Oral delivery of insulin for treatment of diabetes: Classical challenges and current opportunities

Abstract

Oral dosage form is the most common form of delivery systems due to several benefits such as ease of manufacturing, ease of administration, better formulation stability and patient compliance. Recently many proteins and peptides have been investigated for their usefulness in therapy, but mainly as parenterals due to the associated inherent problems, for instance its rapid degradation, low permeability and absorption in gastrointestinal tract. These problems must be solved or minimized to an extent that would be clinically significant before the oral delivery of proteins and peptides becomes a reality. Among the proteins, oral delivery of insulin has been attempted extensively but without much success so far and yet no formulation with oral delivery of insulin could be marketed. Several approaches have been developed to enhance oral absorption of insulin, such as inhibition of acidic and enzymatic degradation, enhancement of membrane permeability or widening of tight junctions, enhancement of insulin uptake and development of novel insulin carriers. This review article mainly focuses on the classical challenge of oral delivery of insulin and different strategies to overcome the related issues. Moreover, the current drug delivery technologies adopted in an attempt to develop practicable oral insulin have been discussed.