It is well established that inhibition of dipeptidyl peptidase (DPP)-IV reduces glucose levels and preserves pancreatic beta cell function in patients with type 2 diabetes. DPP-IV inhibitors stimulate insulin secretion as well as insulin biosynthesis and inhibit glucagon secretion from pancreas by increasing incretin (GLP-1) levels. Recent studies reported that combination therapy with DPP-IV inhibitors and other oral antidiabetic medication 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 glucose lowering effect of DPP-IV inhibitors in patients with type 2 diabetes on insulin treatment.

The researchers hypothesized that DPP-IV inhibitor add-on therapy to insulin treatment may have favorable effects on glucose control and endogenous insulin secretory function in type 2 diabetic patients. The researchers plan to compare between sitagliptin (DPP-IV inhibitor) add-on therapy and insulin dose increase therapy in uncontrolled type 2 diabetes on insulin treatment.

Inclusion Criteria:

• Type 2 diabetes
• HbA1c ≥ 7%
• Age ≥ 18
• Insulin treatment with or without oral antidiabetic medication

Exclusion Criteria:

• Contraindication to sitagliptin
• Pregnant or breast feeding women
• 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
• 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