Pulmonary drug delivery metabolism

Keywords Pneumocytes Pulmonary drug delivery Pulmonary metabolism, Alveolar epithelium... 

The systemic availability of an inhaled glucocorticoid represents the additive and complex combination of pulmonary and gastrointestinal drug absorption. Absorption is influenced by many factors, including delivery device, the use of a spacer, the particle size of the inhaled drug, and the absorption and metabolism of the swallowed drug (1). 

During oral drag absorption, metabolism can occur in the enterocyte cells that line the lumen of the intestine and in the liver before a drug enters the systemic circulation. Loss of drug in either of those locations constitutes first pass elimination . This first-pass effect can be observed for any type of extravascular delivery (nasal, pulmonary, rectal, vaginal, etc.). The magnitude of the first-pass elimination can be quite different in different tissues. However, the most common site for first-pass metabolism is the gut and liver. Once a drug enters the systemic circulation, most of its metabolic elimination occurs in the liver. Consequently, much of the literature on metabolism centers on hepatic metabolism. 

Taljanski W, Pierzynowski SG, Lundin DPD, Westrom BR, Eirefelt S, PodneslyJ, Dahlback M, Siwinska-Golebiowska H, and Karlsson BW. Pulmonary Delivery of Intratracheally Instilled and Aerosolized Cyclosporine A to Young and Adult Rats. Drug Metabolism and Disposition 1997 25(8) 917-920. 

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