the end-of-treatment/early termination procedures. * Receipt of any investigational drug within the 30 days prior to Screening or a history of receipt of an investigational antidiabetic drug within the 3 months prior to Screening. * Prior treatment in an investigational study of SYR-619 or alogliptin. * The subject has a known hypersensitivity to any compound related to SYR-619 or alogliptin.