Lead poisoning treatment with EDTA

Murase, T., N. Horiba, I. Goto, O. Yamato, T. Ikeda, K. Sato. 1993. Erythrocyte ALA-d activity in experimentally lead-poisoned ducks and its change during treatment with disodium calcium EDTA. Res. Veterin. Sci. 55 252-257. 

Dimercaprol is FDA-approved as single-agent treatment of acute poisoning by arsenic and inorganic mercury and for the treatment of severe lead poisoning when used in conjunction with edetate calcium disodium (EDTA see below). Although studies of its metabolism in humans are limited, intramuscularly administered dimercaprol appears to be readily absorbed, metabolized, and excreted by the kidney within 4-8 hours. Animal models indicate that it may also undergo biliary excretion, but the role of this excretory route in humans and other details of its biotransformation are uncertain. 

This danger is minimal if calcium disodium EDTA is used as the chelating agent and it has now become the material of choice in cases of lead poisoning. Except in massive doses it is almost nontoxic and treatment with CaNa2EDTA results in a rapid depletion of lead in the soft tissues prolonged treatment is necessary for the removal of lead from bone72). 

C. Lead poisoning (except alkyl lead compounds). BAL has been used concomitantly with calcium EDTA (p 440) in the treatment of pediatric lead encephalopathy, where the joint regimen has been associated with accelerated decline in blood lead levels and increased urinary lead excretion. Note BAL is not for use as a single drug regimen in lead poisoning. 

B. Symptomatic poisoning by lead (without encephalopathy). Oral unithiol, 4-8 mg/kg orally every 6-8 hours, may be considered an alternative to suc-cimer (see p 501). Note Parenteral therapy with EDTA (see p 440) is preferable for treatment of severe lead intoxication (lead encephalopathy or lead colic), or for patients with extremely high blood lead concentrations (eg, blood lead >150 mcg/dL). 

There is no effective treatment of the poisoning. One case of toxic psychosis was treated with electroshock therapy (Boyd et at 1957). Symptomatic treatment with barbiturates has been recommended (Raz-SUDOV 1976). No effect is obtained by BAL, EDTA, or penicillamine which are used in the management of poisoning with inorganic lead (Boyd et at 1957, Cremer 1959, Kitzmiller et at 1954). 

EDTA salts are used for the treatment of heavy metal poisoning. Roosels and Vanderkeel142) were able to extract lead from urine in the presence of EDTA with dithizone by adding calcium to presumably release the lead from EDTA. In view of the fact that the formation constant of the lead-EDTA chelate is 20,000,000 times larger than that of the corresponding calcium chelate, it is doubtful that the calcium actually releases the EDTA from the lead. 

Because EDTA " binds strongly with many metal species, it is often added to commercial salad dressing to remove traces of metal ions from solntion (the presence of metal ions will accelerate the oxidation of oils in salad dressings). The other useful need for EDTA " is in the treatment of lead and mercury poisoning since EDTA " anions can form coordination complexes with the metal cations of Ctf, Pb and Hg (Figure 4.8). When bound to a metal atom, the six available lone pairs of electrons can wrap around the central metal ion, creating a stable coordinate covalent molecule, as shown here for Cu(EDTA). 

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