The role of some pharmacokinetic factors in the biliary excretion of exogenous organic anions.

The role of plasma and liver concentrations of exogenous organic anions and the significance of biotransformation of bromsulfphthalein (BSP) in the biliary excretion rate have been studied in male Sprague-Dawley rats weighing 200-250 g. No parallelism was found between plasma concentration and liver concentration after administration of the same dose of drugs to bile duct-ligated rats. A comparison of the values of hepatic concentration with the biliary excretion rate of drugs seemed to show a negative correlation between these parameters. Biotransformation of BSP (conjugation with glutathione) plays an important role in the biliary excretion of this drug, because the pharmacokinetic parameters of conjugated BSP are quite different from those of unconjugated BSP.