Introduction: There are several hurdles to oral insulin delivery (OID): mainly, enzymatic proteolysis, gastric degradation, and an absorption barrier. Researchers have been attempting to overcome these natural barriers through chitosan-based insulin formulations.
Areas covered: In this paper, the authors review OID formulations to elucidate their techniques and evaluate their performance through a set of defined parameters and suggest overall outlooks and future directions. This review covers 86 articles and reveals that most oral insulin formulations were obtained through poly-electrolytic complexation or chemical modification techniques. The in-vitro results reported by the articles are mapped into a '30x70 performance window' to distinguish the best OID formulations. The review shows that most formulations were effective in addressing the gastric and enzymatic barriers but were not as effective in overcoming the absorption barrier of the gastrointestinal tract.
Expert opinion: Oral insulin delivery has been a topic of immense research with most efforts dedicated to developing a formidable insulin formulation that overcomes gastrointestinal tract barriers. While most OID formulations perform better under experimental conditions, their performance in in-vivo studies is not as effective. Thus, to make oral insulin delivery a reality, special attention is needed toward improving the in-vivo insulin absorption through the gut.
Keywords: chitosan; diabetes; drug delivery; oral insulin delivery.