Cell penetration: One of the main features of macrolides is their capa
city to penetrate host cells. This properly is the basis of their acti
on against intracellular microorganisms and can explain characteristic
pharmacokinetics as well as interference with cell metabolism. Intrac
ellular concentration: Erythromycin A derivatives with a single base g
roup (roxithromycin) accumulate rapidly to a saturation point both in
the cytoplasm and in granulations. Intracellular concentrations of der
ivatives with two base groups do not reach saturation due to slow effl
ux. Therapeutic action: Because of their intracellular concentration,
macrolides are indicated for the treatment of cell-associated pathogen
s. Exflux allows possible selective transfer into infected tissues. Ma
crolides also have an effect on functional activity of the host cells.