The penetration and intracellular activity of an antimicrobial agent is particularly important in conditions where the infecting microorganism is able to survive and multiply within phagocytic cells. Basically, four different methods can be applied for measuring antimicrobial uptake by phagocytes: bioassay, radiometry, high-performance liquid chromatography (HPLC) and fluorimetry. Controversial results are commonly found and related to methodological and experimental conditions. Regardless of the methodology used, beta-lactams seem to penetrate but not to accumulate within human phagocytes and show no intracellular activity. Aminoglycosides penetrate rather poorly but show some intracellular activity after long incubation periods. Lincosamides and macrolides reach high intracellular concentrations, but existing data about their intracellular activity are controversial. The azalide azithromycin accumulates intracellularly in different phagocytic and non-phagocytic cells, showing bacteriostatic activity against intracellular Staphylococcus aureus and high bactericidal activity against Haemophilus influenzae. All the fluoroquinolones evaluated have shown a good correlation between their high intracellular penetration and activity against different pathogens. Similar findings have been described for rifampin. Glycopeptide antimicrobials fail to concentrate intracellularly in human phagocytes. It is important to evaluate the intracellular penetration, subcellular distribution and activity of new antimicrobial agents in order to find out their potential use in infections caused by bacteria able to survive intracellularly.
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Álvaro Pascual (1995) studied this question.