The penetration of rifampicin, pyrazinamide, and pyrazinoic acid into mouse macrophages

The degree of penetration of rifampicin, pyrazinamide, and its metabolite pyrazinoic acid in mouse macrophages was evaluated over a period of 24 h. Cell cultures were exposed to 14C-labeled drugs at concentrations corresponding to peak, trough, and intermediate serum concentrations observed in humans after administration of therapeutic doses. The study was carried out with dead, resident, and stimulated peritoneal macrophages. The results indicated that the 3 compounds penetrate macrophages rapidly. At the lower concentrations, uptake of the 3 drugs is practically complete. With increasing concentrations, the absolute amount in the intracellular compartment increased. Comparison of the degree of penetration of the 3 drugs into dead, resident, and stimulated macrophages seems to suggest that the process of transfer through the macrophage wall is of a passive nature and not related to the metabolic state of the cells. Analysis of the binding of the 3 drugs to intracellular proteins indicated that more binding sites are probably available for rifampicin than for the other 2 drugs.