Mucociliary clearance mechanisms

Aerosols must be respirable, that is, have a mean aerodynamic diameter of less than 5 xm, to ensure that a reasonable proportion will penetrate the respiratory tract defence systems of the nasal passages and the mucociliary clearance mechanisms. 

Substances deposited in the nasal cavity that are not readily absorbed are cleared in about 15 to 20 minutes by mucociliary clearance. The mucociliary clearance mechanism affects the absorption of polar drugs that have low permeability across membranes. This defense mecha-nism transports the particles down the throat. Mucociliary clearance can be affected by the drug moiety, formulation, hormones, and disease states.108... 

A number of ciliotoxicity studies have pointed out a low correlation between the results obtained using different in vitro and in vivo methods [121], The effects of nasal formulations on the ciliary beat frequency in vitro are usually more expressed than in vivo, since in vivo, cilia are partially protected by the mucous layer and investigated formulation is eventually cleared from the nasal cavity due to the mucociliary clearance mechanism. Also, toxic effects of the formulations on the cilia in vivo may be reversible due to the constant nasal mucosal cell turnover [121]. 

In order to address the rapid removal of pharmaceuticals due to the mucociliary clearance mechanism, mucoadhesive systems that promote bioadhesive interactions with a mucous membrane and increase retention time by prolonging the contact between the formulation and absorption site have been evaluated as a strategy to enhance systemic absorption following... 

A common complication of persistent hypersecretion and mucus plugging is a less effective mucociliary clearance mechanism. Inhaled bacteria which are normally quickly cleared from the bronchial system have greater opportunity for tissue invasion. Chronically affected asthmatics are more likely to develop bacterial bronchitis. It is not unusual for CB to become superimposed on the asthma as a consequence of these infections. Interestingly asthmatics who get an acute bacterial bronchitis will often note an improvement of their asthmatic symptoms. 

The mucociliary clearance mechanism is generally recognised as a defence against infectious agents and a means to remove inhaled particulate matter. Inhaled particles reach different locations in the lung depending on their size. Above 5 [an, the conducting airways filter dusts, where ciliated and mucous cells cooperate and waft the particles upwards. 

Isawa T, Teshima T, Hirano T, Ebina A, Konno K. Mucociliary clearance mechanism in smoking and nonsmoking normal subjects. JNucl Med 1984 25 352-359. 

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