2.1 Dose

Administer Ca-DTPA as the initial dose during the first 24 hours after internal contamination. Ca-DTPA is more effective than Zn-DTPA during this time period. If Ca-DTPA is not available, use Zn-DTPA as the initial therapy. On the next day, if additional chelation therapy is indicated, begin daily treatment with Zn-DTPA (see Zn-DTPA labeling). If Zn-DTPA is not available, chelation therapy may continue with Ca-DTPA; concomitant mineral supplements containing zinc should be given. [See Warnings and Precautions (5.2)]

Do not administer more than one dose per 24 hour period.

2.2 General

Chelation treatment is most effective if administered within the first 24 hours after internal contamination. Start chelation treatment as soon as possible after suspected or known internal contamination. When treatment cannot be started right away, give chelation treatment as soon as it becomes available. Chelation treatment is still effective even after time has elapsed following internal contamination. The chelating effects of Ca-DTPA are greatest when radiocontaminants are still circulating or are in interstitial fluids. The effectiveness of chelation decreases with time following internal contamination as the radiocontaminants become sequestered in liver and bone.

If internal contamination with radiocontaminants other than plutonium, americium, or curium, or unknown radiocontaminants is suspected, additional therapies may be needed (e.g., Prussian blue, potassium iodide).

2.3 Methods of Administration

Use intravenous administration of Ca-DTPA if the route of internal contamination is not known or if multiple routes of internal contamination are likely. Administer Ca-DTPA solution (1 gram in 5 mL) either with a slow intravenous push over a period of 3-4 minutes or by intravenous infusion diluted in 100-250 mL of 5% dextrose in water (D5W), Ringers Lactate, or Normal Saline.

In individuals whose internal contamination is only by inhalation within the preceding 24 hours, Ca-DTPA can be administered by nebulized inhalation as an alternative route of administration. Dilute Ca-DTPA for nebulization at a 1:1 ratio with sterile water or saline. After nebulization, encourage patients to avoid swallowing any expectorant. Some individuals may experience respiratory adverse events after inhalation therapy. [See Warnings and Precautions (5.1)]

The safety and effectiveness of the nebulized route of administration have not been established in the pediatric population.

The safety and effectiveness of the intramuscular route of injection have not been established. [See Overdosage (10)]

2.4 Monitoring

When possible, obtain baseline blood and urine samples (CBC with differential, serum creatinine, BUN and electrolytes, urinalysis, and blood and urine radioassays) before initiating treatment.

Ca-DTPA must be given with very careful monitoring of serum zinc and complete blood counts. When appropriate, administer vitamin or mineral supplements that contain zinc. [See Warnings and Precautions (5.2)]

To establish an elimination curve, obtain a quantitative baseline estimate of the total internalized transuranium element(s) and measures of elimination of radioactivity by appropriate whole-body counting, by bioassay (e.g., biodosimetry), or fecal/urine sample whenever possible.

5.1 Asthma Exacerbation

Nebulized Ca-DTPA is associated with asthma exacerbation. Monitor patients for signs and symptoms of asthma exacerbation when administering Ca-DTPA by the inhalation route. [See Adverse Reactions (6)]

5.2 Depletion of Body Trace Mineral Stores

Ca-DTPA is associated with depletion of endogenous trace metals (e.g., zinc, magnesium, manganese). The magnitude of depletion increases with split daily dosing, with increasing dose, and with increased treatment duration. [See Clinical Pharmacology (12.3)] Only a single initial dose of Ca-DTPA is recommended. Use Zn-DTPA if additional chelation therapy is indicated (See Zn-DTPA labeling). If Zn-DTPA is not available, chelation therapy may continue with Ca-DTPA but give mineral supplements containing zinc concomitantly, as appropriate.

Monitor serum zinc levels, electrolytes and blood cell counts during Ca-DTPA or Zn-DTPA therapy. Give mineral or vitamin plus mineral supplements that contain zinc as appropriate. [See Dosage and Administration (2.4)]

5.3 Risks to Care-takers

Radioactive metals are known to be excreted in the urine, feces, and breast milk. In individuals with recent internal contamination with plutonium, americium, or curium, Ca-DTPA treatment increases excretion of radioactivity in the urine. Take appropriate safety measures to minimize contamination of others. [See Patient Counseling Information (17)]

5.4 Risks for Patients with Hemochromatosis

Use of only a single Ca-DTPA dose is particularly important for patients with hemochromatosis. Deaths have been reported in patients with severe hemochromatosis who received Ca-DTPA for more than 1 day, by intramuscular injection. [See Overdosage (10)]

8.1 Pregnancy

8.3 Nursing mothers

It is not known whether Ca-DTPA is excreted in human milk. Radiocontaminants are known to be excreted in breast milk. Women with known or suspected internal contamination with radiocontaminants should not breast feed, whether or not they are receiving chelation therapy. Precautions should be taken when discarding breast milk. [See Warnings and Precautions (5.3)]

8.4 Pediatric use

The safety and effectiveness of Ca-DTPA were established in the adult population and efficacy was extrapolated to the pediatric population for the intravenous route based on the comparability of pathophysiologic mechanisms. The dose is based on body size adjustment for an intravenous drug that is renally cleared [See Dosage and Administration (2.1)]. The safety and effectiveness of the nebulized route of administration have not been established in the pediatric population.

12.1 Mechanism of Action

Ca-DTPA forms stable chelates with metal ions by exchanging calcium for a metal of greater binding capacity. The radioactive chelates are then excreted by glomerular filtration into the urine. In animal studies, Ca-DTPA forms less stable chelates with uranium and neptunium in vivo resulting in the deposition of these elements in tissues including the bone. Ca-DTPA treatments are not expected to be effective for uranium and neptunium. Radioactive iodine is not bound by DTPA.

12.2 Pharmacodynamics

In a study of rodents internally contaminated with plutonium, the rate of plutonium elimination was measured after treatment with Ca-DTPA and Zn-DTPA given intravenously as a single dose of 10 to 1,000 micromol/kg (0.54-54 × maximum human dose, MHD). When treated within one hour of internal contamination, Ca-DTPA resulted in about a 10-fold higher rate of elimination of plutonium in the urine as compared to Zn-DTPA. The chelating capacity of Ca-DTPA is greatest immediately and up to approximately 24 hours after internal contamination, a time period when the radiocontaminant is still circulating and readily available for chelation. After the first dose of Ca-DTPA, maintenance treatment with either Ca-DTPA or Zn-DTPA resulted in similar rates of elimination of radioactivity. However, at comparable doses, Ca-DTPA had more toxicity (e.g., more depletion of trace metals, higher rate of mortality, the presence of kidney and liver vacuolization, and small bowel hemorrhagic lesions).

In another study, rodents contaminated with aerosolized plutonium and americium were treated with Ca-DTPA and Zn-DTPA. The treatment schedule involved inhalation of Ca-DTPA 2 micromol/kg (0.11 MHD) 30 minutes after contamination followed by inhalation of Zn-DTPA 2 micromol/kg at approximately 6 hours, 1, 2, 3, and 6 days, then twice weekly to day 26 or day 27. The treatment regime reduced the lung deposit of plutonium and americium to 1-2% of that in untreated animals. Systemic deposit in liver and skeleton were reduced by half.

Literature and U.S. Registry data in humans indicate that intravenous administration of Ca-DTPA forms chelates with radioactive contaminants found in the circulation, interstitial fluid, and tissues. When Ca-DTPA is administered by inhalation within 24 hours of internal radioactive contamination, it can chelate transuranium elements. Expectoration is expected to decrease the amount of radioactive contaminant available for systemic absorption.

The effectiveness of chelation decreases with time after internal contamination because the transuranium elements become incorporated into the tissues. Give chelation treatment as soon as possible after known or suspected internal contamination with transuranium elements has occurred. [See Dosage and Administration (2.1, 2.2)]

12.3 Pharmacokinetics

Plasma retention and urinary excretion data were obtained in 2 subjects that received 750 kBq of 14C-DTPA. As shown in Figure 1, the radiolabeled DTPA was rapidly distributed throughout the extracellular fluid space and was cleared by glomerular filtration. The plasma retention up to 7 hours post dosing was expressed by the sum of three exponential components with average half-lives of 1.4 min, 14.5 min, and 94.4 min. The level of activity in the plasma was below the limit of detection 24 hours after injection. During the study, no detectable activity was exhaled or excreted in the feces. By 24 hours, cumulative urinary excretion was more than 99% of the injected dose.

Figure 1: Percent of 14C-DTPA Distribution

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Studies with Ca-DTPA to evaluate carcinogenesis, mutagenesis, and impairment of fertility have not been performed. Data for Ca-DTPA effects on spermatogenesis are not available.

13.2 Animal Toxicology and/or Pharmacology

[See Clinical Pharmacology (12)]

16.2 Storage

Store between 15-30°C (59-86°F).

16.3 Handling

Inspect parenteral drug products visually for particulate matter and discoloration prior to administration, whenever solution and container permit. The product may be filtered using a sterile filter if particles are seen subsequent to opening of the ampoule.

OPC ampoule: to open, turn so that the point faces upward and break off the neck with a downward movement.