Chelation therapy in children as treatment of sequelae in severe lead toxicity

Comparison of dimercaptosuccinic acid and calcium disodium ethylenediaminetetraacetic acid versus dimercaptopropanol and ethylenediaminetetraacetic acid in children with lead poisoning

OBJECTIVES

To compare the response to dimercaptopropanol (BAL) and calcium disodium ethylenediaminetetraacetic acid (EDTA) versus orally administered meso-2,3-dimercaptosuccinic acid (DMSA) and EDTA in children with lead poisoning.

METHODS

Retrospective review of medical records of children admitted to MetroHealth Medical Center with a whole blood lead (BPb) concentration of 2.17 mumol/L (45 micrograms/dl) or more (or less than 2.17 mumol/L and not a candidate for outpatient oral chelation) and treated with BAL + EDTA or DMSA + EDTA. In each group, the mean BPb values at the end of therapy and at 14 and 33 days after chelation were compared with pretreatment BPb by the Wilcoxon signed-rank test, whereas the Mann-Whitney U test was used to compare percentage change from pretreatment at each follow-up day between the two groups.

RESULTS

Twenty-three children received BAL + EDTA and 22 received DMSA + EDTA. The BPb values (mean +/- SD) at the end of therapy and at 14 and 33 days after chelation were significantly lower than pretreatment in both groups (BAL + EDTA: 17 +/- 10, 34 +/- 7, 36 +/- 11 vs 58 +/- 14 micrograms/dl, p < 0.02, 0.01, 0.001, respectively; DMSA + EDTA: 10 +/- 4, 30 +/- 10, 30 +/- 14 vs 50 +/- 10 micrograms/dl, p < 0.01, 0.001, 0.01, respectively). The percentage reduction (mean +/- SD) in BPb from pretreatment at the end of therapy and on days 14 and 33 after chelation did not differ between the groups (BAL + EDTA: -71.2% +/- 19.8%, -40.2% +/- 13.8%, -37.1% +/- 17%; DMSA + EDTA: -79.9% +/- 8.7%, -38.3% +/- 21.6%, -37% +/- 32%; p > 0.20). Elevation of alanine aminotransferase and vomiting during therapy were observed more frequently in the BAL + EDTA group compared with the DMSA + EDTA group.

CONCLUSIONS

Treatment with DMSA or BAL combined with EDTA results in a comparable reduction in BPb.

Preventing lead poisoning in children

Lead poisoning is the most significant and prevalent disease of environmental origin among US children. Despite over 100 years' knowledge of the special hazards of lead exposure for young children, it has taken over a century for effective primary prevention to be adopted. Obstacles to primary prevention have included deliberate campaigns by industry to prevent restrictions upon such uses on lead as plumbing, paints, and gasoline additives; influence of industrial support of biomedical research at major US medical schools: lack of appropriate policy mechanisms to identify and control lead exposures; and opposition to investing resources in lead poisoning prevention. The removal of lead from gasoline, which began in the United States in 1972 and was completed in 1995, has resulted in almost fourfold reductions in median blood lead levels in US children from 1976 to 1991. Increased screening and interventions to identify and abate lead sources, such as lead in housing, also contributed to this major public health success. Nevertheless, lead exposures remain prevalent, although increasingly less generally distributed. Perhaps because of the renewed "ghettoization" of lead, support for lead poisoning prevention has waned. Objections to investing public and private resources in screening and source abatement have challenged the continuing commitment of public health officials to prevention. The demonstrable success and social benefits of preventing lead toxicity are cited in support of continued preventive health policies.

Review of the multiple chemical exposure factors which may disturb human behavioral development

Previous research both in humans and laboratory animals provides evidence that prenatal exposure to metals, pollutants and drugs may impair the neurobehavioral development of the offspring. This may induce mental and psychomotor disturbances as well as learning, behavioral and sensory disorders. However, proof for a strict causality between some low-level exposures to chemicals and behavioral developmental dysfunctions, is often considered still not to be established. The pertinent studies on neurobehavioral developmental toxicity of individual substances (lead, cadmium, organic solvents, PCBs, alcohol, nicotine, diazepam) are reviewed, and the methodologies and conclusions, the missing aspects and the existing problems which still need to be solved in further studies, are discussed. In addition, the necessity of undertaking a broad prospective cohort study on multifactorial influences on the behavioral development of children is emphasized.

Efficacy of oral meso-2,3-dimercaptosuccinic acid therapy for low-level childhood plumbism

OBJECTIVE

To compare the response to oral meso-2,3-dimercaptosuccinic acid (DMSA) treatment in children with an initial blood lead (BPb) concentration less than versus more than 2.17 mumol/L (45 micrograms/dl).

DESIGN

Retrospective cohort study.

SETTING

Regional referral lead treatment program in an urban children's hospital.

PATIENTS

Thirty consecutive children, median age 34 months (range, 5 to 161 months), with an initial BPb concentration 0.97 to 2.90 mumol/L (20 to 60 micrograms/dl) selected for DMSA use. Reasons for DMSA use included BPb concentration > 2.17 mumol/L (11 children), complications with penicillamine therapy (11), chronic renal failure (1), and compassionate use (7). All patients received required environmental hazard reductions before drug administration.

RESULTS

Group 1 (n = 23) had a mean BPb concentration of 1.50 mumol/L (31 micrograms/dl), and group 2 (n = 7) had a mean BPb concentration of 2.41 (51 micrograms/dl). Sixteen patients (70%) in group 1 and five patients (71%) in group 2 had had previous chelation therapy (p value not significant). No significant difference was found in the mean percentage of the reduction of BPb concentration during treatment of group 1 (60%) versus group 2 (58%). The mean BPb concentration in group 1 rebounded to 70% of pretreatment values by mean day 41; the BPb concentration in group 2 rebounded to 69% by day 37 (p value not significant). Prior chelation therapy did not result in a significant difference in either the percentage reduction of BPb concentration or the percentage of rebound BPb.

CONCLUSION

DMSA is equally effective in acutely lowering BPb concentration in children with BPb concentrations less than and greater than 2.17 mumol/L.

The comparative developmental neurotoxicity of lead in humans and animals

The effects of lead on neurobehavioral development have been extensively investigated in humans as well as animals. This valuable lode of research findings offers a basis for comparing the developmental neurobehavioral toxicity of lead across species and for assessing the validity of animal models of developmental neurotoxicity. Comparisons of human and animal findings suggest that the greatest qualitative similarities involve relatively complex behavioral processes such as cognition and learning. Quantitative comparisons based on dose-response relationships for these endpoints are difficult to make because the relationships are sometimes nonmonotonic (U-shaped) and because blood lead levels may not be directly comparable between species. However, the lowest levels of exposure at which developmental neurobehavioral effects have been observed are similar: 10-15 micrograms/dl in children, less than 15 micrograms/dl in primates, and less than 20 micrograms/dl in rodents. Although the convergence between animal and human findings for other neurobehavioral endpoints is not as striking, sensory-evoked potentials and communicative processes offer two promising areas for continued investigation and cross-species comparison.

Communication disturbances and hyperactive/conduct-disturbed behavior

This study examines mother-child communication as one factor in the development of conduct-disturbed/hyperactive boys. Three groups of school-age children were compared: a group including conduct-disturbed/hyperactive boys who had a significant insult in their perinatal/developmental history; a group of conduct-disturbed/hyperactive boys in whom no insult could be found; and a group of normally active/non-conduct-disturbed/hyperactive boys. It was hypothesized that disturbed communication between mother and son would be found in boys who were conduct-disturbed/hyperactive, whether or not there was a probable organic cause for their dysfunction, and this hypothesis was confirmed. In addition, it was found that the communication patterns in children who had a probable organic etiology for their disturbance were different from those found in the group lacking an organic etiology. However, both of these groups exhibited communication patterns that were more disturbed than the communication from mother to son in the normally active, non-conduct-disturbed group.

Low level lead exposure during lactation increases rough and tumble play fighting of juvenile rats

Lactating rats were given distilled water or distilled water containing 0.067% lead chloride (500 ppm lead) as their sole source of drinking fluid from Days 1-21 of lactation. Activity, social investigation and rough and tumble play fighting behaviors of the offspring were observed on Day 26 and activity and play solicitation behaviors on Day 36. Although lead treatment reduced the mothers' fluid intake, there were no effects on pup growth and activity or on maternal behaviors. When paired with a group-housed stimulus animal on Day 26, lead-treated subjects had increases in the two measures of play fighting (crossover and pinning), and in social investigation, relative to controls. When tested with a scopolamine-treated, non-playful stimulus on Day 36, increased crossover frequencies were observed in lead-treated subjects when compared with controls. Two-min activity levels on Days 26 and 35 were unaffected by lead exposure. These results indicate that social interactive behaviors of juvenile rats are effective tools in the assessment of exposure to toxic substances early in development.

Lead intoxication

Lead intoxication was recognised as early as 2000 BC and the widespread use of lead has been a cause of endemic chronic plumbism in several societies throughout history. In the twentieth century, lead intoxication is still a common problem. In children it is largely due to ingestion of pica and environmental exposure, whereas adult groups at greatest risk are the industrially exposed: thus, screening of these workers should be undertaken at regular intervals. The clinical features of lead intoxication are nonspecific and often go unrecognised. The early manifestations are largely neuropsychiatric, followed by more significant disturbances of the central and peripheral nervous systems, symptomatic gastrointestinal, musculoskeletal, haematological and endocrine abnormalities. The association of lead poisoning with renal disease is well documented and must be considered, particularly if there is associated hypertension and/or gout. Blood lead concentrations are an unreliable predictor of body lead stores as they are indicative only of recent exposure. Haematological parameters have been used to assess those at risk of toxicity, but although more reliable than blood concentrations, they also fail to predict those patients at risk of toxicity. The recommended assessment for patients with suspected lead intoxication is a calcium disodium edetate chelation test, which is a sensitive marker for assessing body stores and subsequent intoxication. In children the dosage should be 50 mg/kg up to 1000 mg, and in adults 1000 mg administered intravenously or 2000 mg intramuscularly in divided doses 12 hours apart with subsequent 72 hour urinary lead estimations. Lead excretion levels greater than 350 micrograms/72 hours should be considered as suggestive of intoxication, particularly if supported by historical, clinical or biochemical evidence of lead exposure. Treatment of patients with positive chelation tests involves symptomatic treatment and a course of chelation therapy utilising calcium disodium edetate in doses similar to those used for testing, and in the more severely intoxicated patient, the addition of dimercaprol in doses of 75 mg/m2 every 4 hours to a total of 300 mg/m2/day. The safety of these treatment regimens is well documented.