Therapeutic Efficacy of Triple Combination of Metformin, DPP4 Inhibitor and Thiazolidinedione in Drug-naïve Korean Type 2 Diabetic Patients

Thiazolidionedione, a PPARgamman agonist, is an strong insulin sensitizer. It has shown that durable glucose lowering effect and beta cell preservation. It is an important treatment option in patients with type 2 diabetes.

It has been well established that inhibition of dipeptidyl peptidase-4 (DPP-4) reduces blood glucose levels in both fasting and postprandial states, and preserves pancreatic β-cell function in patients with type 2 diabetes. The mechanism of action of DPP-4 inhibitors is to increase levels of active incretin, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), which stimulate insulin secretion as well as insulin biosynthesis while inhibiting glucagon release from pancreatic islets.

DPP4 inhibitors also have better safety and tolerability profiles (e.g., weight neutrality and less hypoglycemia) compared to other hypoglycemic agents. When considering combination therapy with DPP-4 inhibitors, metformin is the most commonly used agent which has been shown to be effective and well tolerated from previous studies. Besides the glucose lowering effect by reducing hepatic glucose output and improving insulin resistance, metformin without inhibiting DPP-4 activity,also increases active GLP-1 concentrations by 1.5- to 2-fold following an oral glucose load in obese, nondiabetic subjects. Accordingly, this effect of metformin may provide a unique benefit when combined with DPP-4 inhibitors through a substantial enhancement of the incretin axis, which provides effective and potentially additive glycemic improvement.

Because of its favorable pharmacological properties, combination of a DPP-4 inhibitor, metformin, and thiazolidinedione has been increasingly used to achieve rapid glycemic goal with low risk of hypoglycemia and no weight gain, and to delay the need for subsequent regimen changes. DPP-4 inhibitors block DPP-4 enzyme and preserve endogenous incretins whereas metformin increases the active form of GLP-1, both of which may enhance the secretory function of pancreas. However, the response to DPP-4 inhibitors and metformin combination therapy may be different in individuals according to their pancreatic function and insulin resistance status. In fact, previous studies with DPP-4 inhibitors showed different potency in glycemic controls depending on various patient characteristics including severity of diabetes and the use of other antidiabetic drug.Consequently, it would be clinically important to investigate effect of this triple combination therapy.