Antibiotics and mucous membrane: pharmacokinetic aspects.

The penetration of chemoantibiotic agents across the mucous membrane is affected by several factors, some of which are related to the drug and others to the membrane. Molecular weight can influence the penetration of chemoantibiotic agents into mucous membranes. Liposolubility is another factor which can enhance the penetration of chemoantibiotic agents. Factors related to the membrane can affect diffusion of the antibiotic. Inflammation of the mucous membrane enhances the volume of blood circulating within tissues and, as a consequence, the rate of drug penetration into them. This condition, however, can be counterbalanced by a high binding rate of the drug to tissues. The pH affects the action of antibacterial agents. Acid pH range enhances the antibacterial activity of beta-lactams, an alkaline range that of macrolides. Besides purely physiochemical factors, there are others able to interfere with the diffusion of a chemoantibiotic agent into and through the mucous membranes. The diffusion into bronchial membrane and the penetration through the hematobronchial barrier seems to occur substantially by means of a passive transfer. There is therefore an establishment of a proportionality relationship between the concentrations in the two blood-bronchial fluid compartments. Exceptions to this rule seem to be some drugs like macrolides, even if a real active transfer mechanism has not yet been demonstrated. A precise knowledge of its pharmacokinetic parameters is an indispensable condition for the characterization of a molecule which penetrates the mucous membranes.