ABSTRACT
Interest in the manner in which solutes cross the pulmonary epithelium has grown with the recognition that the lungs can be used as a convenient portal for administering medications that are currently injected because they cannot be absorbed from the gut. It has long been understood that gases (e.g., amyl nitrite and carbon monoxide) and lipid-soluble solutes (e.g., nicotine and alcohol vapor) can be readily absorbed through the lungs, but it was thought that absorption of nonvolatile and lipid-insoluble molecules, such as proteins, would be too slow to permit effective therapy. This problem has been overcome with modified pharmaceuticals and the use of new devices that can deliver larger doses of these medications (most notably insulin). However more information is needed regarding the factors that influence the rates at which these molecules traverse the barriers separating the gaseous and blood compartments of the lungs. The enormous surface area and attenuated membranes of the alveolar compartment of the lungs suggests that aerosols containing medications for extrapulmonary treatment should be designed to reach the alveolar compartment, and this review will be concerned with absorption of solutes from the distal regions of the lungs.
