Drug Uptake in the Trachea

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Abstract
For hydrophilic drugs and agents the major barrier to diffusion from the airway lumen into the mucosa is the epithelium, but for lipophilic agents epithelial permeability is high. Destruction of the epithelium increases the permeability of hydrophilic but not lipophilic agents. Changes in mucosal blood flow, induced either by vasoactive drugs or by changing the rate of arterial perfusion, lead to changes in drug uptake from the lumen to venous blood. Increases in flow decrease uptake, and vice versa for decreases in flow. The most likely explanation of this apparently paradoxical result is that increases in vascular pressure and flow result in a greater interstitial liquid volume and thus perfusion barrier, and induce solvent drag across the vascular endothelial wall, which will limit uptake of agents into the vascular lumen.