Pentetic acid

Diethylene triamine pentaacetic acid (DTPA) is an organic compound consisting of a diethylenetriamine backbone modified with five carboxymethyl groups. The molecule can be viewed as an elongated version of EDTA. DTPA is used as its conjugate base, often undefined, which has a high affinity for metal cations. Upon complexation to lanthanide and actinide ions, DTPA exists as the pentaanionic form, i.e. all five carboxylic acid groups are deprotonated.

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Coordination chemistry

DTPA is the parent acid of a octadentate ligand, diethylene triamine pentaacetate. In some situations, all five acetate arms are not attached to the metal ion. It has been used to decontaminate humans who have been poisoned with plutonium, americium and other actinides. Upon formation of chelate complexes, these heavy metal ions are less readily unabsorb and are more readily eliminated in urine. It is normally used as the calcium or zinc salt. When given within the first day after internal contamination has occurred, Ca-DTPA is about 10 times more effective than Zn-DTPA at chelating plutonium, americium, and curium. After 24 hours have passed, Ca-DTPA and Zn-DTPA are equally effective in chelating these radioactive materials.^{[citation needed]} "Internal contamination" is jargon for the unintention injestion of radioactive materials. Most cases of internal contamination result from working with radioactive materials.

What DTPA cannot do

DTPA cannot bind all of the radioactive materials that might get into a person’s body after a radiological or nuclear event, such as a terrorist attack with a “dirty bomb.” This medicine cannot prevent radioactive materials from entering the body. DTPA cannot reverse the health effects caused by radioactive materials once these materials have entered the body.

How well does DTPA work?

Chelating agents work best when given shortly after radioactive materials or poisons have entered the body. The more quickly a radioactive material or poison is removed from the body, the fewer and less serious the health effects will be. After 24 hours, plutonium, americium, and curium are harder to chelate. However, DTPA can still work to remove these radioactive materials from the body several days or even weeks after a person has been internally contaminated. Who should get DTPA? Many people could be internally contaminated after a radiological or nuclear terrorist event. People contaminated with small amounts of radioactive materials might not need treatment with DTPA. Doctors and public health authorities will work together to decide who will likely benefit from DTPA treatment. • Infants (including breastfed infants) and children<12 years of age

Either Ca-DTPA or Zn-DTPA may be given to infants and children. The dosage of DTPA to be given should be based on the child’s size and weight. • Young adults and adults

Young adults and adults internally contaminated with plutonium, americium, or curium should receive Ca-DTPA if treated within the first 24 hours after contamination. After 24 hours, if additional treatment is needed, adults should receive Zn-DTPA. If Zn-DTPA is not available, patients may receive Ca-DTPA together with a vitamin and mineral supplement that contains zinc. • Pregnant women

Unless a pregnant woman has very high levels of internal contamination with plutonium, americium, or curium, treatment should begin and continue with Zn-DTPA. Ca-DTPA should be used in pregnant women only to treat very high levels of internal radioactive contamination. In this case, doctors and public health authorities may prescribe a single dose of Ca-DTPA, together with a vitamin and mineral supplement that contains zinc, as the first treatment. However, after the first dose of Ca-DTPA, treatment should continue 24 hours later with a daily dose of Zn-DTPA, as needed. • Breastfeeding women

Radioactive materials can—and do—get into breast milk. For this reason, CDC recommends that women with internal contamination stop breastfeeding and feed the child baby formula or other food if it is available. If breast milk is the only food available for an infant, nursing should continue. Breastfeeding women who are internally contaminated with plutonium, americium, or curium should be treated with DTPA. How should DTPA be given? Currently, DTPA is only available by injection and is not available in an oral (by mouth) form. DTPA may be injected directly into a vein in the arm or dripped into a vein from a bag (intravenously [IV]). Injection and IV drip are good ways of treating people a) who might have been internally contaminated by eating, drinking, or inhaling radioactive materials or b) who have contaminated wounds. Adults who have inhaled plutonium, americium, or curium can be treated with DTPA mist or spray that is breathed into the lungs. Inhaling DTPA might cause some people, especially those with asthma, to cough or wheeze. The safety and effectiveness of inhaled DTPA has not been shown in children. How often will I need to get DTPA? DTPA should be taken only as long as your doctor has determined you need it. In the past, most people who have needed treatment with DTPA have only needed one dose. However, internal contamination with very high levels of plutonium, americium, or curium may require treatment with DTPA every day for weeks or months. The length of treatment with DTPA will depend on a) the amount of radioactive material in your body and b) how well your body gets rid of the radioactive material. Doctors might collect samples of blood, urine, and feces during treatment with DTPA. These samples can tell the doctors how much radioactivity you are passing and how much remains in your body. Medical conditions that might make it harmful to receive DTPA There are no medical reasons why a person who is internally contaminated with plutonium, americium, or curium should not be treated with Ca-DTPA or Zn-DTPA. However, keep the following guidelines in mind: • Because radioactive materials chelated to DTPA are passed out of the body in the urine, DTPA must be used carefully in people whose kidneys do not function properly. • Ca-DTPA should be used carefully in people who have a disease called hemochromatosis. • Breathing treatments using DTPA may not be safe for some people with asthma. If a person with asthma requires treatment with DTPA, the drug should be injected.

• DTPA should not be used to treat people who are internally contaminated with the radioactive materials uranium or neptunium.

What are the possible risks and side effects of DTPA?

DTPA does not build up in the body or cause long-term health effects. People who are given repeat doses of Ca-DTPA within a short period of time may have nausea, vomiting, diarrhea, chills, fever, itching, and muscle cramps. Other side effects may include headache, lightheadedness, chest pain, and a metallic taste in the mouth. Ca-DTPA (and Zn-DTPA) can chelate certain important minerals that the body needs (zinc, magnesium, and manganese). For example, the body needs zinc to make red blood cells, white blood cells, and platelets. Therefore, DTPA treatment may interfere with the normal production of blood cells. As a precaution, patients receiving long-term treatment with DTPA should be given a vitamin and mineral supplement that contains zinc.

Availability of DTPA

DTPA is commercially available. In the U.S., the CDC has included both Ca-DTPA and Zn-DTPA in the Strategic National Stockpile, a collection of emergency medicines and medical supplies.

Uses

Since the 1960s, doctors have used DTPA as a chelating agent to treat internal contamination from radioactive materials such as americium, plutonium, californium, curium, and berkelium. Currently, DTPA is approved by the U.S. Food and Drug Administration (FDA) for chelation of only three radioactive materials: plutonium, americium, and curium. It is used as a soil extractant for available soil micronutrients like Zn,Fe,Cu and Mn at the pH of 7.3 with Calcium chloride and TEA. Furthermore, it is used as to chelate gadolinium to form a MRI contrast agent, such as Magnevist

More advice

It should not be taken by people with kidney disease or bone marrow depression, nor by children younger than 18 years old. If the lungs are contaminated by the inhalation of these radioactive materials, a DTPA spray or mist is used. Otherwise it can also be injected intravenously.

References

This article incorporates material from Facts about DTPA, a fact sheet produced by the United States Centers for Disease Control and Prevention.

FDA Press Release http://www.fda.gov/bbs/topics/news/2004/NEW01103.html

FDA Approval Letter http://www.fda.gov/cder/foi/appletter/2004/21749,21751ltr.pdf

National Library of Medicine http://www.remm.nlm.gov/dtpa.htm