EMBARGOED BY JOURNAL Wednesday, May 9, 2001 5:00 p.m. EST
NIEHS contact: Bill Grigg (301) 402-3378
Drug Treatment of Lead-exposed Children Does Not Improve Psychological Test Scores ‘We must prevent exposure in the first place'
The Kennedy Krieger Institute in Baltimore, Md.,
The University of Cincinnati in Cincinnati, Ohio,
The University of Medicine and Dentistry of New Jersey, working with children in Newark, and Children's Hospital, Philadelphia, Pa.
The program was managed from NIEHS and the Harvard School of Public Health.
For the study, the Centers for Disease Control and Prevention measured blood lead and the Public Health Service Supply Service Center in Perry Point, Md., provided pharmacy services.
In the early 1990s, when the study was started, it was known that children exposed to more lead had lower scores on IQ tests and that succimer could lower lead levels in blood. It was not known whether using it prevented or reduced the effects of lead on test scores. About 780 children were enrolled between 1994 and 1997. Half were given succimer and half an identical capsule without active drug.
In addition, all the children's homes were cleaned of lead dust, they were given a mineral supplement, and their blood lead was followed. Detailed testing of their cognitive development, neuropsychological function, and behavior was done at three years of follow up. This is a time when the children are old enough to be given sophisticated tests (they were then about 5 years old) and it is the age at which there is the strongest evidence for an effect of lead.
While the children given succimer had more rapid drops in their blood lead, the differences in tests scores were small, inconsistent, and not statistically significant, the investigators said. The study was large enough to have detected an improved IQ score of less than 3 points, and no such improvement was seen.
Side effects were relatively infrequent in both groups, but the children given succimer had an unexpectedly higher rate of injuries, which is so far unexplained.
Based on these data, Rogan said, there is little reason to recommend chelation for children with exposures below the current recommendation of 45 mg/dL. Children generally have no symptoms below that level. Succimer remains the recommended therapy for outpatient treatment of children above that level.
The children who participated in TLC are being followed for an additional two years to see if some benefit emerges. In an Australian study, children whose blood leads fell faster without treatment when they were two years old had better IQ test scores when they were seven years old, and 7 year old children attend school and read and so can be tested more extensively.
Although lead poisoning in the US has declined dramatically since the removal of lead from gasoline, in 1998 about 8% of screened children still had blood lead levels that CDC defined as elevated, and about 1% of screened children had a blood lead level high enough to have been eligible for the TLC trial. Lead poisoning is concentrating now among poor children who are eligible for Medicaid and live in deteriorating, inner city housing.