Sitagliptin (INN; /sɪtəˈɡlɪptɪn/ , previously identified as MK-0431 and marketed as the phosphate salt under the trade name Januvia) is an oral antihyperglycemic (antidiabetic drug) of the dipeptidyl peptidase-4 (DPP-4) inhibitor class.It was developed, and is marketed, by Merck & Co.This enzyme-inhibiting drug is used either alone or in combination with other oral antihyperglycemic agents (such as metformin or a thiazolidinedione) for treatment of diabetes mellitus type 2.here have been several postmarketing reports of pancreatitis (some fatal) in people treated with sitagliptin and other DPP-4 inhibitors, and the U.S. package insert carries a warning to this effect, although the causal link between sitagliptin and pancreatitis has not yet been fully substantiated.