If the contamination route is mixed or unknown, then Ca-DTPA should be administered intravenously. The intravenous dose of Ca-DTPA is 1 g in adults and 14 mg/kg up to the adult dose in children under 12 years up to a maximum of 1 g, administered either undiluted over 3 to 4 minutes, or diluted in 100 to 250 mL D5W, Ringer lactate, or 0.9% sodium chloride, over 30 minutes. On the basis of animal studies, it should not be given more slowly.4 Maintaining normal volume status and frequent voiding should be encouraged to dilute the radioactive chelate and minimize exposure to the bladder. If contamination occurred only via inhalation, then Zn-DTPA may be diluted 1:1 with sterile water or 0.9% sodium chloride and administered via nebulization.16
Although Ca-DTPA is recommended as the initial chelator, Zn-DTPA should be used after the first 24 hours. Although animal studies show a 10 fold increased rate of elimination of Pu with Ca-DTPA compared with Zn-DTPA, trace metals, such as zinc, are excessively removed with continued treatment with Ca-DTPA. After this period, Zn-DTPA given daily at the same dose is recommended for any continuing therapy because of its relatively diminished depletion of trace metals and the absence of liver, kidney, and intestinal injury.
Timing of Administration and Duration of Therapy
Administration of DTPA is recommended to begin as soon as possible, preferably within the first hour following contamination. Historically, about 55% of all patients treated with DTPA required only one dose. The decision to continue therapy should be based on radioassay data. This assessment should include collection of 24-hour urine samples, whole body or chest counting, and close consultation with the hospital radiation safety officer. Assistance is also available from REAC/TS at 865-576–1005; ask for REAC/TS. Current recommendations are to continue chelation until the deposition of contaminant is less than 5% of the maximum permissible body burden for a given contaminant.3
If continued therapy is indicated, then a regimen of Zn-DTPA may begin the day following initiation of therapy. Dosing regimens may include Zn-DTPA 1 g intravenously daily up to 5 days per week for the first week. If continuing chelation therapy is indicated, then a twice a week regimen should be initiated until the excretion rate of the contaminant does not increase with Zn-DTPA administration.15,16 As with the decision to initiate DTPA therapy, any continued treatment must be coordinated with a radiation safety officer. For all patients, data regarding vital signs, adverse effects, and bioassay studies should be reported to the drug manufacturer and also to REAC/TS.
A complete blood count with differential, blood urea nitrogen, serum chemistries and electrolytes, urinalysis, as well as blood and urine radioassays should be obtained prior to initiating treatment. Daily zinc, manganese, and magnesium monitoring should occur as well as supplementation with zinc. During treatment, repeated blood, urine, and fecal radioassays should be run to monitor elimination.
Patients with Chronic Kidney Disease
Although dose adjustment is currently recommended for patients with chronic kidney disease, kidney disease will impair chelate elimination from the body. Hemodialysis might be used to increase the rate of chelate elimination in these patients. Since dialyzed radionuclides will contaminate dialysis fluid, care must be exercised during the procedure as well as in discarding fluid and preparing the machine for subsequent patient use. Consultation with the radiation safety officer (RSO) is recommended to assist with discarding waste material, as well as with the overall chelation treatment of the contaminated patient.