As a result, experts say the best strategy against lead poisoning continues to be prevention -- cleaning up sources of the heavy metal, primarily dust or chips of lead-based paint that pose a particular risk for children.
"It has long been our position that primary prevention is the answer to lead poisoning," says Eileen Quinn, deputy director of the Alliance to End Childhood Lead Poisoning, a Washington, D.C.-based advocacy group. "These children suffer permanent damage that thwarts their chance in life."
"We know that there are effects of lead at lower levels [of exposure]. This [study] underscores that the most important treatment is really to remove the exposure" from the home, says Dr. Dennis Kim, a lead expert at the Centers for Disease Control and Prevention (CDC). The findings appears in the May 10 issue of The New England Journal of Medicine.
Because of successful prevention efforts, lead exposure and rates of lead poisoning in the United States are waning. Yet an estimated 890,000 children suffer lead poisoning, defined as more than 10 micrograms of lead per deciliter of blood. The latest CDC figures show that 8 percent of low-income children and 1 percent of wealthy children have elevated blood lead levels.
Most contamination occurs in poor, inner-city housing. The ages of structures usually indicate their risks as a lead hazards. Nearly 22 percent of black children who live in homes built before 1946 have elevated blood lead levels, compared with only 1.5 percent of whites living in homes built later, Kim says.
"Lead is still a significant public health problem, and we should remember that although chelation therapy may not be effective , it won't do any good if the kid continues to be exposed," Kim says.
The American Academy of Pediatrics doesn't recommend chelation therapy, which strips lead from the blood, in children whose blood lead levels are less than 45 micrograms per deciliter. The academy has been concerned that some doctors prescribe oral chelation medication to children as "off-label" treatment, without knowing how well it works, or if it works at all.
Even in children with blood lead counts greater than 45 micrograms, chelation isn't clearly effective at reversing brain damage, says Dr. Walter Rogan, an epidemiologist at the National Institute of Environmental Health Sciences in Research Triangle Park, N.C., and lead author of the latest study. "But it probably reverses some of the abnormalities" and also eases the anemia caused by severe exposure to lead.
The study compared the chelation drug succimer with placebo therapy in 780 inner city children with blood levels between 20 and 44 micrograms per deciliter, well above the government's threshold for nerve damage. Roughly three-quarters of the children, who ranged in age from 12 months to 33 months and lived in dilapidated housing, were African-American.
To prevent continued contamination of the children during the study, the researchers took aggressive steps to remove the toxin from their homes, swabbing dusty surfaces, repairing broken windows, performing other minor carpentry and removing literally pounds of lead-containing dust from houses and apartments. "If these kids moved, we went and cleaned their new house," Rogan says.
Succimer puts a molecular cage around lead molecules (and other poisonous metals) and shuttles them out of the body in urine. It's given in 19- or 26-day courses. Many children must take more than one round of the drug, sprinkled over applesauce or other foods, but its odor, which researchers say is akin to stale gym socks, makes it hard to endure.
Succimer produced an immediate drop in blood lead levels of children in the study, cutting them 10 micrograms per deciliter right away and by 50 percent, on average, over six months. But its effects on behavior, intelligence and learning were no better than the placebo therapy, the researchers say.
Three years after treatment, children who took the drug had IQs one point lower, on average, than those who didn't get treatment, and their behavior appeared to be worse, too. While children in the chelation group had a small edge over those on placebo in scores of learning ability, the differences didn't pass statistical muster.
"We went in the right direction with lead, and there's not even a hint of difference. We have no choice but to prevent this exposure to begin with," Rogan says.
Chelation is expensive. Succimer, for example, costs several hundred dollars per course, and in-hospital therapy is even pricier. And it's a niche treatment, since fewer than 40,000 children have blood lead levels between 20 and 45 micrograms per deciliter, Rogan says. Its utility is ever-shrinking, too, because of lead poisoning's dwindling threat in this country, he says.
A spokesman for the U.S. Department of Housing and Urban Development says the agency plans to spend $100 million this year on two programs that directly or indirectly target lead and is asking Congress for a $10 million raise in next year's budget.
That does not include $4.4 billion in block grant money to states, some of which finds its way into lead abatement efforts.
The Clinton Administration last year launched a multi-agency effort to control lead poisoning by targeting lead paint. The goal of that program is to eliminate lead hazards by the year 2010.
What To Do
For more on succimer, which is marketed by McNeil Consumer Products Company of Fort Washington, Pa., visit the Children's Hospital of Philadelphia.
Check other HealthScout articles about lead poisoning.