Pharmacokinetics and lung distribution of macrolide antibiotics in sepsis model rats.

Recent studies have shown azithromycin-specific clinical efficacy against macrolide-resistant strains of Streptococcus pneumoniae, despite the low susceptibility of the bacteria in vitro. This discrepancy complicates dosing and selection for treatment of macrolide-resistant strains. Although phagocyte delivery of azithromycin to inflamed tissues is considered a possible factor for clinical efficacy, there is a lack of sufficient evidence, and other pharmacokinetic factors under systemic inflammation may contribute.The concentrations of azithromycin, clarithromycin and erythromycin in the plasma and buffy coat were determined in normal and sepsis model rats. Furthermore, we compared the transport of the drug into the lung.The levels of all three macrolides in the buffy coat were higher than the levels in the plasma, and lower leukocyte counts in plasma were observed in septic rats, suggesting accumulation of the drugs per leukocyte was increased. The concentrations in the lung tissue of septic rats at each sampling time were the same as those in normal rats, and azithromycin-specific long-term stasis in the lung was evident.These results suggest that both the phagocyte delivery and the stasis of azithromycin in the lung could contribute to its clinical efficacy in treating infections caused by macrolide-resistant strains.