SITAGLIPTIN PHOSPHATE IS AN ORALLY-ACTIVE, POTENT, AND HIGHLY SELECTIVE INHIBITOR OF THE DIPEPTIDYL PEPTIDASE 4 (DPP-4) ENZYME FOR THE TREATMENT OF TYPE 2 DIABETES. THE DPP-4 INHIBITORS ARE A CLASS OF AGENTS THAT ACT AS INCRETIN ENHANCERS. BY INHIBITING THE DPP-4 ENZYME, SITAGLIPTIN INCREASES THE LEVELS OF TWO KNOWN ACTIVE INCRETIN HORMONES, GLUCAGON-LIKE PEPTIDE-1 (GLP-1) AND GLUCOSE-DEPENDENT INSULINOTROPIC POLYPEPTIDE (GIP). THE INCRETINS ARE PART OF AN ENDOGENOUS SYSTEM INVOLVED IN THE PHYSIOLOGIC REGULATION OF GLUCOSE HOMEOSTASIS. WHEN BLOOD GLUCOSE CONCENTRATIONS ARE NORMAL OR ELEVATED, GLP-1 AND GIP INCREASE INSULIN SYNTHESIS AND RELEASE FROM PANCREATIC BETA CELLS. GLP-1 ALSO LOWERS GLUCAGON SECRETION FROM PANCREATIC ALPHA CELLS, LEADING TO REDUCED HEPATIC GLUCOSE PRODUCTION.