Oral lead absorption

TABLE 8.4 Oral Lead Absorption Rate of Different Chemical Forms in Humans and Animals ... 

TABLE 8.5 Experimental Studies of Oral Lead Absorption from Different Environmental Media ... 

The highly polar ionic character of EDTA limits its oral absorption. Moreover, oral administration may increase lead absorption from the gut. Consequently, EDTA should be administered by intravenous infusion. In patients with normal renal function, EDTA is rapidly excreted by glomerular filtration, with 50% of an injected dose appearing in the urine within 1 hour. EDTA mobilizes lead from soft tissues, causing a marked increase in urinary lead excretion and a corresponding decline in blood lead concentration. In patients with renal insufficiency, excretion of the drug—and its metal-mobilizing effects—may be delayed. 

Acid is important in releasing vitamin B12 from food. A minor reduction in oral cyanocobalamin absorption occurs during proton pump inhibition, potentially leading to subnormal Bi2 levels with prolonged therapy. Acid also promotes absorption of food-bound minerals (iron, calcium, zinc) however, no mineral deficiencies have been reported with proton pump inhibitor therapy. 

However, R05 criteria were misused [50] although established for drugs, they were applied in everyday practice for post-HTS analysis in lead generation and identification. This resulted in compounds that were not easily amenable to further optimization. More restrictive criteria for leadlike compounds had to be formulated [51-54]. Besides oral drug absorption, BBB permeability has recently become of... 

High affinity for zinc and iron zinc and iron during treatment decrease efficacy replacement iron therapy may be necessary Not recommended for oral use should be delivered intravenously, typically over a course of 5-7 days requires hospitalization May cause increased lead absorption from G1 tract Side effects include nephrotoxicity... 

Absorption and tissue retention are dependent on level of lead exposure. Generally there is a nonlinear relationship between oral lead intake and blood lead (Lauwerys et al. 1977 Moore et al. 1977, 1982 Department of the Environment 1982) with the greatest increments in blood lead occurring at the lower range of environmental lead exposure. Tissue lead accumulation is closely associated with environmental lead exposure. 

Roels HA, Buchet J-P, Lauwerys R (1976) Impact of air pollution by lead on the heme biosynthetic pathway in school-age children. Arch Environ Health 31 310-316 Roels HAV Buchet J-P, Lauwerys RR, Bruaux P, Claeys-Thoreau F, Lafontaine A, Verduyn G (1980) Exposure to lead by the oral and the pulmonary routes of children living in the vicinity of a primary lead smelter. Environ Res 22 81-94 Rosen JF, Chesney RW.,i Hamstra A, DeLuca HF, Mahaffey KR (1980) Reductions in 1,25-dihydroxy vitamin D in children with increased lead absorption. N Engl J Med 302 1128-1131... 

Kostial et al. [37] demonstrated that 5-7 day old rats absorb at least 55% of single oral doses of Pb-203 while Forbes and Reina [20] reported that absorption was high prior to weaning but decreased rapidly thereafter. Garber and Wei [22] found that fasting enhanced lead absorption in mice. Low dietary levels of calcium, iron, zinc, copper, selenium, and vitamin D have been reported to enhance lead adsorption [64]. 

---