BIODISTRIBUTION AND EXCRETION OF GD-153-LABELED GADOLINIUM ETHOXYBENZYL DIETHYLENETRIAMINE PENTAACETIC ACID FOLLOWING REPEATED INTRAVENOUS ADMINISTRATION TO RATS

Rationale and Objectives. We investigated the distribution of radioact ivity in tissues and organs and its disappearance following repeated i ntravenous (IV) administration of Gd-153-labeled gadolinium ethoxybenz yl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) to rats. Methods. A high total dose of 250 mu mol/kg is equivalent to 92.5 kBq per anim al on 5 consecutive days) was given to conscious rats by fast IV injec tion via a tail vein. The organ distribution and the body elimination into urine and feces were investigated at time points 3, 7, 14, and 21 days following the last injection; five animals were used at each tim e point. All samples were measured by gamma counting of Gd-153 over a 10-min period. Results. The radioactivity quickly disappeared from the body, mostly through feces. In the liver, no radioactivity could be d etected at 3 days postinjection. At 21 days postinjection, only 0.002% of the gadolinium injected was detected, the vast majority (approxima tely 95%) of which was found in the kidneys. Conclusion. After repeate d IV administration of a total dose of 250 mu mol/kg of Gd-153-labeled Gd-EOB-DPTA, the elimination from the body was found to be 99.998% co mplete. Only negligible long-term retention of radioactive gadolinium was observed despite the relatively high dose injected. No perceptible evidence for decomplexation of Gd-EOB-DTPA could be found.