According to one definition, the heavy metals are a group of elements between copper and lead on the periodic table of the elements—having atomic weights between 63.546 and 200.590 and specific gravities greater than 4.0. Living organisms require trace amounts of some heavy metals, including cobalt, copper, manganese, molybdenum, vanadium, strontium, and zinc, but excessive levels can be detrimental to the organism. Other heavy metals such as mercury, lead and cadmium have no known vital or beneficial effect on organisms, and their accumulation over time in the bodies of mammals can cause serious illness.

A stricter definition restricts the term to those metals heavier than the rare earth metals, at the bottom of the periodic table. None of these are essential elements in biological systems; all of the more well-known elements with the exception of bismuth and gold are horribly toxic. Thorium and uranium are sometimes included as well, but they are more often called simply "radioactive metals".

In medical usage, the definition is considerably looser, and "heavy metal poisoning" can include excessive amounts of iron, manganese, aluminium, or beryllium (the second-lightest metal) as well as the true heavy metals.

Also, often the elements beyond mercury, e.g., the actinides such as uranium and plutonium, are not excluded from the heavy metals. In the context of nuclear power plants, tHM means tons of heavy metal.

Definition

Chelation therapy is the administration of a drug that draws toxic metals from the bloodstream so that the body can pass them more effectively in urine or feces.

Purpose

Physicians have used chelation therapy since the 1950s to treat heavy metal poisoning--primarily lead poisoning--and to remove metals that have built up in tissues as a result of such genetic disorders as Wilson's disease, cystinuria, and hemochromatosis. Chelation therapy is generally only recommmended when high levels of metal are present in the blood, since it does not seem to benefit those with lower levels. In the case of heavy metal poisoning, removing the patient from the toxic environment is as important for successful recovery as chelation therapy. In addition to these accepted uses, chelation therapy has also been promoted by some as a non-surgical alternative for the treatment of cardiovascular disease. Advocates assert that chelation therapy can break up the plaque that obstructs arteries and reverse the clogging symptoms of atherosclerosis. However, no controlled scientific study has yet supported these claims and most physicians do not recommend chelation therapy for this purpose.

Description

Currently, four drugs are used for chelation therapy: edetate calcium disodium (calcium EDTA), dimercaprol (BAL), succimer, and d-Penicillamine. Calcium EDTA usually is injected into a muscle, but it can be administered through a vein. BAL is injected into a muscle and is usually used along with calcium EDTA for the treament of lead poisoning. Because the muscular injection of these two drugs can be painful, they are normally administered with a local anesthetic. Succimer and d-Penicillamine are given in pill form. Chelation therapy usually takes place in a hospital; however, the drugs can be administered on an out-patient basis.

Recommended dosage

Recommended dosage varies depending upon which drug is being used, the type and level of metal present in the patient's blood, and the patient's age and general health. If calcium EDTA is given on its own or with BAL, one treatment will last approximately five days with doses being given 4-12 hours apart. A second treatment may be administered after a two-day interval. If BAL is being given on its own, treatment will last approximately two weeks with doses being given 4-12 hours apart. Treatment with succimer will last approximately 19 days, while treament with d-Penicillamine may last as long as six months, particularly if the drug is being used to remove heavy metals that have accumulated in the blood because of a genetic disorder.

Precautions

Precautions regarding chelation therapy depend on which drug is being used. Patients who are pregnant or who have severe kidney problems, very low urine output, or very low blood circulation should not be given edetate calcium disodium (calcium EDTA). Patients with abnormally low levels of the enzyme glucose-6-phosphate dehydrogenase should not be given BAL, since the drug can trigger a breakdown of the red blood cells (hemolysis) in these persons. BAL should also not be given to patients who are allergic to peanuts, since the drug is mixed with peanut oil before it is administered. Finally, patients who are allergic to penicillin should not be given d-Penicillamine.

Side effects

High doses of calcium EDTA can cause kidney damage. However, this can be reversed when the patient stops taking the drug. High doses may also cause headache, fever, chills, nausea, and vomiting. An irregular heartbeat may also be experienced when this drug is rapidly injected into a vein. Treament with BAL may produce a mild fever, nausea with occasional vomiting, and an increase in liver enzymes. It also triggers a release of histamine in the body so the patient will likely experience allergy-like symptoms, such as a runny nose and watery eyes, which can be alleviated by antihistamines. Succimer can produce mild nausea, fever, chills, and a skin rash. D-Penicillamine can cause an allergic reaction, particularly in persons with a sensitivity to penicillin.

Interactions

Iron supplements should not be taken while BAL is being administered, since the interaction between the two can cause severe vomiting.

Key Terms

Atherosclerosis: A disease of the arteries marked by the deposit of fatty-fibrous plaque.
Chelate: A chemical substance that binds itself to another substance.
Cystinuria: An rare inherited defect of the kidneys in which the amino acid cystine is not properly transported and is therefore excreted into the urinary tract, where it often forms cystine stones.
Hemochromatosis: A rare hereditary disorder in which the body absorbs too much iron.
Wilson's disease: A rare hereditary disorder in which excess copper accumulates in the liver and other tissues.

For Your Information

Periodicals

Bennett, Dawn D. "Chelation Therapists: Charlatans or Saviors?" Science News (March 2, 1985): 138-139.
Ferguson, Tom. "Medical Self-Care: The Chelation Controversy." The Mother Earth News (March/April 1986): 110-112.
Goyer, R. A., et. al. "Role of Chelating Agents for Prevention, Intervention, and Treatment of Exposures to Toxic Metals." Environmental Health Perspectives (November 1995).
Null, Gary. "Chelation Therapy: One of Medicine's Best-Kept Secrets?" OMNI (November 1993): 18-20.
Other
American Academy of Pediatrics. "Treatment Guidelines for Lead Exposure in Children (RE9529)." http://www.aap.org/policy/00868.html.

Gale Encyclopedia of Medicine. Gale Research, 1999.

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