The biopharmaceutical aspects of nasal mucoadhesive drug delivery

Nasal drug administration has frequently been proposed as the most feasible alternative to parenteral injections. This is due to the high permeability of the nasal epithelium, allowing a higher molecular mass cut-off at appro ximately 1000 Da, and the rapid drug absorption rate with plasma drug profi les sometimes almost identical to those from intravenous injections. Despit e the potential of nasal drug delivery, it has a number of limitations. In this review, the anatomy and physiology of the nasal cavity, as well as cil iary beating and mucociliary clearance as they relate to nasal drug absorpt ion, are introduced. The rationale for nasal drug delivery and its limitati ons, some factors that influence nasal drug absorption, and the experimenta l models used in nasal drug delivery research are also reviewed. Nasal muco adhesion as a promising method of nasal absorption enhancement is discussed , and factors that influence mucoadhesion, as well as safety of nasal mucoa dhesive drug delivery systems are reviewed in detail. Nasal drug administration is presently mostly used for local therapies with in the nasal cavity. Anti-allergic drugs and nasal decongestants are the mo st common examples. However, nasal drug administration for systemic effects has been practised since ancient times. Nasally-administered psychotropic drugs by native Americans, the use of tobacco snuffs, and nasal administrat ion of illicit drugs such as cocaine are all well known (Illum & Davis 1992 ). Nowadays, the nasal cavity is being actively explored for systemic admin istration of other therapeutic agents, particularly peptides and proteins ( Illum 1992; Edman & Bjork 1992), as well as for immunization purposes (Lemo ine et al 1998). To better understand the basis for nasal drug absorption a nd factors that ran influence it, a brief review of the anatomy and physiol ogy of the nose is appropriate.