Metabolism of urographic contrast media

The metabolism of ionic and nonionic contrast agents was examined in the rabbit and in humans by specific measurement of iodide present in urine at different time intervals after injection of high contrast medium doses. Interest was focused on the experimental model compound C-29, which was investigated using a 125I-labeled compound, permitting a study of iodide release and the appearance of other metabolites in serum, bile, and urine from rabbits. Large, quantitative, individual variations were found, but in most cases th urine collected from both rabbits and humans contained more iodide than had been injected. A mean of 0.07% of total injected iodine was found within three days after injection of the ionic contrast medium metrizoate. The results with rabbits indicated that this figure may increase to 1% using the nonionic media tested. Direct evidence of metabolism of C-29 was found in bile, where up to 35% of the total radioactivity present in the bile 4-6 hours after injection was identified as a metabolite.