Gastrointestinal elimination

For orally administered peptides and proteins, the gastrointestinal tract is the major site of metabolism. Presystemic metabolism is the primary reason for their lack of oral bioavailability. Parenterally administered peptides and proteins, however, may also be metabolized in the intestinal mucosa following intestinal secretion. At least 20% of the degradation of endogenous albumin takes place in the gastrointestinal tract [13]. 

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Cathartics, such as magnesium citrate and sorbitol, were thought to decrease the rate of absorption by increasing gastrointestinal elimination of the poison and the poison-activated charcoal complex, but their value is unproven. Poisoned patients do not routinely require the administration of a cathartic, and it is rarely, if ever, given without concurrent activated charcoal administration. If used, a cathartic should be administered only once and only if bowel sounds are present. Infants, the elderly, and patients with renal failure should be given saline cathartics cautiously, if at all. ... 

Mesitylene. One of the principal derivatives of mesitylene is the stericaHy hindered phenol of the stmcture shown in Eigure 4. Its trade name is Ethanox 330 and it is produced by Albemarle Corporation (formerly Ethyl Corporation) (31). Ethanox 330 is an important noncoloring antioxidant and thermal stabiHzer for plastics, adhesives, mbber, and waxes (qv) (32,33) (see Antioxidants). The oral toxicity of Antioxidant 330 is extremely low (oral LD q in rats >15 g/kg) since its large size, C H gO, effectively eliminates absorption from the gastrointestinal tract. 

Sucralfate [54182-58-0] an aluminum salt of sucrose octasulfate, is used as an antacid and antiulcer medication (59). Bis- and tris-platinum complexes of sucrose show promise as antitumor agents (60). Sucrose monoesters are used in some pharmaceutical preparations (21). A sucrose polyester is under evaluation as a contrast agent for magnetic resonance imaging (mri) (61). Oral adrninistration of this substance opacifies the gastrointestinal tract and eliminates the need for purging prior to mri. 

Ibuprofen is the most thoroughly researched 2-ary lpropionic acid. It is a relatively weak, non-selective inhibitor of COX. In epidemiological studies, ibuprofen compared to all other conventional NSAIDs, has the lowest relative risk of causing severe gastrointestinal side effects. Because of this, ibuprofen is the most frequently used OTC ( over the counter , sale available without prescription) analgesic. Ibuprofen is highly bound to plasma proteins and has a relatively short elimination half-life ( 2 h). It is mainly glucuronidated to inactive metabolites that are eliminated via the kidney. 

These studies represent the first report of the metabolism of brevetoxins by mammalian systems. PbTx-3 was rapidly cleared from the bloodstream and distributed to the liver, muscle, and gastrointestinal tract. Studies with isolated perfused livers and isolated hepatocytes conflrmed the liver as a site of metabolism and biliary excretion as an important route of toxin elimination. [ H]PbTx-3 was metabolized to several compounds exhibiting increased polarity, one of which appeared to be an epoxide derivative. Whether this compound corresponds to PbTx-6 (the 27,28 epoxide of PbTx-2), to the corresponding epoxide of PbTx-3, or to another structure is unknown. The structures of these metabolites are currently under investigation. 

Milieu conditions in gastrointestinal tract can influence the pectin structure and properties. Under the acid conditions of the stomach (pH 2-4) extraction of pectin from plant cell walls and hydrolysis of side chains can occur. In small intestine (pH 5-6) -elimination of main chains or de-esterification seems to be possible. In caecum and colon (pH 6-8) a strong fermentation of pectin takes place causing depolymerization to oligomers and leading to formation of short chain fatty acids and gases. The presence of OligoGalA is not yet clarified. 

Diquat and paraquat are quaternary ammonium compounds largely used as contact herbicides and crop desiccants. When systemic absorption occurs, paraquat and diquat are rapidly distributed into the body. Paraquat primarily accumulates in the lungs and kidneys, while the highest diquat concentrations have been found in the gastrointestinal tract, liver, and kidneys (WHO, 1984). Urine is the principal route of excretion for both diquat and paraquat, which are primarily eliminated as unmodified compounds. Occupationally exposed workers can be monitored by measuring paraquat and diquat concentrations in urine samples (Table 6). Blood concentrations are useful to monitor acute poisoning cases. 

Only a subset of the parameter values in the O Flaherfy model require inputs from the user to simulate blood and tissue lead concentrations. Lead-related parameters for which values can be entered into the model include fractional absorption from the gastrointestinal tract partition coefficients for lead in nonbone tissues and in the surface region of bone maximum capacity and half-saturation concentration for capacity-limited binding in the erythrocyte elimination clearance fractional clearance of lead from plasma into forming bone and the restricted permeability coefficients for lead diffusion within bone, from plasma into bone, and from bone into plasma (O Flaherty 1991a). 

All of the organ systems in the body, except the reproductive system, contribute to the maintenance of homeostasis (see Table 1.1). For example, the gastrointestinal tract digests foods to provide nutrients to the body. The respiratory system obtains oxygen and eliminates carbon dioxide. The circulatory system transports all of these materials and others from one part of the body to another. The renal system eliminates wastes and plays a role in regulating blood volume and blood pressure. 

Miller, H.R. (1987) Gastrointestinal mucus, a medium for survival and for elimination of parasitic nematodes and protozoa. Parasitology 94, S77-100. 

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