TABLE 1783 Adverse Effects of Chelating Agents

For symptomatic patients without encephalopathy, and for asymptomatic patients with elevated PbB levels requiring chelation, the use of BAL or DMSA (see discussion below) with or without CaNa2-EDTA and the dosing schedules are determined by the PbB levels, the presence or absence of symptoms, and changing practice as more experience with DMSA is obtained. Treatment may be initiated in the ED. Children who are symptomatic but not encephalopathic can be treated as discussed earlier, except with doses of BAL, 50 mg/m2, and CaNa2-EDTA, 1000 mg/m2 per 24 h, or with DMSA plus EDTA. A retrospective study of 45 children with lead levels of 45 pg/dL or more treated either with BAL plus EDTA or DMSA plus EDTA found comparable reductions in lead levels, with fewer side effects in the DMSA group.10 The Centers for Disease Control and Prevention (CDC) recommend immediate chelation therapy for children with blood lead levels of 70 pg/dL or more.8 Symptomatic, nonencephalopathic adults may be treated with BAL and CaNa2-EDTA, with CaNa2-EDTA alone, or with DMSA.

In asymptomatic patients, the standards for determining lead toxicity and the need for treatment differ for children and adults. In asymptomatic children, chelation therapy should be performed if the PbB level is 45 pg/dL or more. As indicated earlier, chelation therapy should begin immediately (i.e., in the ED) if the PbB lead level is 70 pg/dL or more. If the PbB level is 20 to 44 pg/dL, treatment strategies include environmental and nutritional evaluation, medical examination, and possibly chelation therapy, either with DMSA, CaNa2-EDTA, or D-penicillamine. For children with PbB levels between 10 and 19 pg/dL, interventions include nutritional and medical evaluation, repeat screening PbB levels, and environmental investigation for persistently high levels. In asymptomatic adults, the guidelines are less rigorous. In asymptomatic workers, a PbB level of less than 40 pg/dL is accepted as normal, levels of 40 to 50 pg/dL require increased job surveillance, and levels greater than 50 pg/dL require temporary removal from the job until the PbB level drops below 40 pg/dL. Details on therapy for these various groups can be found in standard toxicology references.

In patients in whom the lead level is elevated on a capillary stick sample, it is best to await verification on blood, unless the clinical presentation strongly supports lead toxicity. Capillary samples may give false-positive results, as noted earlier.

Two oral chelating agents are being used in lead toxicity. DMSA, an analogue of dimercaprol, effectively chelates lead in adults and children. 1112 Its advantages include oral administration without increasing lead absorption from the gastrointestinal tract, no serious adverse effects, and minimal chelation of essential metals. High cost is its main disadvantage. The dose is 10 mg/kg every 8 h for 5 days, followed by the same dose every 12 h for 14 days. Repeat treatment may be necessary after a 2-week drug-free period. D-Penicillamine is a less effective chelating agent but has the advantage of being inexpensive. It has been used for outpatient therapy in both asymptomatic children and adults with mild PbB elevations.

DISPOSITION Removal of the source of lead is mandatory for all patients. Patients should not be discharged to their former environments until appropriate deleading and decontamination measures have been accomplished. Family members and coworkers should be evaluated for occult lead toxicity.

A guide for hospitalization includes

1. All children with symptoms or with a PbB level of 70 pg/dL or more

2. All adults with CNS symptoms

3. All patients with suspected toxicity when returning to the environment is considered dangerous

PROGNOSIS Approximately 85 percent of patients who suffer encephalopathy develop permanent CNS damage, including seizures, mental retardation in children, and cognitive deficits in adults. Abdominal colic usually subsides within days after beginning chelation therapy, and other acute manifestations clear within 1 to 16 weeks with therapy. Lead-induced nephropathy may be partially reversible with chelation therapy.

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