Edetate calcium disodium excretion

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. 

Because the onset of lead poisoning usually is insidious, it often is desirable to estimate the body burden of lead in individuals who are exposed to an environment that is contaminated with the metal. In the past, the edetate calcium disodium (CaNaJlDTA) provocation test was used to determine whether there is an increased body burden of lead in those for whom exposure occurred much earlier. The provocation test is performed by intravenous administration of a single dose of CaNa DTA (50 mg/kg) followed by collection of urine for 8 hours. The test is positive for children when the lead excretion ratio (pg of lead excreted in the urine per mg of CaNa DTA administered) is >0.6 it also may be useful for therapeutic chelation in children with blood levels of 25 5 pg/dL. This test is not used in symptomatic patients or in those whose concentration of lead in blood is >45 pg/dL because these patients require the proper therapeutic regimen with chelating agents (see below). 

Edetic acid is a metal chelator. The effect of an intravenous dose of 1 g of calcium disodium edetate on the urinary excretion on the elements aluminium, boron, barium, calcium, copper, iron, lead, magnesium, manganese, phosphorus, potassium, sihcon, sodium, strontium, sulphur, and zinc was measured in healthy volunteers. The ratio of the increase of urinary elimination was about two for iron, five for aluminium, lead, and manganese, and 15 for zinc (1). 

Trisodium edetate (therapeutically equivalent to disodium edetate) i.v. chelates calcium and the inert complex is excreted by glomerular filtration. Although it is rapidly effective, it causes pain in the limb receiving the infusion and may cause renal damage. 

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