Absorption gastrointestinal

Most of the absorption in the GIT is by passive diffusion, except for nutrients glucose, amino acids, and drugs that look like these substances are taken up by 

Crypts I Crypts Cross Sect. Lamina L Muscularis 

GIT motility has a significant effect on GIT absorption of a toxicant. For example, excessively rapid movement of gut contents can reduce absorption by reducing residence time in the GIT, while the presence of food in the stomach can delay the progress of drugs from the stomach to the small intestine where most of the absorption will occur. Increased splanchnic blood flow after a meal can result in absorption of several drugs (e.g., propranolol), but in hypovolemic states, absorption can be reduced. 

Both As(V) and As(III) are rapidly and extensively absorbed from the gastrointestinal tract of common laboratory animals following a single oral dose. Based on the mouse data of Vahter and Norin (1980), inorganic As(III) is more extensively absorbed from the gastrointestinal tract compared to inorganic As(V) at lower doses (e.g. 0.4 mg As kg-1), whereas the reverse is true at higher doses (e.g. 4.0 mg As kg-1)  

It is now clear that bioavailability varies with the form of Al. The chemical form of Al at the mucosal wall depends not only on the form ingested, but also on the pH, concentration of the dose, and the presence of dietary complexing factors such as citrate and F. Many experiments have been performed with soluble AICI3, which produces a low pH solution. If the pH is then raised, artificially or physiologically during entrance into the intestine, insoluble aluminum hydroxide will form unless alternative ligands 

While much has been written on variability of absorption with pH of the lumen or form of the Al administered (see reviews by Van der Voet 1992 De Voto and Yokel 1994), variability between laboratories is still greater than the variability caused by any of these factors For example, one laboratory reported 27% absorption of a dose of AICI3 given rats (Gupta et al. 1986), while another reported less than 1% for a similar dose of the same compound under similar conditions of acidity to the same species (Ittel et al. 1987). Clearly, there are unrecognized varibles here which, when identified, may help us to understand why one patient can tolerate binding gel treatment, while another rapidly accumulates Al to neurotoxic levels. 

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Terazosin is selective a -adrenoceptor blocker having hypotensive efficacy equal to that of prazosin. Terazosin has a longer duration of action and better gastrointestinal absorption profile than prazosin. 

As in gastrointestinal absorption, the lipophillic nonionic form of a drug is more susceptible to reabsorption from the renal tubules by simple diffusion. Therefore,... 

Amino acids promote the production of proteins, enhance tissue repair and wound healing, and reduce the rate of protein breakdown. Amino acids are used in certain disease states, such as severe kidney and liver disease, as well as in TPN solutions. (See the last section of this chapter for a more detailed discussion of TPN.) TPN may be used in patients with conditions such as impairment of gastrointestinal absorption of protein, in patients with an increased requirement for protein, as seen in those with extensive bums or infections, and in patients with no available oral route for nutritional intake ... 

Glutethimide (3-ethyl-3-phenyl-2,6-piperidinedione) is a sedative-hypnotic drug that is now rarely used therapeutically because of wide variation in gastrointestinal absorption, fast development of pharmacodynamic tolerance, a fairly severe discontinuation syndrome, and potential for abuse. Reports of... 

Treatment of acute PCP intoxication includes efforts to decrease gastrointestinal absorption of the drug (e.g., by activated charcoal) and to increase renal... 

Noland EA, MeCauley PT, Bull RJ (1983) Dimethyltin dichloride Investigations into its gastrointestinal absorption and trans-plaeental transfer. Journal of Toxicology and Environmental Health. 12 89-98. 

Turekian, K.K. and Kulp, XL. 1956 Strontium content of human Bones. Science 124 405 107. Wasserman, R. and Comar, C.L. 1956 Carbohydrates and gastrointestinal absorption ofradiostron-tium and radiocalcium in the rat Proceedings of the Society for Experimental Biological Medicine 101 314-317. 

Octanol-water partition (log P) and distribution (log D) coefficients are widely used to make estimates for membrane penetration and permeability, including gastrointestinal absorption [77, 78], BBB crossing [60, 69] and correlations to pharmacokinetic properties [1]. The two major components of lipophilicity are molecular size and H-bonding [57], which each have been discussed above (see Sections 2.5 and 2.6). 

Benzodiazepines are the evidence-based treatment of choice for uncomplicated alcohol withdrawal.17 Barbiturates are not recommended because of their low therapeutic index due to respiratory depression. Some of the anticonvulsants have also been used to treat uncomplicated withdrawal (particularly car-bamazepine and sodium valproate). Although anticonvulsants provide an alternative to benzodiazepines, they are not as well studied and are less commonly used. The most commonly employed benzodiazepines are chlordiazepoxide, diazepam, lorazepam, and oxazepam. They differ in three major ways (1) their pharmacokinetic properties, (2) the available routes for their administration, and (3) the rapidity of their onset of action due to the rate of gastrointestinal absorption and rate of crossing the blood-brain barrier. 

Oxazepam is available in oral form only, so it is useful only for uncomplicated withdrawal. Other benzodiazepines are available in injectable form and will be further described below. Diazepam and lorazepam are more lipophilic than chlordiazepoxide and oxazepam, resulting in quicker gastrointestinal absorption and passage across the blood-brain barrier, which makes them valuable in an inpatient setting, especially to treat or prevent seizures. However, their faster onset of action maybe associated with feeling high, which can be a disadvantage of their use. 

For example, elderly patients living in musing homes will not be able to meet vitamin D requirements and will need supplementation. Vitamin D deficiency is common in elderly patients owing to decreased exposure to sunlight and subsequent decreased vitamin D synthesis in the skin, decreased gastrointestinal absorption of vitamin D, and reduction in vitamin D3 synthesis. Individuals living in northern climates also have decreased exposure to sunlight and are less likely to achieve vitamin D requirements. 

Eisele GR, Bernard SR, Nestor CW. 1987. Gastrointestinal absorption of americium-241 by orally exposed swine Comparison of experimental results with predictions of metabolic models. Radiat Res 112 62-73. 

Ham GJ, Harrison JD, Popplewell DS, et al. 1994. The gastrointestinal absorption of neptunium, plutonium and americium in a primate (C. jacchus). Sci Total Environ 145 1-6. 

Harrison JD. 1991. The gastrointestinal absorption of the actinide elements. Sci Total Environ 100 43-... 

Harrison JD, Naylor GPL, Stather JW. 1994. The gastrointestinal absorption of plutonium and americium in rats and guinea pigs after ingestion of dusts from the former nuclear weapons site at Maralinga Implications for human exposure. Sci Total Environ 143 211-220. 

Naylor GPL, Haines JW, Whysall K, et al. 1993. Measurements of the gastrointestinal absorption and tissue distribution of plutonium, americium and polonium in experimental animals. Sci Total Environ 130 429-435. 

NEA. 1988. Gastrointestinal absorption of selected radionuclides. Paris Nuclear Energy Agency. 

Stather JW, Harrison JD, Rodwell P, et al. 1979a. The gastrointestinal absorption of plutonium and americium in the hamster. Phys Med Biol 24(2) 396-407. 

Sullivan MF, Gorham LS. 1983. Can information on the gastrointestinal absorption of actinide elements by neonatal rats, guinea pigs, dogs and swine be extrapolated to man Health Phys 44(Suppl. 1) 411-417. 

As mentioned previously, ingested food-grade mineral oil is absorbed only to a limited extent in humans and animals (Brunton 1985 Ebert et al. 1966). The physicochemical similarities between polyalphaolefins and mineral oils suggest that the extent of gastrointestinal absorption of polyalphaolefin hydraulic fluids also may be limited. 

Y Yoshimura, N Kakeya. Structure-gastrointestinal absorption relationship of penicillins. Int J Pharm 17 47-57, 1983. 

G Levy, BA Sahli. Comparison of the gastrointestinal absorption of aluminum acetylsalicylate and acet-ylsalicylic acid in man. J Pharm Sci 51 58-62, 1962. 

RG Crounse. Human pharmacology of griseofulvin. The effect of fat intake on gastrointestinal absorption. J Invest Dermatol 37 529-533, 1961. 

M Kraml, J Dubuc, D Beall. Gastrointestinal absorption of griseofulvin. I. Effect of particle size, addition of surfactants and corn oil on the level of griseofulvin in the serum of rats. Can J Biochem Physiol 40 1449-1451, 1962. 

KKH Chan, A Buch, RD Glazer, VA John, WH Barr. Site-differential gastrointestinal absorption of benazepril hydrochloride in health volunteers. Pharmaceut Res 11 432-437, 1994. 

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