Urinary Excretion of Essential Metals Following Intravenous Calcium Disodium Edetate: an Estimate of Free Zinc and Zinc Status in Man

Ethylenediaminetetraacetic acid (EDTA) is a powerful metal chelating agent used in the treatment of lead poisoning. EDTA also binds strongly to other metals. Thus, following intravenous infusion of CaNa2EDTA in healthy subjects the urinary excretion of calcium, copper, iron, magnesium and zinc were assessed. CaNa2EDTA significantly increased the urinary excretion of all metals except magnesium with greatest increases for iron (x 3.8 above baseline) and zinc (x 22). In addition, an in vitro dialysis study with a simplified serum showed that zinc (4.1 X 10(-3) mumol/h) was taken up more rapidly than iron (2.9 X 10(-3) mumol/h) by EDTA. The degree of binding of iron and zinc by EDTA depends on two factors: namely, the affinity of EDTA for Zn2+ and Fe3+, and the levels of unbound hydrated Zn2+ and Fe3+ ('free' ions). Despite differences in the rate of chelation of Zn2+ and Fe3+ by EDTA we show that the measurements of (a) circulating free iron, from routine clinical measurements of transferrin bound iron, and (b) the ratio of zinc:iron excreted in urine could provide an estimate of circulating free zinc, and thereby of zinc status, in man. In addition, EDTA treatment should be evaluated for patients with iron overload.