Structural requirements for intestinal absorption of peptide drugs

The clinical development of orally active peptide drugs has been restricted by their unfavorable physicochemical characteristics, which limit their membrane permeation, and their lack of stability against enzymatic degradation. Successful oral delivery of peptides will depend, therefore, on strategies designed to alter the physicochemical properties of these potential drugs, without changing their biological activity, in order to circumvent the barrier properties of the intestinal epithelial cells. This manuscript will focus on the physical and metabolic barrier functions of the intestinal mucosa, the structural features of peptides which influence their passive diffusion and carrier-mediated transport, including efflux mechanisms, and various approaches used to prevent enzymatic degradation of the peptides and increase their permeability across the intestinal mucosa.