Absorption of ingested

Sorbitan sesquioleate emulsions of petrolatum and wax are used as ointment vehicles in skin treatment. In topical appHcations, the inclusion of both sorbitan fatty esters and their poly(oxyethylene) derivatives modifies the rate of release and promotes the absorption of antibiotics, antiseptics, local anesthetics, vasoconstrictors, and other medications from suppositories, ointments, and lotions. Poly(oxyethylene(20)) sorbitan monooleate, also known as Polysorbate 80 (USP 23), has been used to promote absorption of ingested fats from the intestine (245). 

The site and mechanism of absorption of ingested americium are not known. Based on studies of plutonium, it is likely that americium absorption occurs, at least to some extent, in the small intestine. Studies of the absorption of plutonium in preparations of in situ isolated segments of small intestine of immature miniature swine indicate that absorption of actinides can occur along the entire small intestine, with the highest rates of absorption occurring in the duodenum (Sullivan and Gorham 1982). 

Absorption of americium is greater in iron deficient animals than in iron replete adult animals (Sullivan and Ruemmler 1988 Sullivan et al. 1986) (see Section 3.4.1.2). Concurrent oral exposure to Fe3+ and americium also appears to increase the absorption of ingested americium the latter effect may result from redox reactions in the gastrointestinal tract catalyzed by Fe3+ (Sullivan et al. 1986). These differences are accounted for in the discussions and dosimetric/metabolic models of the ICRP (1989, 1993) and the NEA (1988). 

Children s Susceptibility. No studies were located in which comparisons were made between the sensitivity of children and adults to the toxicity of americium. Animal studies indicate that juvenile dogs are less susceptible than adults to americium-induced bone cancer (Lloyd et al. 1999). No direct evidence was located to indicate that the pharmacokinetics of americium in children may be different from that in adults. Based on dosimetric considerations related to differences in the parameters of available models, as well as studies in animals, it seems likely that children may be more susceptible to americium toxicity than are adults by virtue of age-related differences in pharmacokinetics. Absorption of ingested americium may be as much as 200 times greater in neonatal animals than in adults. (Bomford and Harrison 1986 David and Harrison 1984 Sullivan et al. 1985). 

Bomford JA, Harrison JD. 1986. The absorption of ingested Pu and Am in newborn guinea pigs. Health Phys 51(6) 804-808. 

David AJ, Harrison JD. 1984. The absorption of ingested neptunium, plutonium and americium in newborn hamsters. Int J Radiat Biol 46(3) 279-286. 

Mineral oil may accumulate to some degree in liver and fatty tissues after absorption of ingested mineral oil hydraulic fluids, as indicated by experiments with rats given single, 0.66-mL, oral doses of tritiated mineral oil (Ebert et al. 1966). Twenty-four hours after administration, the concentrations of tritiated mineral oil in liver and fat were approximately seven-fold greater than those in kidney and brain other tissues were not examined. 

Heard and Chamberlain 1982 James et al. 1985 Rabinowitz et al. 1976, 1980). The general consensus is that food in the gastrointestinal tract decreases absorption of ingested lead, although the exact mechanisms by which this occurs are not entirely understood. 

The toxicokinetics of lead in children appears to be similar to that in adults, with the exception of the higher absorption of ingested lead in children. Most of the lead body burden in both children and adults is in bone a slightly large fraction of the body burden in adults resides in bone (Barry 1975). The difference may reflect the larger amount of trabecular bone and bone turnover during growth trabecular bone has a shorter retention halftime for lead than does cortical bone (See Section 2.3.3 for details). 

Rat Supplemented diet with (in g/kg) FA Absorption ( % of ingested dose) Foregut (small intestine/ stomach) Cecum Colon Residues FA in plasma (pM) ... 

Methods for Reducing Toxic Effects. There are no established methods for reducing absorption of DEHP or metabolites because the mechanism of absorption is not known. There have been no studies of compound-specific techniques for reducing DEHP body burden. External contact with DEHP can be treated by thoroughly washing the affected area. Activated carbon, possibly combined with a cathartic, will diminish absorption of ingested DEHP from the gastrointestinal tract (HSDB 2000). 

Leggett, R.W., Harrison, J.D. (1995). Fractional absorption of ingested uranium in humans. Health Phys. 68 484-98. 

No studies were located that quantitated the absorption of ingested 1,1-dichloroethane in humans or animals. However, when 700 mg [ C]-1,1-dichloroethane/kg was orally administered to rats and mice, absorption was evidenced by the presence of radiolabel in expired air and the presence of radiolabeled metabolites in urine, though there was no quantitative assessment made of the extent or rate of absorption (Mitoma et al. 1985). 

The value for the fractional absorption of ingested uranium (fj) was adjusted from the adult value of 0.02 (2%) to a value of 0.04 (4%) for children under the age of 1 year. This adjustment was made based on animal data (Sullivan et al. 1980b Sullivan and Gorham 1982) and information on postnatal changes in the human gastrointestinal tract. For ages over 1 year, the adult value for fractional absorption was used. 

No information is available on whether children differ from adults in their weight-adjusted intake of uranium. The fractional absorption of uranium (as uranyl nitrate and uranyl citrate) by the oral route was higher in neonatal than in adult rats and swine (Sullivan 1980b Sullivan and Gorham 1982). In a mathematical model developed by the International Commission for Radiological Protection (ICRP) for risk assessment, one of the assumptions is that the fractional absorption of ingested uranium is twice as high in children under the age of 1 year compared to adults. 

Among factors that may modify gastrointestinal absorption of ingested chemicals, the presence of food in the tract is one of the most important. The presence of food in the stomach will delay the absorption of weak organic acids at that site. The presence of lipid-rich food will delay the emptying of the gastric content into the intestine and thus also delay the absorption of chemicals. Conversely, an empty stomach facilitates absorption, a situation that is almost always beneficial in drug therapy. 

PTH also increases intestinal calcium absorption by increasing 1,25 (OH) 2D. PTH is a major trophic factor for renal 25(OH)t>-la-hydroxylase. It increases the conversion of 25(0H)D to the active vitamin D metabolite, l,25(OH)2D. Calcium is absorbed principally in the duodenum, although it can also be absorbed by the distal small bowel and colon. About 30% of a daily calcium intake of 1 g (25 mmo ) is absorbed. Approximately 100 mg (2.5 mmol) of calcium is secreted into gut lumen by intestinal secretion therefore net calcium absorption is 200 mg (5.0 mmol)/day. Calcium is absorbed by passive diffusion and by an active transport system. It is estimated that passive diffusion accounts for absorption of about 10% of ingested calcium per day. Active calcium absorption in the duodenum is under the control of l,25(OH)2D. This vitamin D metabolite increases the intestinal cell synthesis of a calcium-binding protein (CaBP), which enhances the net absorption of ingested calcium. 

Aromatic EC>9-EC16 Fraction. No data regarding the extent or rate of absorption of ingested naphthalene or monomethyl naphthalenes were available, except for a report that 80% of an oral dose of 2-methyl naphthalene was recovered as metabolites in the urine of rats within 24 hours (ATSDR 1995e). Studies with animals indicate that orally administered isopropylbenzene (cumene) rapidly appeared in the blood and that 90% of the administered dose was accounted for in urinary metabolites (EPA 1987a, 1997b). 

Data regarding the rate or extent of absorption of ingested 1,1,1-trichloroethane in humans are not available, but based on extensive animal data, it is anticipated that oral absorption of 1,1,1-trichloroethane will be extensive in humans. Animal experiments indicate that 1,1,1-trichloroethane is rapidly and completely absorbed by the gastrointestinal tract. Maximum levels of 1,1,1 -... 

Summary of Estimates of Absorption of Ingested Strontium in Humans 3-8. Reference Respiratory Values for a General Caucasian Population at Different Levels of Activity... 

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