The adhesion of pharmaceutical formulations to the mucosal tissue offers the possibility of creating an intimate and prolonged contact at the site of administration. This prolonged residence time can result in enhanced absorption and, in combination with a controlled release of the drug, also improved patient compliance by reducing the frequency of administration. During the almost 30 years over which mucoadhesion has been studied, a considerable amount of knowledge has been gained, and much has been learned about the different mechanisms occurring at the formulation-mucus interface and the properties that affect these mechanisms. The in-vivo performance of a dosage form not only depends on the mechanisms occurring at the interface, but also on the properties of the total mucoadhesive complex: the dosage form, the mucosa and the interface between them. A wide variety of methods are used for studying mucoadhesion; some rather similar to the in-vivo situation and some mimicking the interface alone. In this review, the mucus surface, the methods used for the study of mucoadhesion, the different mechanisms involved in mucoadhesion and theories underpinning them have been described. The complexity of mucoadhesion when trying to systemize the subject will also be discussed. The last part of the review describes the buccal, nasal, ocular, vaginal and rectal routes and provides examples of what can be achieved in-vivo when using mucoadhesive formulations.
