Sitagliptin is a Dipeptidyl-peptidase-4 (DPP-4) inhibitor approved by the FDA as monotherapy or in combination with metformin for the treatment of type 2 diabetes. Metformin and sitagliptin are active within 24 hours of initiation and do not cause hypoglycemia. Sitagliptin works by slowing the inactivation of glucagon-like peptide-1 (GLP-1). GLP-1 stimulates glucose dependent secretion of endogenous insulin with meals.