Intraphagocytic activity of erythromycin, roxithromycin and azithromycin.

The intraphagocytic activity of erythromycin, roxithromycin and azithromycin against phagocytosed Staphylococcus aureus was compared. Erythromycin and roxithromycin both acted bacteriostatically at concentrations corresponding to 10 X MIC. Azithromycin, however, did not prevent intracellular proliferation of the staphylococci. On comparison of the pH dependency of the antibacterial activity of the three drugs, azithromycin was found to be inactivated earlier in an acidic milieu.