Partitioning characteristics

Drugs that are too highly hydrophilic are often absorbed rather poorly from the gastrointestinal tract. It is sometimes possible to circumvent this difficulty by preparing esters of such compounds so as to change their water lipid partition characteristics in order to enhance absorption. Once absorbed, the esters are cleaved by the numerous esterase enzymes in the bloodstream, releasing free drug. 

At the fundamental level of equilibrium modeling the advantages are many. The model can combine a number of compartments through simple relationship to describe a realistic environment within which chemicals can be ranked and compared. Primary compartments that chemicals will tend to migrate toward or accumulate in can be identified. The arrangement of compartments and their volumes can be selected to address specific environmental scenarios. Data requirements are minimal, if the water solubility and vapor pressure of a chemical are known, other properties can be estimated, and a reasonable estimate of partitioning characteristics can be made. This is an invaluable tool in the early evaluation of chemical, whether the model be applied to projected environmental hazard or evaluation of the behavior of a chemical in an environmental application, as with pesticides. Finally, the approach is mathematically very simple and can be handled on simple computing devices. 

When high-specific-activity, non-colloidal preparations are administered (a) they are partitioned characteristically between liver and bone (b) in rodents the rate of loss of the liver burden is high (halftime = 6.5 to 10.8 d) (Durbin, 1973) (c) the spleen content is low and (d) autoradiographs show uniform distribution in hepatic cells rather than of phagocytosis of radioactive particles in the reticuloendothelial cells of the liver, spleen, and bone marrow, and there is deposition on bone surfaces. 

Chiou C, McGrody S, Kile D (1998) Partition characteristics of polycyclic aromatic hydrocarbons on soils and sediments. Environ Sci Technol 1998 264-269... 

The studies on phospholipid bilayers with defined amounts of charged component are helpful to explain the partition characteristics in biological membranes. Liposome water partition data of propranolol in lipids from kidney epithelial cells (a common model system in pharmaceutical sciences for the uptake into the gastrointestinal tract) have been successfully described with partition models developed for pure bilayers or defined mixtures [159]. Since lipophilic cations and anions can be used as probes for the membrane potential, their interaction with microbial and mitochondrial membranes has been studied... 

Absorption of chemicals with widely differing characteristics can occur at different levels in the GI tract (Schranker, 1960 Hogben et al., 1959 Schranker et al., 1957). The two factors primarily influencing this regional absorption are (1) the lipid-water partition characteristics of the undissociated toxicant and (2) the dissociation constant (pLJ that determines the amount of toxicant in the dissociated form. 

Equations 2.109 and 2.111 illustrate that the required number of plates will depend on the partition characteristics of the column and the relative volatility of the two components, that is on K and 3. Table 2.9 gives the values of the last term of Equation 2.109 for various values of k. These data point up a few interesting conclusions If k <5 the plate numbers are controlled mainly by column parameters if k >5 the plate numbers are controlled by relative volatility of components. The data also illustrate that k values greater than 20 cause theoretical number of plates, n, and effective number of plates, N, to be of the same order of magnitude, that is,... 

What is the physicochemical and pharmacological nature of the penetrant The drugs to be delivered should be considered in relation to its polarity and partition characteristics, molecular weight and size, in respect of either water-based or more hydrophobic systems. 

Chiou, C.T., McGroddy, S. E., and Kile, D. E. (1999). Partitioning characteristics of polycyclic aromatic hydrocarbons on soil and sediments. Environ. Sci. Technol. 33, 2390-2394. 

Outputs from the LSC must be corrected for background radiation and counting efficiency. The parts-per-million (ppm) equivalent to the radioactive chemical in a biological, soil or water sample can then be determined by accounting for aliquot size, specific activity, and other correction factors specific for the sample. Partitioning characteristics and chromatographic data can be treated in a like manner. Although many... 

In order to increase the number of drugs which can be administered transdermally, the barrier function of the skin must be reduced. The kinetic model can be used to assess the role of a penetration enhancer as a function of the physicochemical properties of the drug. In its simplest form a penetration enhancer may be considered to act in one of two ways. Firstly it may increase the permeability of the skin and, secondly, it may additionally modify the partitioning characteristics at the stratum corneum-viable tissue interface. For illustration, two enhancers have been arbitrarily chosen, the first PE1 increases the permeability by a factor of 10, i.e. k- is increased ten fold. The second, PE2, increases k- by a factor of 10 and decreases kg by a similar amount. Thus PE2 additionally reduces the partition coefficient by a factor of 10. The relative effects can be seen by considering two model drug... 

Many factors including partition characteristics, degree of ionization, molecular size etc. influence the transport of drugs across biological membranes. Permeation of intact mucosa may also involve passive diffusion, intercellular movement, transport through pores or other mechanisms. The objective of the studies reported here was to employ the dog model to investigate these factors in a systematic and experimentally well-controlled fashion. The non-steriodal anti-inflammatory drug, diclofenac sodium, was selected as a test compound in this evaluation process. 

Estimate the polymer/liquid partition coefficient for cis-3-hexenol between a package with a LDPE material food contact layer. The package contains a food system whose partitioning characteristics can be simulated using 100 % ethanol at 25 °C. Use the UNIFAC activity coefficient estimation method and assume a dilute solution (x, = w, 0.00001). 

Table VI. Effect of 0.1% Tween 80 on Octanol/Water Partitioning Characteristics of TFMS Herbicides ...

TFMS derivative in the presence of surfactant (cf. also Figures 2a and 2c). Thus, the loss in Foxtail activity which results from the deleterious effect of surfactant on the pa term in the Hansch equation is compensated by the improved partitioning characteristics (large Bn term) of the 4-methylsulfonyl derivative in the presence of surfactant. The net result is that the overall pre-emergence Foxtail activity is not greatly affected by Tween 80. As illustrated in Table XIII, however, this effect is only apparent since significant changes in both ir and a dependence have taken place. 

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