Celebrating a Century of Insulin Discovery: A Critical Appraisal of the Emerging Alternative Insulin Delivery Systems.

Since the discovery of insulin, continuous developments of this peptide have led to better management of diabetes mellitus, thus leading to a decrease in diabetes-related mortality. Despite these developments, we have seen an increase in diabetes cases, which has further necessitated more innovative methods for diabetes management. The subcutaneous administration of insulin remains the mainstay therapy for type 1 diabetes mellitus. However, despite the availability of insulin analogues with improved pharmacokinetics, challenges with conventional administration exist. The challenges associated with insulin injections include hypoglycaemic episodes, needle phobia, and injection-site inflammation, which all have been reported to reduce patient compliance. Ongoing research on diabetes management strives to develop therapies that provide improved glycaemic control with minimal side effects. In part, for these reasons, we have seen an increase in the search and development of alternative insulin delivery systems that are envisaged to circumvent the shortfalls associated with the conventional administration route. Several alternative drug delivery systems, such as oral, pulmonary, buccal, nasal, and transdermal, have been explored in the last century. These efforts have not been without victory, as we have seen the emergence of pulmonary (Exubera and Afrezza) and buccal insulin delivery systems licenced for therapeutic use. Despite the success seen in these two systems, their marketability and popularity have been severely compromised due to reported safety concerns. Although oral insulin delivery has always shown promise in the past decades; however, it was only limited to preclinical trials. The main challenge associated with this delivery route is poor bioavailability, which necessitates high insulin concentration to be administered. Due to recent developments, oral insulin has reached phase 3 clinical trials. It is believed that patients would prefer oral insulin as their preference is often observed for oral antidiabetics over injected ones. In the last decade, transdermal insulin has also gained interest, where delivery of insulin with a concomitant reduction in blood glucose concentration has been demonstrated in vivo. However, at present, there are no clinical studies that have reported the efficacy of transdermal insulin administration. With technological advancement, there is a potential to develop yet another insulin delivery system that would likely enter the markets. As these novel delivery systems have been found to be effective, emerging competing products should be welcome and appreciated.