Time and concentration dependent influence of dirithromycin on neutrophils oxidative burst.

Dirithromycin is a 14-membered macrolide antibiotic, well known to yield high intragranulocytic levels after several hour exposure. We chose therefore to investigate oxidative metabolism after prolonged incubation periods with neutrophils. Neutrophil generation of reactive oxygen species, represented by superoxide anion, was assessed after fMLP or Staphylococcus aureus-induced activation of the respiratory burst. Cellular uptake of the drug was assessed concurrently, in order to attempt a correlation with time-dependent modifications of the cellular oxidative status. For 1 hour exposure time, a pro-oxidant effect was reported for lower concentrations, achievable during therapeutic administration, whereas the highest ones promoted a potent anti-oxidant effect. After prolonged incubation times, the anti-oxidant effect alone was reported, with time-dependent modifications of IC50 values. These values could be correlated with intracellular accumulation of the drug. The anti-inflammatory activity reported here for high dirithromycin concentrations, could be nevertheless clinically relevant, since dirithromycin cellular uptake extends beyond 4 hours.