Comparison of Vildagliptin vs. Glimepiride on Glucose Variability in Metformin Uncontrolled Type 2 Diabetic Patients

Inclusion Criteria: 1. Patients who have given written informed consent to participate in the study. 2. Type 2 Diabetes Mellitus patients either Male or female from 18 - 75 years of age (both inclusive). 3. Patients who are uncontrolled on metformin monotherapy for at least past 4 weeks (1000-1500 mg daily and HbA1c \> 7.5 - 9%). 4. Patients with HbA1C levels within the range \> 7.5% - 9%. (If a past value is available within the last 12 weeks, it would be considered acceptable provided it was obtained after at least 4 weeks of metformin therapy 1000-1500 mg daily). Exclusion Criteria: 1. Age \> 75 years ; BMI \<22 or \>40 kg/m2 2. Patients who are on Insulin therapy at the time of study entry. 3. Type 1 Diabetes Mellitus patients. 4. Patients with severe renal (creatinine clearance \< 50 ml/min) or hepatic impairment (including pre-treatment ALT or AST \> 3 x ULN). Creatinine clearance will be estimated from serum creatinine using Cockcroft-Gault formula (Cockcroft and Gault, 1976) 5. Patients with contraindications as mentioned in the Summary of Product Characteristics (SPCs) for vildagliptin, metformin, glimepiride, vildagliptin plus metformin and glimiperide plus metformin. Other protocol defined inclusion/exclusion criteria may apply.