Whole body quantitative autoradiographic study of the biodistribution of iobitridol in rats

Iobitridol is a new nonionic low-osmolality contrast medium. During preclinical development of this agent, it was of interest to verify that it behaves like other urographic and angiographic contrast agents (i.e., as a tracer of extracellular fluid).

Male and female rats were imaged using a quantitative autoradiographic method after intravenous administration of iodine-125-labeled product at a dose of 300 mg iodine/kg.

The radioactivity was rapidly distributed with substantial uptake in the thyroid, kidneys, and skin after 10 minutes. The central nervous system showed no uptake. The radioactivity was rapidly eliminated (i.e., after 24 and 48 hours, only traces were found) except in the thyroid (because of free radiolabeled iodides present in small quantities in the administered solution). The considerable renal uptake after administration can be attributed to urinary excretion of the radioactivity (86% of the administered dose after 24 hours). Total elimination was achieved after 48 hours. No sex-related effects were observed.

The absence of a target organ, the abundant and rapid urinary elimination, and the absence of transfer across the blood-brain barrier suggest that iobitridol is a tracer of extracellular fluid.