Dipeptidyl peptidase-4 inhibitors Dipeptidyl peptidase-4 inhibitors (eg, alogliptin, linagliptin, saxagliptin, sitagliptin) prolong the action of endogenous glucagon - like peptide-1 (GLP-1) by inhibiting the enzyme dipeptidyl peptidase-4 (DPP-4), which is involved in the breakdown of GLP-1.