Biliary and urinary excretion of iopanoic acid in the dog.

The urinary and biliary excretion of iopanonic acid was studied in anesthetized dogs infused with sodium iopanoate and trace amounts of 125I-iopanoic acid to provide a wide range of plasma concentrations. Samples of kidney and liver were also analyzed for total radioactivity. The sole excretory product in urine and bile was the glucuronide conjugate. The secretory biliary Tm for for iopanoic acid varied between experiments. Biliary concentration far exceeded that of plasma and liver/plasma ratios were all greater than unity. The fractional rate of urinary excretion varied 1-80% and was strongly correlated with hepatic function, e.g. the rate of bile flow. The data are interpreted to indicate that, depending on the rate of bile flow, the glucuronide formed in the liver is partioned between bile and blood, the latter for urinary excretion. This mechanism is discussed in relation to cholecystographic visualization and to the problem of nephrotoxicity.