Current Status of the Oral Delivery of Insulin

conducted involving a wide range of protein therapeutics for various conditions. Most of the proteins have been successfully applied in therapy, mainly as parenterals. An oral dosage form is the preferred form of delivery because of ease of administration, patient compliance, and cost. Major hurdles must be overcome before the oral delivery of a protein becomes a reality. Among the proteins, oral delivery of insulin has received the widest attention, yet no currently available oral insulin preparation exists. This article focuses on the oral delivery challenge of insulin as well as the advancements in its oral dosage form development, particularly in the past 25 years. Insulin was isolated from bovine pancreas in 1922 by Banting and Best, who received the 1923 Nobel Prize with Mcleod. Oral administration of insulin was found to be ineffective for the treatment of insulin-dependent diabetes mellitus. Since then the subcutaneous route has been the mainstay of insulin delivery until today. In early years, insulin was isolated mostly from the pancreases of bovine cadavers. This method of isolation led to several immunological reactions as a result of impurities present in the isolated protein. The synthesis of insulin by recombinant DNA technology represented an important scientific milestone and made large quantities of protein available at an affordable price — a factor that led to insulin becoming one of the most popular proteins to be studied for oral delivery. Consequently, research data in several aspects of delivery of insulin are available. The progress in the oral delivery of insulin could not have been possible without the help of research in areas such as analytical chemistry, immunoassays, biochemistry pharmaceutical sciences, novel methods of screening absorption in vitro by using isolated segments of animals and mammalian cells, and availability of functional polymers.