Efficacy and Safety Study of Saxagliptin + Metformin Immediate Release (IR) Versus Metformin IR Alone in Type 2 Diabetes Mellitus

Inclusion Criteria: * Type 2 diabetes * 18-78 years of age * Taking stable twice daily (BID) dosing of metformin IR (at least 1500 mg) for at least 8 weeks * A1C: 7-10% * C-peptide: ≥ 0.8 ng/mL * Body mass index (BMI): ≤45 kg/m\^2 Exclusion Criteria: * Women of childbearing potential unable or unwilling to use acceptable birth control * Women who are pregnant or breastfeeding * Fasting plasma glucose (FPG) \>270 mg/dL * Significant cardiovascular history * Symptoms of poorly controlled diabetes * History of diabetic ketoacidosis or hyperosmolar nonketotic coma * Insulin therapy within one year of screening * Cardiovascular even within the prior 6 months * New York Heart Association Stage III/IV congestive heart failure and/or known left ventricular ejection fraction \<=40% * Significant history of renal or hepatic disease * History of a psychiatric disorder, alcohol or drug abuse within the previous year * Treatment with potent CYP3A4 inhibitors or inducers * Immunocompromised participants * Active liver disease or clinically significant abnormal hepatic, renal , endocrine, metabolic, or hematological screening tests