Transmucosal Drug Delivery: Main Physiological Features and Modern Approaches

Mucosal membranes are located within all the major organs; therefore, they became a major target for drug delivery. The focus on transmucosal drug delivery systems (TDDS) has been increasing with new developments that promise localised drug delivery. TDDS offer a unique advantage compared to the oral route as first-pass metabolism will not be an issue. Furthermore, mucosal membranes have good permeability characteristics, which may result in better drug absorption and higher bioavailability. Transmucosal drug delivery is achieved by drug molecules penetrating the mucosal layer to reach their target site. However, the major limitation for TDDS is drug retention within the mucosa which can affect drug diffusion and permeability. Transmucosal drug delivery involves different delivery sites, each with special physiological characteristics. Therefore, different formulations with their own advantages and disadvantages which make them either suitable or unsuitable for a particular drug delivery pathway are needed. Research has shown that mucoadhesive polymers do improve retention of drugs within the mucosa thereby improving drug bioavailability. Moreover, PEGylation and nanocarrier-based formulations can enhance mucus penetration and can improve drug retention within the mucosal membranes leading to better bioavailability.