No abstract

Pefloxacin, like other fluoroquinolones, accumulates in macrophages and several other types of nucleated cells (but not in erythrocytes). Upon fractionation of macrophage homogenates by isopycnic centrifugation in sucrose gradients, fluoroquinolones are not found associated with any specific cellular structure. We have compared the activities of pefloxacin and roxithromycin against intracellular Staphylococcus aureus in mouse J774 macrophages. Pefloxacin was significantly more active for equivalent intracellular drug concentrations (i.e. expressed by reference to the respective MICs of the drugs as determined in broth), suggesting differences in intracellular availability and/or capacity of the drugs to express their activity in the intracellular environment. The difference was enhanced by incubating the cells in acidic medium. We have also examined the cellular pharmacokinetics and intracellular distribution of pefloxacin in uninfected and Legionella pneumophila infected guinea pig macrophages. In contrast to uninfected cells from which pefloxacin was quickly released, macrophages infected with legionella retained approximately 20-30% of the accumulated pefloxacin after a 60-min wash-out. Cell fractionation studies indicated that the drug remaining in cells was associated with components of high buoyant density. These fractions also contained [3H] if cells had been incubated with [3H] labelled legionella (by in-vitro exposure to [3H]-thymidine, before phagocytosis). These results suggest that part of the intracellular pefloxacin becomes associated with legionella, or with legionella-containing cytoplasmic structures.

The intracellular accumulation and subcellular distribution of 14C-labelled roxithromycin and erythromycin has been studied in macrophages and polymorphonuclear neutrophils of both human and animal origin. Roxithromycin was consistently and significantly more accumulated than erythromycin, reaching intracellular/extracellular concentration ratios between 14 (in polymorphonuclear neutrophils) and 190 (in alveolar macrophages from smokers). Uptake was reversible, insensitive to anaerobiosis and to the presence of an aminoglycoside, but inhibited by acid pH. Upon subcellular fractionation by isopycnic centrifugation in sucrose gradients., half the roxithromycin or erythromycin recovered in cell homogenates was found associated with the lysosomes in macrophages, and about one third with azurophil granules in polymorphonuclear leucocytes. Inasmuch as cellular uptake is a necessary, albeit not sufficient, condition for antimicrobials to kill or inhibit the growth of intracellular bacteria the properties of roxithromycin may give it a distinct advantage over other antimicrobial agents.

The recovery from gentamicin-induced phospholipidosis in the rat kidney cortex was characterized both morphologically and biochemically after a single 12-hr drug infusion. Total dosages administered were 10, 60, or 140 mg/kg, achieving constant serum concentrations of 3, 11, and 27 micrograms/ml, respectively. At the end of the 12-hr infusion, the cortical drug concentrations corresponding to the three dosages were 124, 450, and 993 micrograms/g of wet tissue. At the low dose (10 mg/kg), myeloid bodies were seen inside lysosomes of proximal tubular cells, along with a modest decrease of lysosomal sphingomyelinase activity. The cortical drug level declined steadily following first-order kinetics along with a disappearance of myeloid bodies and return of sphingomyelinase activity to control levels. At the high dose (140 mg/kg), we observed a sustained loss of sphingomyelinase activity (37% of controls), a subsequent increase of phospholipid concentration in the kidney cortex (up to 117% of controls 2 days after) and a prominent accumulation of myeloid bodies inside the lysosomes of proximal tubular cells (up to 4% of cell volume). Tubular regeneration and interstitial infiltration became detectable by histology and the increase of DNA synthesis as from day 1, along with an apparent reduction of the phospholipidosis at days 3 and 4. Drug cortical concentrations showed a sharp decline 2 days after infusion. An intermediate behavior was observed at 60 mg/kg. It is concluded that the proximal tubular cells behave in a fundamentally different way after gentamicin loading with low and high doses. At the low dose there is a regression of the drug-induced changes in the absence of any sign of necrosis-regeneration. Above a threshold in cortical drug concentration there is further development of the alterations leading to cell death-regeneration.