Fecal excretion applicators

In a study of pregnant rats that were exposed to radiolabeled methyl parathion by single dermal application, half-life elimination rate constants for various tissues ranged from 0.04 to 0.07 hour, highest values noted in plasma, kidneys, and fetus. Of the applied radioactivity, 14% was recovered in the urine in the first hour postapplication. By the end of the 96-hour study, 91% of the applied dose had been recovered in the urine. Fecal excretion accounted for only 3% of the administered dose (Abu-Qare et al. 2000). 

Skin tape stripping can be used to determine the concentration of chemical in the stratum comeum at the end of a short application period (30 min) and by linear extrapolation predict the percutaneous absorption of that chemical for longer application periods. The chemical is applied to skin of animals or humans, and after a 30-minute skin contact application time, the stratum comeum is blotted and then removed by successive tape applications. The tape strippings are assayed for chemical content. There is a linear relationship between this stratum comeum reservoir content and percutaneous absorption. The major advantages of this method are (1) the elimination of urinary and fecal excretion to determine absorption and (2) the applicability to nonradiolabeled determination of percutaneous absorption, because the skin strippings contain adequate chemical concentrations for nonlabeled assay methodology. 

No studies were located regarding the excretion of 3,3 -dichlorobenzidine in humans following dermal exposme. Fecal excretion in rats at 24 horns following 3,3 -dichlorobenzidine exposure was 19% of the administered dose, while urinaiy excretion accoimted for 8% (Shah and Guthrie 1983). Fifty-one percent of the administered dose was imabsorbed from the site of application at 24 hours. The remaining 49% was distributed throughout the body, feces and urine. 

Besides stopping the exposure to mercury and medically treating the symptoms, as in cases of acute or chronic mercury intoxication, the renal and fecal excretion of mercury may be increased by the application of a chelating agent. BAL (British Anti-Lewisite, Dimercaprol) is still used for this purpose in some countries, but has several disadvantages compared with more effective, water-soluble derivatives such as 2,3-dimer-... 

Most of the forementioned studies which examined the influence of various dietary fiber on the bioavailability of calcium by human subjects have depended upon the comparative measurements of calcium content of diets and calcium contents of stools and urine. As reviewed by Allen (3), calcium balance studies have distinct limitations relative to accuracy and precision. However, their ease of application and cost, laboratory equipment requirements, and real (or perceived) safety in comparison to available radioactive or stable isotope methods continue to make their use popular. In calcium balance studies, calcium absorption is assumed to be the difference between calcium excretion in the feces and calcium intake. Usually this is expressed as a percent of the calcium intake. This method assumes that all fecal calcium loss is unabsorbed dietary calcium which is, of course, untrue since appreciable amounts of calcium from the body are lost via the intestinal route through the biliary tract. Hence, calcium absorption by this method may underestimate absorption of dietary calcium but is useful for comparative purposes. It has been estimated that bile salts may contribute about 100 g calcium/day to the intestinal calcium contents. Bile salt calcium has been found to be more efficiently absorbed through the intestinal mucosa than is dietary calcium (20) but less so by other investigators (21). 

Dermal application of 14C-labeled 4-nitrophenol to dogs resulted in 11% of the dose (radioactive label) excreted in the urine over a period of 7 days. Fecal elimination was negligible. In rabbits, 78% of an absorbed dermal dose of C-labeled 4-nitrophenol appeared in the urine in 1 day. As in dogs, fecal elimination accounted for less than 1% of the absorbed dose (Snodgrass 1983). 

Chan et al. (1995), Riendeau et al. (1997) used a fecal 51 Cr excretion assay in rats and primates to detect gastrointestinal integrity after application of a selective cyclooxygenase inhibitor. 

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