Remedy against radioactive poisoning (Ca-DTPA versus Zn-DTPA)

The authors report on recent investigations of the problem of radioactive decorporation. At present, Ca-DTPA is regarded as the substance of choice. Extensive animal experiments have proved its advantage over Ca-EDTA. However, Ca-DTPA also has toxic side-effects when given in high doses. When investigating the causes of this toxicity, the authors found that Ca-DTPA increases the renal Mn and Zn excretion, thus causing an inhibition of certain enzymes, including DNA-synthesizing enzymes. It has been tried to avoid this effect by administering Zn-DTPA instead. Zn-DTPA was indeed better tolerated and less toxic, but it was also less effective with regard to decorporation when given in the early stages. At a later stage, the efficiency of the two chelates is about the same. 10 month's long-term treatment of rats with Ca- and Zn-DTPA according to a treatment scheme also used in human medicine did not indicate any toxic effects. It is therefore recommended to use Ca-DTPA for early treatment while Ca-DTPA or Zn-DTPA may be used at will in the later stages. Zn-DTPA is recommended for long-term therapy. (MG)