Mucociliary clearance drug retention time

Bioadhesive formulations and microsphere delivery systems in particular have attracted much attention. As drug formulations are usually rapidly removed from the site of deposition by the mucociliary clearance, increasing the retention time of drug in the nasal cavity via bioadhesion can increase bioavailability [28], Bioadhesion may be defined as the ability of a material (synthetic or biological) to adhere to a biological tissue for an extended period of time. When applied to a mucous membrane, a bioadhesive polymer may adhere primarily to the mucus layer or epithelial cell surface in a phenomenon known as mucoadhesion [29,30]. The bioadhesive properties of a wide range of materials have been evaluated over the last decade. 

Mucociliary clearance reduces the retention time of drugs within the nasal cavity and thus the opportunity for absorption. For drugs which are rapidly absorbed, mucociliary clearance is likely to be of little consequence, but for those compounds with physicochemical properties dictating slow absorption the effect of mucociliary clearance is likely to be profound. 

An alternative approach is to reduce the rate of mucociliary clearance and hence increase the retention time of the drug. This can be achieved by including an excipient in the formulation with a reversible ciliostatic effect such agents include certain preservatives. However, it is important that the chosen strategy does not permanently compromise mucociliary clearance, which would adversely affect airway homeostasis and defense. 

---