The inhibitory effect of fluconazole (FCZ), a bis-triazole antimycotic, on mouse hepatic microsomal cytochrome P-450-mediated drug-metabolizing enzyme system was compared with those of ketoconazole (KCZ) in vivo and in vitro. Additionally, the change in the hepatic oxidative drug-metabolizing capacity in humans treated with FCZ was followed. The pentobarbital sleeping time in mice given a single dose of 1-10 mg/kg of FCZ or 30-50 mg/kg of KCZ was prolonged significantly, and the potency of FCZ for the prolongation of sleeping time was greater than that of KCZ. In contrast, in vitro the affinity and the inhibitory potency of FCZ for cytochrome P-450 and aminopyrine N-demethylation were 4- to 6-fold smaller than those of KCZ. However, the order of the inhibitory potencies among antimycotics for this enzyme systems in vitro was reversed by the addition of albumin into the reaction mixture. These results indicate that the difference in the plasma protein binding properties between FCZ and KCZ is an important factor which leads to a reverse in the order of their inhibitory potencies for this enzyme system in vitro and in vivo. The ratio of 6-beta-hydroxycortisol (6 beta-OHF) to cortisol (F) in urine, used as an indicator of oxidative drug-metabolizing capacity in humans, decreased to 50% of the original level during treatment with 200 mg/d of FCZ.(ABSTRACT TRUNCATED AT 250 WORDS)

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To further the understanding of the complexity of cyclosporin A (CyA) pharmacokinetics, we conducted an erythrocyte uptake and efflux study, and a protein binding study in human blood. The uptake study showed that the transport of CyA from the extracellular fraction to erythrocytes was retarded by increased human serum albumin (HSA) and lipid levels in this fraction. In addition, the concentration of CyA in erythrocytes increased with increases in CyA concentration in blood and reductions in hematocrit. The efflux study showed that the transport of CyA from erythrocytes to the extracellular fraction was essentially enhanced by increases of HSA and lipid levels in that fraction, but that these effects were relatively small. There were two affinity binding sites for CyA in ghost-free erythrocyte hemolysate, but not in the plasma fraction. The affinity binding constants for these binding sites were reduced by elevations in temperature, and under physiological conditions, 37 degrees C, almost all the CyA in erythrocytes was bound to a CyA binding protein, namely, cyclophillin. These findings suggest that CyA distribution in blood is of two different types which are present in the erythrocyte and plasma fractions, respectively. Monitoring of blood biochemistry variables showed that the concentration of CyA in erythrocytes had an interlocking relationship with these physiological factors, which were related to patient disease state, i.e., hematocrit, lipids, albumin, and total protein; the concentration of CyA in erythrocytes could be predicted from these physiological factors.

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