Mucoadhesive drug delivery systems: a promising non-invasive approach to bioavailability enhancement. Part I: biophysical considerations.

Introduction: Mucoadhesive drug delivery systems (MDDS) are specifically designed to interact and bind to the mucosal layer for localized, prolonged, and/or targeted drug delivery. Over the past 4 decades, different sites have been explored for mucoadhesion including the nasal, oral, and vaginal cavities, the gastrointestinal tract and ocular tissues.

Areas covered: The present review aims to provide a comprehensive understanding of different aspects of MDDS development. Part I focuses on the anatomical and biological aspects of mucoadhesion, which include a detailed elucidation of the structure and anatomy of the mucosa, the properties of mucin, the different theories of mucoadhesion and evaluation techniques.

Expert opinion: The mucosal layer presents a unique opportunity for effective localization as well as systemic drug delivery via MDDS. Formulation of MDDS requires a thorough understanding of the anatomy of mucus tissue, the rate of mucus secretion and turnover, and the physicochemical properties of mucus. Further, the moisture content and the hydration of polymers are crucial for interaction with mucus. A confluence of different theories used to explain the mechanism of mucoadhesion is useful for understanding the mucoadhesion of different MDDS and their evaluation is subject to factors, such as the site of administration, type of dosage form, and duration of action. [Figure: see text].