Optimising oral systems for the delivery of therapeutic proteins and peptides

Therapeutic proteins/peptides are mostly administered as parenteral (injectable) preparations as a result of their poor oral bioavailability which is due to degradation by proteolytic enzymes, poor membrane permeability and large molecular size. However, the oral route would be preferred to theparenteral administration because it is more convenient for   self-administration, non-invasive and more patient friendly. Consequently, efforts have intensified over the past two decades to maximize theextent of absorption of protein and peptide drugs in order to achieve optimum bioavailability via the oral route. A suitable oral delivery system should retain the drug and maintain its integrity until it gets to the region of maximum absorption where the protein/peptide is released. It would be advantageous for such a delivery system to be capable of attaching itself to the absorptive cells in that region during the course of drug release by means of specific interactions with the tissue components. Furthermore,movement of drug should be independent of prevailing factors in the gut during passage. This review examines the various efforts and strategies that have been used to pursue the goals of effective oral peptide delivery, progress made so far, as well as current trends and future prospects. Relevant issues and phenomena such as membrane permeability control, intestinal absorption, paracellular pathway and targeting have also been discussed