Succimer unlikely to reduce blood mercury levels

Succimer, a drug used to treat lead poisoning in children, has limited efficacy in removing mercury from the body, according to research supported by the National Institutes of Health and published online in the Journal of Pediatrics.

Some families have turned to succimer chelation to lower mercury levels in the hopes that it will reduce symptoms of autism, noted the researchers, but this practice is not based on strong evidence of safety or efficacy.

To evaluate the effect of succimer in reducing blood mercury concentrations in children, researchers used blood samples obtained during the execution of the Treatment of Lead-exposed Children (TLC), a randomized, placebo-controlled study led by the National Institute of Environmental Health Sciences.

Total mercury concentration was measured in 767 blood samples taken before treatment, 768 samples drawn 1 week after treatment, and in a 20% random sample of children who received the maximum of 3 courses.

One week after treatment, the concentration of organic mercury decreased by 8% in the succimer-treated group and stayed the same in the placebo recipients, so that mean organic mercury concentrations in the succimer group were 93% of the levels in the control group.

After 3 courses of treatment, which took approximately 5 months to complete, mean organic concentrations in the succimer group were 82% of the levels in the control group.

The investigators explain that the reductions in organic mercury concentration in the succimer-treated children were modest-approximately 0.5 µg/L-and unlikely to be clinically meaningful. Succimer's main effect was to slow or prevent accumulation of organic mercury but not reverse it.

Because adherence to succimer was high in this study and the doses used were relatively high, larger doses or longer courses of treatment would most likely not alter the results, the investigators said.

Cao Y, Chen A, Jones RL, et al. Efficacy of succimer chelation of mercury at background exposures in toddlers: a randomized trial. J Pediatr. 2010. Epub ahead of print.