It is well established that inhibition of dipeptidyl peptidase (DPP)-IV reduces glucose levels in both fasting and postprandial states and preserves pancreatic beta cell function in patients with type 2 diabetes. Their mechanism of action is derived from increased incretin (GLP-1) levels, which stimulate insulin secretion as well as insulin biosynthesis and inhibit glucagon secretion from pancreas. Recent studies reported that combination therapy with DPP-IV inhibitors and metformin have additive or synergistic effects in lowering glycose level, preserving beta-cell mass and function as well as enhancing insulin sensitivity. However, there have been few studies about the difference of glucose lowering effect of combination therapy of DPP-IV inhibitors and metformin according to the secretory capacity of pancreas.

The researchers hypothesized that combination therapy with DPP-IV inhibitor and metformin may have more favorable glucose lowering effect in type 2 diabetic patients who have preserved pancreatic secretory function. The researchers plan to investigate the difference of glucose lowering effect of 24 weeks treatment with sitagliptin (DPP-IV inhibitor) in combination with metformin according to basal c-peptide and glucagon level in type 2 diabetic patients.

Inclusion Criteria:

• Type 2 diabetes
• HbA1c ≥ 7%
• Age ≥ 18

Exclusion Criteria:

• Contraindication to sitagliptin or metformin
• Pregnant or breast feeding women
• Reproductive-age women who refuse contraception
• Type 1 diabetes, gestational diabetes, or diabetes with secondary cause
• Chronic hepatitis B or C (except healthy carrier of HBV), liver disease (AST/ALT > 3-fold the upper limit of normal)
• Renal failure (Cr > 2.0)
• Cancer within 5 years (except squamous cell cancer, cervical cancer, thyroid cancer with appropriate treatment)
• Not appropriate for oral antidiabetic agent
• Medication which affect glycemic control
• Disease which affect efficacy and safety of drugs
• Other clinical trial within 30 days