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)ethylenediamine-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. Bromosulfophtha-lein, but not taurocbolate or oxyphenonium, was shown to compete with both agents for hepatobiliary transport. Enterohepatic recirculation of both agents was less than 1%.