Airway mucosa structure

Acute, heavy exposure to SM causes loss of the columnar cells of the upper respiratory tract, peribronchial edema, hyperemia of the blood vessels, cellular infiltrations in the submucosa, and intense vacuolization and disorganization of the cytoplasmic and nuclear structures (Emad and Rezaian, 1997, 1999). Pulmonary hemorrhage, pulmonary edema, and respiratory failure similar to ARDS may also occur. These cytotoxic effects are associated with acute thermal injury sustained by the airway mucosa and lead to scarring and development of stenosis of the tracheobronchial tree as was observed in 9.64% of the SM-exposed patients. 

Modification of the pharmacokinetics through structural alterations has provided several new steroids with a better GR affinity and therapeutic index and a lower bioavailability than the older drugs (Fig. 33.14). The new inhaled/intranasal glucocorticosteroids like mometasone furoate, budesonide and fluticasone propionate are more lipophilic than those used in oral and systemic therapy and have greater affinity for the GR than does dexamethasone as a consequence of their greater lipophilicity (43). Several of the topical corticosteroids, such as mometasone furoate, BDP, triamcinolone acetonide, and flunisolide, were reintroduced as inhalation and intranasal dosage forms for treatment of respiratory diseases (e.g., asthma or rhinitis). Inhaled budesonide and flunisolide are readily absorbed from the airway mucosa into the blood and are rapidly biotransformed in the liver into inactive metabolites. Mometasone furoate and fluticasone propionate are very potent anti-inflammatory steroids with an oral bioavailability of less than 1%. Obviously, the risk of systemic side effects for these newer corticosteroids is greatly reduced when compared with ... 

Particles are thought to stick to the viscous and sticky mucus. However, they do not just stick to the mucus, they appear to be displaced or even engulfed by the mucous layer. The surfactant film at the air-liquid interface is the first structural element of the airway mucosa that particles encounter at their deposition followed by retention. 

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