Inhibition of intracellular growth of Staphylococcus aureus by exposure of infected human monocytes to clarithromycin and azithromycin.

The direct effect of clarithromycin and azithromycin on human polymorphonuclear leukocyte (PMN) functions and their intracellular activity against Staphylococcus aureus, phagocytosed by human monocytes, were studied. The presence of both antibiotics, in the range of concentrations from 0.25 to 20 micrograms/ml, did not affect chemotaxis, opsonized-zymosan phagocytosis, respiratory burst measured by nitroblue tetrazolium reduction and phorbol myristate acetate-induced superoxide production, or the microbicidal activity of human PMNs against Candida albicans. Both macrolides were bactericidal against staphylococci in the monocyte system, while bacteriostatic activity was found in cell free system. At concentrations equal to the minimum inhibitory concentrations (MICs) (0.75 and 0.1 respectively for azithromycin and clarithromycin) more than 99% of intraphagocytic S. aureus were killed after 24 h incubation. Increasing the concentrations of each drug above the MICs (5 and 10 MICs) did not alter the killing rate of intracellular bacteria. Moreover, no differences between the intracellular bioactivity of these antibiotics were demonstrated, despite their different uptake kinetics.

Requirements for intracellular accumulation and release of clarithromycin and azithromycin by human phagocytes.

Determination of clarithromycin (CL) and azithromycin (AZ) uptake by human polymorphonuclear leukocytes (PMNs), monocytes and alveolar macrophages showed that AZ achieved higher levels than CL. The uptake kinetics of AZ were time-dependent over an 18 h period, while those of CL were similar to erythromycin (ER) kinetics, with a maximum level of incorporation being obtained after a 60 min incubation. The accumulation of both drugs was influenced by extracellular antibiotic-concentrations, PMN viability, extracellular calcium, physiological environmental temperature and pH. The uptake was not modified by inhibitors of cell metabolism or activators of cell membranes. After removal of extracellular antibiotic, the release of AZ from PMNs was very slow: nearly 50% of the drug remained cell-associated after 24 h incubation. The efflux of this derivative was significantly enhanced when drug-loaded PMNs were stimulated by phorbol-myristate acetate (PMA). The kinetics of CL release indicated that this macrolide behaved like ER. Nevertheless, about 10% of the initial cell-associated antibiotic showed a prolonged retention. On the whole, these data suggest that diffusion through cell membranes and trapping into acidic compartments of PMNs are important events in CL and AZ uptake.

Evidence for CD8+ cell increase in long-term PUVA-treated psoriatic patients after PUVA discontinuation.

Long-term PUVA-treated psoriatic patients given maintenance therapy (UVA doses greater than 1,000 J/cm2) have been demonstrated to undergo lymphopenia and a decrease in the total number of circulating CD3+ and CD4+ T cells. The aim of this study was to assess whether the impairment of T cells is detectable also in psoriatic patients after long-lasting PUVA discontinuation. A group of 34 psoriatic patients (25 males, 9 females; mean age 52.7 +/- 12.82 years), who had previously been treated by PUVA therapy (average cumulative dose 1,898.48 +/- 1,207.12 J/cm2), was studied 1 year or more after discontinuation of PUVA therapy. The patients studied failed to show any impairment in CD3+ and CD4+ cells. Nevertheless, a significant increase (p less than 0.05) in circulating CD8+ cells (both in the percentage and the total number) was detectable in PUVA patients as compared to appropriate controls. The significance and implications of this finding are not known and need further investigations.