Anatomy, physiology and function of the nasal cavities in health and disease.

In studying drug absorption from the nasal mucous membrane, it is essential to have a clear understanding of anatomy and physiology of the nose, and how it relates to the characteristics of the delivery system used. The human nose is characterized by an individually varying shape and caliber, which might interfere with standard recommendations of intranasal medication. It is also of significance that there is a tendency for reflex- induced and profuse watery hypersecretion from glands, and for quick and considerable changes of mucosal thickness due to the presence of large venous sinusoids. These are factors which can interfere with pharmacokinetics. Also mucociliary transport rate has to be taken into consideration, as the drug is removed from the absorptive mucous membrane within 30 min. Intranasal drug distribution has been poorly studied in relation to nasal anatomy and pathology. In contrast to common believe, nasal inflammation does not seem to increase drug absorption. On the contrary, blockage, sneezing and rhinorrhoea might preclude the absorption.