Excretion fecal

Renal excretion is faster and elimination of excreted radioactivity from the body by frequent voiding can reduce the overall body burden more quickly than can fecal excretion via the biUary tree and gut. 

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). 

The only relevant information located was that administration of cholestyramine resin may increase fecal excretion of endosulfan trapped in the enterohepatic circulation (Dreisbach and Robertson 1987 Howland 1990 HSDB 1999). 

Excretion is the process by which a substance leaves the body. The most common ways are via the kidneys and via the gut. Renal excretion is favored by water-soluble compounds that can be filtered (passively by the glomeruli) or secreted (actively by the tubuli) and that are collected into urine. Fecal excretion is followed by more lipid substances that are excreted from the liver into the bile, which is collected in the gut and passed out by the feces. Other routes of excretion are available through the skin and the lungs. 

Palmer 1989 Robinson et al.1983). However, the ratio was almost certainly affected by initial chelation with Ca-DPTA, followed by daily intravenous therapy with the chelating agent, Zn-DPTA, treatments that would have increased the urinary excretion of americium (Breitenstein and Palmer 1989). The above not withstanding, the observations made on this subject demonstrate that fecal excretion was an important pathway of excretion in this subject long after mechanical clearance of americium from the respiratory tract would have been complete. This is consistent with observations made in nonhuman primates that show that americium is excreted into bile (see Section 3.4.4.4). However, the extent to which the biliary excretion pathway in humans might resemble that of nonhuman primates is not known. 

The large contribution of the fecal route to excretion of absorbed americium appears to be the result of excretion of americium into the bile. In monkeys that received an intravenous injection of americium citrate,241 Am was detected in gall bladder bile and its concentration increased as the relative rate of fecal excretion increased over time post injection (Durbin 1973). Durbin (1973) estimated that at bile production rates similar to humans, biliary excretion could have accounted for most, if not all, of the fecal excretion of americium observed in the monkeys. 

Predictions based on the model have been compared to observed urinary or fecal excretion of americium in humans. Model predictions agreed reasonably well with the empirical observations (Leggett 1992). 

Fecal excretion may gain relative importance as an excretory route for tri-/xrra-cresyl phosphate as doses approach levels of 100 mg/kg (Kurebayashi et al. 1985 NTP 1988). Fecal excretion of tn-m-cresyl phosphate appears to be predominant in rats even at a dose level of 200 mg/kg (NTP 1988). 

In contrast, urinary excretion of radioactivity from tri-para-cresyl was the predominant excretory route at low doses (0.5 or 2 mg/kg), while fecal excretion was the primary route at higher doses (20 or 200 mg/kg). 

Lead undergoes biliary excretion in the dog, rat, and rabbit biliary excretion is presumed to contribute to fecal excretion of lead in humans (EPA 1994b Klaassen and Shoeman 1974 O Flaherty 1993). The mechanism of biliary excretion has not been elucidated. 

Species Category Fecal excretion contribution (%) Urine excretion (fig day-1) Excreted hormones... 

Ohzawa et al. [Ill] studied the metabolism of miconazole after a single oral or intravenous administration of 14C miconazole at a dose of 10 mg/kg. After 1 h oral or intravenous administration to male rats, the four known metabolites besides the unchanged form were observed in the plasma, and the five unknown metabolites were observed in the plasma. At 24 h, metabolites were not detected in plasma except one of the known metabolites. After oral administration to female rats, the unchanged form and four of the known metabolite along with one of the unknown metabolites were observed in the plasma, but one of the known metabolites and three of the unknown metabolites were not detected. After oral or intravenous administration to male rats, two of the known metabolites and five of the unknown metabolites were observed in the urine collected until 24 h. After oral or intravenous administration to male rats, four of the known metabolites and five of the unknown metabolites and one of the known metabolites besides the unchanged form were observed in the feces collected until 24 h. The fecal excretion of the major known metabolite, within 24 h after oral or intravenous administration was 19.4% or 13.3% of the administered radioactivity, respectively. One of the unknown metabolite was isolated from plasma after oral administration to female rats. 

Ohzawa et al. [113] studied the absorption, excretion, and metabolism of miconazole after a single oral administration of 14C miconazole at a dose of 10 mg/kg to male dogs. After administration of 14C miconazole, the blood concentration of radioactivity reached the maximum level at 4 h, and then declined slowly with a half-life of about 26 h. The plasma concentration reached the maximum level at 5 h and then declined slowly with a half-life of 30 h. After the administration of miconazole, the plasma concentration of the unchanged form reached the maximum level at 3 h and then rapidly declined with half-life of about 4.3 h. Within 168 h after administration of 14C miconazole, urinary and fecal excretion amounted to about 6% and 66% of the administration radioactivity, respectively. After administration of 14C miconazole, the plasma concentration of the unchanged form rapidly declined, but the plasma level of two major metabolites reached maximum at 5 and 12 h, respectively and then declined. 

In studies with normal adult animals, orally administered radiocerium moves rapidly through the gastrointestinal tract. About 0.96 of a cerium nitrate solution administered orally to rats was excreted within 24 hours (Sagan and Lengemann, 1973). However, external irradiation of the gastrointestinal tract with a 137Cs source (800 R) delayed excretion of the radiocerium. Only about 0.85 of the administered cerium was excreted by 3 days but 0.992 was excreted by 4 days. In swine, 0.98 of an oral dose of radiocerium was excreted by 3 days (Miller et al., 1969) while in cattle, radiocerium placed in the rumen required 3.7 days for 0.9 of the dose to be excreted. Fecal excretion of the cerium still occurred after 4 days. When radiocerium was placed in the abomasum of cattle, it was almost entirely voided in 1.2 days. 

Lma = L d + (G.I. contents - Fe4d, where L d and (G.I. contents are the amounts of nuclide in liver and G.I. contents 4 days after injection, and Fe4d is the cumulative fecal excretion at 4 days. b Calculated from data for humeruB and femur. 

The predominant route of excretion in rats is via urine (Gut et al. 1985 Tardif et al. 1987 Young et al. 1977). In rats exposed to 5 ppm of 1- C-acrylonitrile for 6 hours, 68% of the absorbed radioactivity was excreted in the urine within 220 hours, with 3.9% in the feces, 6.1% in expired air as CO2, and 18% of the radioactivity being retained in the body tissues. Following exposure to a higher concentration (100 ppm), a larger fraction of the dose was recovered in urine (82%) and a smaller fraction (2.6%) was retained in the body (Young et al. 1977), indicating that urinary excretion is dose-dependent. Percent fecal excretion was similar at both doses. 

Intestinal inflammation was assessed by fecal excretion of " In-labeled neutrophils while blood loss was quantitated via fecal excretion of 51Cr4abeled red cells. The urinary excretion ratio or51 Cr-EDTA//.-rhamnose was used as an index of intestinal permeability. ... 

During the first day after each dose, 20% was excreted into urine, 0.5% into feces, and 20% into bile. The addition of 4% cholestyramine to diets for 6 days resulted in increased fecal excretion by a factor of 18 and increased total body burden excretion by 1.4 times (Rozman etal. 1982)... 

When 20 mg/kg of methimazole was administered i.p. or orally to rats, urinary methimazole glucuronides accounted for 36-48% of the dose in 24 hours. The only other urinary metabolite accounted for 10-20% and was not characterized. An additional 14-20% of methimazole was excreted unchanged in 24 hour urine. The bile contained methimazole glucuronide and two unidentified metabolites. One of which was the same as the unidentified urinary metabolites. Plasma proteins bound 5% of methimazole which had no affinity for any specific tissue. Methimazole had a much greater CHCI3/H2O partition coefficient and 1 0 solubility than did propylthiouracil. Between 77 and 95% of the methimazole was excreted in the urine and approximately 10% in the bile. Since fecal excretion was neglegible an enter-ohepatic circulation was present. The half life of urinary excretion was 5-7 hours regardless of the route of administration (15). 

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