Antimicrobial activities and postantibiotic effects of clarithromycin, 14-hydroxy-clarithromycin, and azithromycin in epithelial cell lining fluid against clinical isolates of Haemophilus influenzae and Streptococcus pneumoniae

The antimicrobial activity of concentrations of selected macrolides found in epithelial cell lining fluid was investigated. Clarithromycin demonstrated greater potency and a significantly longer postantibiotic effect (PAE) than azithromycin against Streptococcus pneumoniae. Azithromycin displayed greater potency, faster killing, and a longer PAE than clarithromycin against Haemophilus influenzae. Drug concentrations in epithelial cell lining fluid similar to those found in tissue did not improve the synergistic potential of 14-hydroxy-clarithromycin and indicate that a maximal PAE may exist despite increasing concentrations of drug.