Lysosomal alterations induced in cultured rat fibroblasts by long-term exposure to low concentrations of azithromycin.

Computer-aided simulations suggest that the doses and schedules of administration of azithromycin proposed in treatment and prophylaxis of Mycobacterium avium complex (MAC) in AIDS patients will result in drug concentrations in serum and extracellular fluids remaining for sustained periods of time in the 0.03-0.1 mg/L range. We exposed cultured rat embryo fibroblasts to these concentrations (and multiples up to 20 mg/L) for up to 16 days. Electron microscopy showed that after 7 days' incubation in 0.03 mg/L azithromycin, there was conspicuous accumulation of osmiophilic, lamellar structures (myeloid bodies) in lysosomes, suggesting the onset of a phospholipidosis. Assay of total cell phospholipids and cholesterol showed significant increases in cells exposed to > or = 1 to 5 mg/L of azithromycin in association with hyperactivity of the lysosomal enzyme cathepsin B. The data suggest that azithromycin, at extracellular concentrations pertinent to its use for MAC treatment, and perhaps also prophylaxis, causes limited morphological alterations of the lysosomes in cultured cells which are of the same nature as those developing rapidly and extensively at higher concentrations.