Drug Absorption in the Lung

The pulmonary lymphatic system contributes to the clearance of fluid and protein from the lung tissue interstitium and helps to prevent fluid accumulation in the lungs [108], The lymphatic endothelium allows micron-sized particles (e.g. lipoproteins, plasma proteins, bacteria and immune cells) to pass freely into the lymph fluid [103], After administration of aerosolised ultrafine particles into rats, particles were found in the alveolar walls and in pulmonary lymph nodes [135], which suggests that drainage into the lymph may contribute to the air-to-blood transport of the inhaled particles. 

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Inhalation (IH) The administration of volatile gases and vapours, followed by drug absorption in the lungs or nasal mucosa. Examples include general anaesthetics like nitrous oxide, nicotine from the tar droplets in tobacco smoke, cannabinoids from cannabis leaf smoke and various opiates from burning opium resin. 

In relation to systemic absorption of drugs, absorption in the lung can be described as the passage of a series of barriers by the drug in order to enter the systemic circulation. It is important to realize that physiological conditions in the lung differ widely from site to site. Major physiological factors that affect pulmonary absorption are [10] ... 

Figure 6.5 Relationship between drug absorption in vivo and airspace to perfusate transfer in the isolated perfused lung [142].

Cheek, J.M., Kim, K.-J., and Crandall, E.D., NOj decreases paracellular resistance to ion and solute flow in alveolar epithelial monolayers, jcp. Lung Res., 16 561-575 (1990). Rangachari, P.K., Prior, T., and MeWade, D., Epithelial and mucosal preparations from canine eolon responses to substanee P, J. Pharmacol Exp. Ther., 254 1076-1083 (1990). Tomita, M., Hayashi, M., Toshiharu, H., and Awazu, S., Enhancement of colonic drug absorption by the transcellular permeation route, Pharm. Res., 5 786-789 (1988). 

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