Cellular pharmacokinetics of spiramycin in cultured macrophages

To gain a better understanding of the antibacterial and antiprotozoal activity of spiramycin as well as the characteristic conditions of cellular defence, we studied its accumulation and intracellular localization in cultured macrophages. Within two hours spiramycin in its active form is accumulated intracellularly by macrophages to a concentration 10 to 20 times that found in the extracellular medium; it is released slowly by the cells when they are incubated in antibiotic-free medium. After differential or isopycnic centrifugation, a bimodal localization of spiramycin was found; one part could be associated with the soluble cytosolic fraction and another with organelles sedimenting at a density of 1.17 g/ml, which represent part of the lysosomal population and perhaps the phagosomes.