DPP4 and type 2 diabetes mellitus: We aimed to evaluate the efficacy and safety of the three dipeptidyl peptidase 4 (DPP-4) inhibitors (vildagliptin, sitagliptin, and linagliptin) as add-on therapy in Chinese patients with type 2 diabetes mellitus (T2DM)inadequately controlled on dual combination of insulin and metformin or acarbose.