DTPA is indicated and FDA approved for suspected contamination via inhalation, dermal, or wound exposure from plutonium, americium, and curium, with the goal of mitigating radionuclide incorporation and local tissue irradiation. Inhaled metals, such as might be experienced following an explosion, may be treated with nebulized DTPA. Depending on the chemistry of the metal (eg, uranium concentrates in renal tissue), this irradiation could possibly lead to development of a malignancy later in life. Chelation is indicated to increase elimination of the radionuclide and decrease cancer risk. This latter has only been demonstrated in animals. Increased urinary excretion of transuranic elements is a clinically meaningful endpoint for efficacy of DTPA. Administration of these chelators is not recommended following ingestion of americium, curium, or plutonium, because they will increase gastrointestinal absorption.
A report published by the Radiation Emergency Assistance Center/Training Site (REAC/TS) reviewed data from 685 transuranic element exposures, most of which were plutonium, curium, and americium. Most of these exposures (63.5%) were by inhalation, typically a breach of a confined area where workers access the radioactive material via arm-length gloves reaching into a protective box. Ages of the exposed ranged from 10 to 64 years of age. From the 18 patients with the most complete urine bioassay data, the average increase in urine elimination of radionuclide was 39 times the baseline rate after the first dose of DTPA.18 By 24 hours, postexposure soluble plutonium and americium are deposited in bone, theoretically rendering DTPA ineffective (in the absence of bone remodeling).7 Historic data concerning contaminated workers at nuclear materials production facilities, which included those who received both prolonged and delayed treatments, demonstrated greatly increased urinary excretion of radioactive material.1,9, 10, and 11,19,20
Other more limited data suggest that DTPA may also be effective in increasing urinary elimination following exposure to californium and berkelium, and some experts recommend DTPA for chelation of these elements. Animal data suggest the potential utility for chelating cobalt, einsteinium, lanthanum, nickel, promethium, scandium, strontium, ytterbium, and yttrium. Pentetic acid salts are not effective in removing antimony, beryllium, bismuth, gallium, lead, mercury, neptunium, niobium, platinum, thorium, or uranium.
DTPA is neither recommended nor approved for treating patients contaminated with uranium or neptunium for several reasons. DTPA mobilizes uranium from tissue stores but does not increase urinary elimination.5,14 Chelating incorporated neptunium is problematic because it forms very stable complexes with transferrin, making it very difficult to decorporate.6,13