Nasal clearance in health and disease.

This paper reviews the anatomical and physiological factors of importance for nasal drug delivery and discusses in particular the influence of the nasal mucociliary clearance mechanism on the nasal absorption of drugs. The effect of nasal pathological conditions on the mucociliary clearance mechanism and the possible effect of such disease states on nasal drug transport are also discussed. Strategies for the exploitation of bioadhesive drug delivery systems and especially nasal absorption enhancers for the improvement of nasal drug delivery are evaluated to include considerations of the mechanism of action and correlation between the degree of bioadhesion and absorption enhancement and transport of drugs across the nasal membrane. A range of studies involving bioadhesive/absorption enhancer systems are detailed. A selected bioadhesive material, chitosan, which has been shown to have excellent absorption enhancer properties for a variety of drugs is discussed in some detail.