The treatment of lead-exposed children (TLC) trial: design and recruitment for a study of the effect of oral chelation on growth and development in toddlers

Exposure to lead impairs cognitive development in young children, but the benefits of lowering blood lead pharmacologically are not clear. This report describes the design, recruitment, enrolment and baseline results of the Treatment of Lead-Exposed Children (TLC) trial, a randomised, multicentre, placebo-controlled, double-blind clinical trial of the effects of treating lead-exposed children with succimer, a drug that enhances urinary excretion of lead, on cognitive, behavioural and physical development. TLC clinical sites were in Baltimore, Cincinnati and Columbus, Newark and Philadelphia. Children were eligible for TLC if they were between 12 and 33 months of age, had a confirmed blood lead concentration between 20 and 44 mu g/dL and lived in a residence suitable for lead dust reduction. Randomised children received up to three 26-day courses of succimer or placebo, and were then followed for 3 years. The study can detect a three-point difference in full-scale IQ at 3-year follow-up. Statistical power for the other end points is more difficult to estimate. A total of 1854 children were evaluated and 780 children were randomised between August 1994 and January 1997. The mean age of randomised children was 24 months and mean blood lead level 26 mu g/dL. Three-quarters were African-American. Most children had poor, single mothers who had completed 12 or fewer years of school and who lived in older, poorly maintained residences.