In vitro and in vivo uptake of azithromycin (CP-62,993) by phagocytic cells: possible mechanism of delivery and release at sites of infection

Abstract

Azithromycin, a novel azalide antibiotic, concentrated in human and mouse polymorphonuclear leukocytes (PMNs), murine peritoneal macrophages, and mouse and rat alveolar macrophages, attaining intracellular concentrations up to 226 times the external concentration in vitro. In murine peritoneal macrophages, azithromycin achieved concentration gradients (internal to external) up to 26 times higher than erythromycin. The cellular uptake of azithromycin was dependent on temperature, viability, and pH and was decreased by 2,4-dinitrophenol. Azithromycin did not decrease phagocyte-mediated bactericidal activity or affect PMN or macrophage oxidative burst activity (H202 release or Nitro Blue Tetrazolium reduction, respectively). Azithromycin remained in cells for several hours, even after extracellular drug was removed. However, its release was significantly enhanced by phagocytosis of Staphylococcus aureus (82 versus 23% by 1.5 h). In vivo, 0.05 ,ig of azithromycin was found in peritoneal fluids of mice 20 h after oral treatment with a dose of 50 mg/kg. Following caseinate-induced PMN infiltration, there was a sixfold increase in peritoneal cavity azithromycin to 0.32 ,ug, most of which was intracellular. Therefore, the uptake, transport, and later release of azithromycin by these cells demonstrate that phagocytes may deliver active drug to sites of infection.

Single-dose azithromycin for acute otitis media: a pharmacokinetic/pharmacodynamic rationale

“…However, after 24 hours of incubation in drug-free medium, Ͼ90% of intracellular drug was released into the medium ( Figure 3). 8 More recently, studies using rat embryo fibroblasts and epithelial-like rat kidney cells have confirmed these results. 5 Thus, the opposing forces of intracellular accumulation and extracellular release create a dynamic equilibrium, resulting in the high, sustained tissue concentrations and long half-life characteristic of azithromycin.…”

“…In human fibroblasts and mouse macrophages, the entry of drug into the cell is rapid, and the intracellular concentration is proportional to both time of incubation and extracellular concentration (Figure 2). 4,8 This linear relationship suggests a nonsaturable process. Inhibitors of glycolysis and oxidative metabolism do not affect the entry process, nor is it affected by inhibitors of known membrane-transport systems for nucleosides, hexoses, or amino acids.…”

“…The ability of azithromycin to accumulate intracellularly has been demonstrated in fibroblasts, 4 epithelial cells, 6,7 and macrophages, 8 cell types found …”

“…In addition, azithromycin concentrates within neutrophils and monocytes. 8,9 Whether this intracellular accumulation involves an active, saturable transport process has been studied in in vitro cell culture systems. In human fibroblasts and mouse macrophages, the entry of drug into the cell is rapid, and the intracellular concentration is proportional to both time of incubation and extracellular concentration (Figure 2).…”

Hyperactivity of cathepsin B and other lysosomal enzymes in fibroblasts exposed to azithromycin, a dicationic macrolide antibiotic with exceptional tissue accumulation

“…Azithromycin is a dicationic derivative of erythromycin A [1,2] which avidly accumulates in tissues [3,4] and in cultured mammalian cells, reaching intracellular to extracellular concentrations ratios of 100 and more [5]. Cell fractionation studies show that the bulk of the drug accumulated by cells localizes in the lysosomes [6].…”