Recent advances in protein and peptide drug delivery systems.

Delivery of therapeutic proteins/peptides has received a considerable amount of attention over the last 10 years, but there are number of limitations to oral delivery of proteins. The barriers to peptide bioavailability after oral administration are intestinal membrane permeability, size, intestinal and hepatic metabolism and lastly solubility. A number of approaches have been used to overcome these limitations. Poor membrane permeabilities of hydrophilic peptides might be overcome by structurally modifying the compound, thus increasing their membrane partition characteristics and their affinity for carrier proteins. Another approach is site specific delivery of the peptides to the most permeable part of the intestine. Metabolism (hepatic and intestinal) of peptides might be controlled by co-administration of competitive enzyme inhibitors, structural modifications and administration of the compound as well as absorbed prodrug that is converted into therapeutically active agent after its absorption. Various delivery systems like prolease technology, nano-particulate and microparticulate delivery system, mucoadhesive delivery of peptides and microspheres have been developed for the delivery of proteins and peptides. Non-conventional delivery systems for proteins are biodegradable and non-biodegradable systems. Besides these, some other approaches for protein and peptide delivery are vector mediated delivery of proteins using adenovirus, macroflux transdermal patches, pulmonary delivery of proteins, delivery of proteins and peptides across blood brain barrier.