Removal from the rat of internally deposited 241Am by long-term treatment with Ca and ZnDTPA

The removal from the rat of intravenously injected241 Am by repeated administration of Ca- or ZnDTPA has been studied. With a prompt treatment, the efficacy of ZnDTPA is lower than that of CaDTPA, whereas delayed therapy yields identical results for both chelates. DTPA efficacy diminishes in the course of chronic treatment, and the loss in the effect due to delayed initiation of the treatment cannot be compensated for by an increase in the total cumulative dose of DTPA. After intramuscular administration of241 Am prompt DTPA treatment is highly effective as it enhances the absorption of241 Am and prevents the build-up of a systemic body burden. The practical implications of the results are discussed.