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The delivery of drugs to a target site frequently involves crossing biological barriers. The degree and nature of the impediment to flux, as well as the potential approaches to overcoming it, depend on the tissue, the drug, and numerous other factors. Here we present an overview of approaches that have been taken to crossing biological barriers, with special attention to transdermal drug delivery. Technology and knowledge pertaining to addressing these issues in a variety of organs could have a significant clinical impact.Biological barriers throughout the body present challenges for drug delivery. Chemical, physical, and biomolecule-mediated approaches to overcoming biological barriers have been developed for a variety of anatomic locations. The mechanisms and applications of these approaches are reviewed in this paper.

blood flow

Explanation:

An aqueous stagnant layer that overlies the apical membrane and the subepithelial blood flow are potential barriers to the absorption of drugs that readily penetrate the absorbing cell of the epithelium. The apical, basal, and basement membranes are potential barriers to the absorption of less permeable drugs.

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