Bactericidal activity and postantibiotic effect of clarithromycin and 14-hydroxyclarithromycin, alone and in combination, against Legionella pneumophila.

Time-kill curves using simulated peak and trough serum concentrations, and postantibiotic effect (PAE) were determined for clarithromycin and 14-hydroxyclarithromycin alone and in combination against four strains of Legionella pneumophila. Both compounds were bactericidal at both peak and trough concentrations. The combination at trough concentrations demonstrated lower killing activity than the parent drug in three of the four strains. PAE ranges were 7.28-17.3 h for clarithromycin, 6.78-14.77 h for the metabolite, and 5.15-13.23 h for the combination.