DPP4 and diabetes mellitus: The pharmacological therapy for DM comprises the administration of non-insulin antidiabetic drugs (NADs)—therapeutic subgroups identified by their respective Anatomical Therapeutic Chemical (ATC) classification [14]: biguanides, sulfonylureas, alpha-glucosidase inhibitors, thiazolidinediones, dipeptidyl peptidase 4 (DPP-4) inhibitors, glucagon-like peptide-1 (GLP-1) analogues, sodium-glucose co-transporter 2 (SGLT2); and insulins used for outpatient administration.