Human comparative study of zinc and copper excretion via urine after administration of magnetic resonance imaging contrast agents

Purpose: To evaluate the in-vivo pharmacokinetics of magnetic resonance imaging (MRI) contrast agents, the excretion of zinc and copper via urine was studied for three gadolinium (Gd) chelate complexes. Materials and Methods: Urine samples were taken before, three hours, and six hours after intravenous administration of Gd-DTPA-BMA, Gd-DTPA, and Gd-DOTA at 0.2 ml/kg to five patients each who underwent contrast-enhanced MRI. Five patients who had non-contrast MRI were evaluated as controls. Urine was assayed for quantitative analysis of zinc and copper using atomic absorption analysis. Results: Gd-DTPA-BMA caused the highest increase in zinc excretion among the three agents, 1,795±1,273 μg at 3 hours and 985±434 μg at 3 to 6 hours. Gd-DOTA did not cause a significant increase in zinc excretion, 75±39 μg at 3 hours and 78±65 μg at 3 to 6 hours. Gd-DTPA caused a moderate increase in zinc excretion, 665±240 μg at 3 hours and 378±173 μg at 3 to 6 hours. Excretion of copper did not show a significant difference among the three agents. Conclusion: Gd-DOTA was found to be the most kinetically inert among the three agents tested. The difference in zinc excretion among the MR contrast agents is possibly related to in-vivo transmetallation of the Gd chelate complexes correlated with variable stability of the contrast agents. The large amount of excess ligands contained in some MR contrast agents was also considered to be responsible for the increase of urinary zinc excretion.