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November 8, 2010
Lead Poisoning Treatment Less Effective for Mercury
A drug commonly used to treat lead poisoning is relatively ineffective at removing mercury from the blood. The finding provides insight into a compound currently being used as an alternative therapy for autism.
Mercury poisoning can be dangerous and even fatal. Children might be exposed to mercury from several sources, but the majority of exposure in the United States comes in the form of methylmercury, which is found in foods such as certain fish. Methylmecury is known to be toxic to fetuses. Thimerosal, a preservative once commonly used in vaccines, contains another form of mercury called ethylmercury.
Some people believe that mercury in vaccines and from other sources can affect development of the nervous system and contribute to autism. However, extensive research has found no conclusive evidence that any part of a vaccine or combination of vaccines causes autism. Even so, aside from some flu vaccines, mercury compounds have been reduced or eliminated from most routine childhood vaccines.
Although it's not approved by the U.S. Food and Drug Administration to reduce mercury, a drug called succimer is reportedly being used as an alternative therapy for autism. Succimer is a chelating agent—a substance that can bind particular ions and remove them from solution. Succimer has been shown to effectively remove lead from the body and is commonly used to treat lead poisoning.
A research team led by Dr. Walter Rogan at NIH’s National Institute of Environmental Health Sciences (NIEHS) sought to investigate whether succimer can also remove mercury from the blood. The team used blood samples and data from 767 children, aged 12 to 33 months, who participated in an earlier clinical trial of children who were treated for high blood levels of lead.
The research team measured mercury concentrations in blood samples collected prior to treatment, a week after beginning treatment with succimer or placebo, and again after 3 month-long courses of treatment. The study was funded by NIEHS, NIH's National Institute for Minority Health and Health Disparities (NIMHD) and the Centers for Disease Control and Prevention. The results appeared online on October 1, 2010, in the Journal of Pediatrics.
The researchers found that, after 1 week, succimer lowered blood concentrations of mercury by 8%. In contrast, it reduced blood lead concentration by 42%. After 5 months, those taking succimer had blood mercury concentrations about 20% lower than the control group. However, the therapy had only slowed the rate at which the children accumulated mercury.
"Succimer is effective for treating children with lead poisoning, but it does not work very well for mercury," Rogan says. "Although succimer may slow the increase in blood mercury concentrations, such small changes seem unlikely to produce any clinical benefit."