Drug transfer through mucus.

Mucus is a complex aqueous mixture of glycoprotein, lipid, salts and cellular debris covering many epithelial surfaces in the human body. It affords protection for the underlying tissues from various environmental insults and the effects of enzymes or other chemical agents. In performing its functions, mucus may adversely affect the absorption or action of drugs administered by the oral, pulmonary, vaginal, nasal or other routes. The nature of mucous in normal and diseased states is summarized and discussed in this review. The study of the permeability of native or purified mucous gels is also important to understanding how it may alter the action or absorption of drugs that come in contact with epithelial surfaces. Various methods for studying mucous permeability and models for analyzing permeation data are discussed. A compilation of drug permeability data through various types of mucus is included. Drug binding to mucus is also important to understanding the relative importance of hindered diffusion versus drug binding to altered permeability through mucous layers. This is discussed with methods for and results of drug-mucus binding studies.