Vildagliptin 100 mg Once Daily vs. Placebo as add-on Therapy in Patients With Type 2 Diabetes Inadequately Controlled With Metformin

Inclusion Criteria: * Male, non-fertile female or female of childbearing potential using a medically approved birth control method * Patients who have received metformin for at least three months prior to visit 1 and have been on a stable dose for a minimum of 8 weeks prior to visit 1 * Agreement to maintain the same dose of metformin throughout the study * Age in the range of 18-85 years inclusive. * HbA1c in the range of 6.5 - 8.0% (inclusive) at visit 1 * Agreement to maintain prior diet and exercise habits during the full course of the study * Ability to comply with all study requirements and signed informed consent to participate in the study. Exclusion Criteria: * Pregnant or lactating female A history of: * type 1 diabetes, diabetes that is a result of pancreatic injury, or secondary forms of diabetes, e.g. Cushing's syndrome and acromegaly. * acute metabolic diabetic complications such as ketoacidosis or hyperosmolar state (coma) within the past 6 months. Any of the following significant laboratory abnormalities: * ALT, AST greater than 2 times the upper limit of the normal range at visit 1. * Direct bilirubin greater than the upper limit of the normal range at visit 1. * Serum creatinine levels equal to or greater than 1.5 mg/dL (132 umol/L) males, equal to or greater than 1.4 mg/dL (123 umol/L) females, or a history of abnormal creatinine clearance at visit 1. * Clinically significant TSH values outside of normal range at visit 1. * Clinically significant laboratory abnormalities, confirmed by repeat measurement, other than hyperglycemia, hyperinsulinemia, and glycosuria at visit 1 Treatment with any oral anti-diabetic other than metformin within 3 months prior to visit 1 Other protocol-defined inclusion/exclusion criteria may apply