Efficacy and Safety of Gosogliptin as Monotherapy and in Combination With Metformin vs. Vildagliptin as Monotherapy and in Combination With Metformin in Drug-naive Type 2 Diabetic Patients.

Inclusion Criteria: 1. Men and women from 18 through 78 years 2. Confirmed clinical diagnosis of type 2 diabetes mellitus 3. Drug-naive patients or patients without hypoglycemic drug treatment at least till 12 weeks before screening 4. Patient's agreed to use adequate methods of contraception during the study 5. Body mass index 22-40 kg/m2 6. HbA1c 7.5 - 11.0% 7. FPG \< 15 mmol/L 8. Signed informed consent 9. Patient's ability to follow all protocol requirements Exclusion Criteria: 1. Pregnancy and lactation, women who plan to become pregnant during the clinical study, women of child-bearing potential (i.e. non-stylized surgically and in period of post menopause less than 2 years) without adequate methods of contraception. 2. History of type 1 diabetes mellitus and other forms 3. Severe metabolic complications of diabetes as ketoacidosis, hyperosmolar coma during 6 weeks before screening 4. Severe complication of diabetes, for instance proliferative retinopathy in active stage, autonomic neuropathy or gastroparesis 5. A known allergy, hypersensitivity or contraindications to Gosogliptin, Vildagliptin, Metformin or their components 6. Convulsive disorder; system autoimmune diseases or vascular collagenosis demanding the previous or current treatment by systemic corticosteroids, cytostatics; malignancy within the last 5 years (except for a basal-cell carcinoma); 7. Significant cardiovascular diseases within 12 months of screening including: chronic heart failure of a class III or IV (NYHA), severe arrhythmia demanding treatment with antiarrhythmics, unstable angina, myocardial infarction, heart and coronary vessels surgery, heart valves diseases, transitory ischaemic attack or stroke, uncontrolled arterial hypertension with systolic Blood Pressure \> 180 mm Hg and diastolic Blood Pressure \> 110 mm Hg, pulmonary embolism or deep venous thrombosis 8. A nephrotic syndrome, a chronic renal failure, serum creatinine \> 1.5 mg/dL (132 µmol/L) in men and \> 1.4 mg/dL (123 µmol/L) in women or GFR \<60 ml/min/1.73m2 9. HBV, HCV or a liver cirrhosis; AST or ALT \> 3 ULN; total bilirubin \> 2 ULN 10. HIV; severe infection that can affect glycemia within 30 days of screening 11. Anemia (Hb ≤10.5 g/dL in women or ≤11.5 g/dL in men); loss of \> 1 unit of blood ( 500 mL) or blood transfusion within 12 weeks of screening 12. Drugs or alcohol abuse 13. Administration of any study drug within 30 days of screening 14. Inability to read or write; unwillingness to understand and follow the protocol procedures