Bio-availability

Tocainide is rapidly and well absorbed from the GI tract and undergoes very fitde hepatic first-pass metabolism. Unlike lidocaine which is - 30% bioavailable, tocainide s availability approaches 100% of the administered dose. Eood delays absorption and decreases plasma levels but does not affect bio availability. Less than 10% of the dmg is bound to plasma proteins. Therapeutic plasma concentrations are 3—9 jig/mL. Toxic plasma levels are >10 fig/mL. Peak plasma concentrations are achieved in 0.5—2 h. About 30—40% of tocainide is metabolized in the fiver by deamination and glucuronidation to inactive metabolites. The metabolism is stereoselective and the steady-state plasma concentration of the (3)-(—) enantiomer is about four times that of the (R)-(+) enantiomer. About 50% of the tocainide dose is efirninated by the kidneys unchanged, and the rest is efirninated as metabolites. The elimination half-life of tocainide is about 15 h, and is prolonged in patients with renal disease (1,2,23). 

Molybdenum because of its unique chemical versatility and unusually high bio-availability has been incorporated widely into biological systems. It is the only second-row transition metal that is essential for most of living organisms and belongs to elements (along with Cu, Cd, Hg, Pb and Cr) potentially hazardous to humans. 

UPTAKE AND BIO AVAILABILITY OP PERSISTENT ORGANIC POLLUTANTS BY PLANTS GROWN IN CONTAMINATED SOIL... 

The above description of eutrophication has illustrated the complex nature of the problem, particularly in relation to the influence of nutrients, the multiplicity of sources of phosphorus and the spectrum of its bio-availability. Clearly, the most effective long-term solution to many of our eutrophication problems will be to reduce the nutrient load to affected waters. However, it has also been shown that, because the concentrations of available phosphorus required to impose a control on primary production is very low (e.g. 5-10/rgU total dissolved phosphorus), the reduction of nutrients from any one source alone is unlikely to be effective. 

Bioavailability is defined as the portion or fraction of a chemical that is available for biological action and is influenced by several factors including the molecular size and charge of a molecule, structural features of membranes, first pass metabolism, and therefore, bio availability can be influenced by the molecular structure of a chemical. This situation presents an opportunity for molecular designers to manipulate a chemical s structure to decrease bioavailability and consequently hazard. If the availability of a molecule can be decreased, the amount of chemical at the site of action is decreased which leads to decreased toxicity. 

Dorr P, Westby M, Dobbs S, et al. Maraviroc (UK-427,857), a potent, orally bio-available, and selective small-molecule inhibitor of chemokine receptor CCR5 with broad-spectrum anti-human immunodeficiency virus type 1 activity. Antimicrob Agents Chemother 2005 49 472 l —4732. 

C.-S. You, R. S. Parker, and J. E. Swanson, Bio availability and vitamin A value of carotenes from red palm oil assessed by an extrinsic isotope reference method, Asia Pac. J. Clin. Nutr. 11 (2002) S348-S442. 

The bioavailability of trace elements in soil-water-plant ecosystems of arid zones is largely determined by their partitioning between solution and solid-phase components. The redistribution and transformation of trace elements among solid-phase components under various biogeochemical conditions strongly adjust their lability and bioavailability. Soluble, exchangeable and organically bound forms are bioavailable to plants. The carbonate bound fraction represents a reservoir of potentially bio-available trace elements to plants. In paddy soils, the amorphous Fe/Al oxide fraction contributes to trace element availability as well. 

Ehlers GAC, Loibner AP (2006) Linking organic pollutant (bio)availability with geosorbent properties and biomimetic methodology A review of geosorbent characterization, and (bio)availability prediction. Environ Pollut 141 494-512... 

Stolzberg [143] has reviewed the potential inaccuracies of anodic stripping voltammetry and differential pulse polarography in determining trace metal speciation, and thereby bio-availability and transport properties of trace metals in natural waters. In particular it is stressed that nonuniform distribution of metal-ligand species within the polarographic cell represents another limitation inherent in electrochemical measurement of speciation. Examples relate to the differential pulse polarographic behaviour of cadmium complexes of NTA and EDTA in seawater. 

It was determined that 9.5% of an oral 80-mg dose of verapamil was absorbed in a 70-kg test subject. However, because of extensive bio transformation during its first pass through the portal circulation, the bio availability of verapamil was only 25%. Assuming a liver blood flow of 1500 mLAmin, the hepatic clearance of verapamil in this situation was... 

Soldier crabs (Mictyris longicarpus) accumulate copper mostly from sediments rather than the water column (Weimin et al. 1994). The fine particles of sediment trapped as food contain bio-available fractions of copper and other metals, and these significantly correlate with metal concentrations in the body of the crab. However, copper accumulations from sediments by soldier crabs... 

Fouchecourt, M.O., P. Berny, and J.L. Riviere. 1998. Bio availability of PCBs to male laboratory rats maintained on litters of contaminated soils PCB burden and induction of alkoxyresorufin O-dealkylase activities in liver and lung. Arch. Environ. Contam. Toxicol. 35 680-687. 

Strategies for reducing risk to the infant from drug transferred through breast milk include selection of medications for the mother that would be considered safe for use in the infant choosing medications with shorter half-lives selecting those that are more protein bound, have lower bio-availability, and have lower lipid solubility. 

Nevertheless, their potential use in large treatments will depend on systemic actions, since the beneficial effects may be counterbalanced by deleterious consequences on the cardiovascular (Hegele-Hartung et al. 1997) and skeletal systems (Gallagher et al. 1993). Moreover, most pure antiestrogens have a poor oral bio availability. Therefore, the use of other routes of administration, such as intravenously, is mandatory. In some cases, to circumvent such problems, the production of nanospheres loaded with the pure antiestrogen RU 58668 has been tested (Ameller et al. 2004). 

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