DPP4 and diabetes mellitus: Sitagliptin phosphate monohydrate ((R)-3-Amino-1-(3-(trifluoromethyl)-5,6-dihydro-[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl)-4-(2,4,5-trifluorophenyl)butan-1-one phosphate monohydrate, a treatment for type 2 diabetes mellitus, is the first commercially commercialized oral hypoglycemic agent among dipeptidyl peptidase-4 (DPP-4) inhibitors and is taken as monotherapy or combination therapy at a dose of 100 mg once a day [13].