Comparison of Fe-HBED and Fe-EHPG as hepatobiliary MR contrast agents

The authors studied the biodisposition and hepatobiliary transport of two potential magnetic resonance imaging contrast agents, the iron (III) chelates of N,N'-bis(2-hydroxybenzyl)ethylene-diamine-N,N'-diacetic acid (HBED) and diastereomeric N,N'-ethylenebis(2-hydroxyphenylglycine) (EHPG). Fecal and urinary excretion (mean +/- standard deviation), respectively, of FE-59 over 7 days in rats given tracer doses of the contrast agents were 67% +/- 2% and 22% +/- 1% for Fe-59-HBED and 22% +/- 2% and 26% +/- 5% for Fe-59-EHPG. In bile duct-cannulated rats given 0.05-mmol/kg doses labeled with Fe-59, 52% +/- 8% of Fe-59 from Fe-59-HBED but only 17% +/- 3% of that from Fe-59-EHPG was excreted into the bile within 90 minutes. Bromosulfophthalein, but not taurocholate or oxyphenonium, was shown to compete with both agents for hepatobiliary transport. Enterohepatic recirculation of both agents was less than 1%.