Penetration of erythromycin in respiratory tract infections.

ABSTRACT

Successful treatment of respiratory tract infections with erythromycin may depend upon adequate penetration of the drug to the site of infection. The delivery of antibiotics into respiratory tract secretions is a simple passive diffusion process along a concentration gradient according to Fick's principle. A number of other factors including physicochemical characteristics of the drug and host defence mechanisms may further modify the tissue penetration. A common feature of penetration studies in respiratory tract infections is the wide range of results. This is due to the numerous variables involved in this kind of study. However, the studies performed at steady state, and after oral administration of erythromycin, show a rapid increase in drug concentrations in adenoid and tonsillar tissue homogenates and sustained levels equal to or higher than in serum. In secretions of the middle ear, paranasal sinuses and bronchiae the penetration and elimination of erythromycin is much slower. The drug levels were equal to--or in some cases even higher than--steady state serum concentrations. Fluctuations, however, were less pronounced. In lung tissue homogenates erythromycin concentrations higher than the serum levels have generally been found. In respiratory tract secretions and tissues the penetration of erythromycin is good. Sufficient levels are reached to inhibit in vitro the growth of most common pathogens involved in respiratory tract infections with the exception of some strains of Haemophilus influenzae.