Oral Absorption Promoters: Opportunities, Issues, and Challenges

Transport of a drug across the biological membrane of the gastrointestinal tract has turned out to be a critical barrier against the success of any oral drug delivery technology. The unique advantages of the oral route, along with need for an oral substitute of invasive parenteral formulations and the reduction of intersubject variability in plasma profiles, has been an incentive for the use of excipients with absorption-enhancing properties to boost the bioavailability of poorly absorbed drugs. The development of such excipients is not a simple task, so understanding enhancement mechanisms in relation to physiology can facilitate the identification of structure-function relationships as well as the development of newer agents for customary applications. The literature is replete with reports of absorption promoters, the selection of which is influenced by the mechanisms, safety, pharmacological inertness, rapidity of action, reversibility of induced membrane alterations and excipient compatibility. Despite promising results in preliminary screenings, the development process is hindered by low reproducible efficacy and pharmacologically driven safety issues. In this review, we elaborate on the importance of permeation enhancers in oral drug delivery, their current status, and issues at the forefront of the development of formulations using absorption promoter technologies.