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 i n epithelial cell lining fluid was investigated. Clarithromycin demonstrate d greater potency and a significantly longer postantibiotic effect (PAE) th an azithromycin against Streptococcus pneumoniae. Azithromycin displayed gr eater potency, faster killing, and a longer PAE than clarithromycin against Haemophilus influenzae. Drug concentrations in epithelial cell lining flui d similar to those found in tissue did not improve the synergistic potentia l of 14-hydroxy-clarithromycin and indicate that a maximal PAE may exist de spite increasing concentrations of drug.