The purpose of this study is to compare the effect of vildagliptin vs. pioglitazone to oxidative stress on daily blood glucose fluctuations, in patients with type 2 diabetes that was inadequately controlled by metformin.

Activation of oxidative stress by glucose fluctuations plays a major role in the pathogenesis of diabetic complication. Dipeptidyl peptidase IV (DPP-IV), such as vildagliptin, enhances glucose-induced insulin secretion, decreases glucagon secretion, and reduces postprandial hyperglycemia and may also improve acute fluctuations of glucose. We believe that vildagliptin may exert an effect of decreasing oxidative stress by reducing glucose excursion.

Inclusion Criteria:

• Male or female with age 18-80 years
• Type 2 diabetes mellitus
• On stable dose of metformin (more than 1000mg) for at least 1 month
• HbA1c 7~10%
• Subjects on statins, ACE inhibitors, ARBs and antioxidants will be allowed as long as they are on stable doses of these compounds and the dosage is not changed during the course of study
• BP under control - no change required to BP medications
• Agreement to maintain prior diet & exercise

Exclusion Criteria:

• Type 1 DM or Any kind of secondary DM
• Pregnant or lactating women.
• Treatment with sulfonylurea, α-glucosidase inhibitor, glinide, GLP-1 analogues, DPP-IV inhibitors or insulin therapy within 1 month prior to informed consent.
• Treatment with rosiglitazone or pioglitazone within 3 months prior to informed consent.
• HbA1c <7% or >10%
• Uncontrolled hypertension ( BP > 160/100 mmHg)
• Congestive heart failure (NYHA class I to IV).