Permeability comparative data

The logk obtained by MEKC, MEEKC and LEKC were also compared with membrane permeability reference data by Ornskov et al. [92]. An improved correlation was obtained in the order MEKC>MEEKC>LEKC. Thus, LEKC appears to provide experimental conditions that mimic more closely physiological membranes [93], However, liposomes and vesicles remain unstable and difficult to prepare reproducibly. Their use is then devoted to some parhcular applicahons. 

Table 8—Permeability rate of propranolol hydrochloride from Methocel matrix diffusion study through hairless mouse skin (comparative data)...

Table V. Comparative Permeability Rate Data - WEC Vs Vendor...

The insoluble cellulose derivatives utilized for permeation control of various species (e.g. oxygen and water vapor transport in coated pharmaceuticals, contact lenses, packaging, or water and solute transport through semi-permeable membranes in reverse osmosis, as well as drug release from reservoir systems) differ considerably in their permeability characteristics according to the type and extent of substitution, as well as their molar mass. However, very few comparative data are available from the literature on the polymers actually used in biological applications. Recently, new results have been published. Thus, Sprockel et al. [142] determined the water vapor transmission through various CA, CAT, CAB and CAPr films at different relative humidities (Table 22). 

Figure 15.1 to Figure 15.6 bear many similarities to comparable plots of human skin permeability coefficient data (Vecchia and Bunge, 2002b). It is not surprising that skin from different terrestrial species has similar characteristics of dermal penetration. Several mechanistic trends are consistently observed and also make good chemical sense ... 

The results were compared with the oxygen diffusion, solubility, and permeability coefficients obtained for PET films under the same conditions. The water sorption isotherm for polylactide films was also determined. Diffusion coefficients were determined with the half-sorption time method. Also, a consistency test for continuous-flow permeability experimental data was run to obtain the diffusion coefficient with the lowest experimental error and to confirm that oxygen underwent Eickian diffusion in the polylactide films. The permeability coefficients were obtained from steady-state permeability experiments. The results indicated that the polylactide films absorbed very low amounts of water, and no significant variation of the absorbed water with the... 

As expected, the estimated values were found to be closer to the correct ones compared with the estimated values when the water-oil ratios are only matched. In the 2nd run, the horizontal permeabilities of layers 5 to 10 (6 zones) were estimated using the value of 200 md as initial guess. It was found necessary to use the pseudo-inverse option in this case to ensure convergence of the computations. The initial and converged profiles generated by the model are compared to the observed data in Figures 18.25a and 18.25b. 

One of the key parameters for correlating molecular structure and chemical properties with bioavailability has been transcorneal flux or, alternatively, the corneal permeability coefficient. The epithelium has been modeled as a lipid barrier (possibly with a limited number of aqueous pores that, for this physical model, serve as the equivalent of the extracellular space in a more physiological description) and the stroma as an aqueous barrier (Fig. 11). The endothelium is very thin and porous compared with the epithelium [189] and often has been ignored in the analysis, although mathematically it can be included as part of the lipid barrier. Diffusion through bilayer membranes of various structures has been modeled for some time [202] and adapted to ophthalmic applications more recently [203,204]. For a series of molecules of similar size, it was shown that the permeability increases with octa-nol/water distribution (or partition) coefficient until a plateau is reached. Modeling of this type of data has led to the earlier statement that drugs need to be both... 

Figure 6 Correlation of the fraction of dose absorbed with Caco-2 cell permeability obtained in four different laboratories ( , , A, and A). Qualitatively similar correlations were established in all four laboratories, but the data are not directly comparable due to quantitative differences in the permeability of the Caco-2 monolayers. (From Ref. 38 with kind permission from Elsevier Science-NL, Amsterdam.)...

The first set of data is for oil production from 22 wells. A quaternary ammonium salt polymer clay stabilizer was utilized in five of the well treatments. Otherwise the 22 well treatment designs were identical. Use of the clay stabilizer in 5 well treatments resulted in a 131% production increase compared to a 156% increase after stimulation of 17 wells without clay stabilizer. Although the initial overall production response of the five clay stabilizer treated wells was less, the overall production decline rate was 4% per year compared to 16%/yr for the treatments which did not include the clay stabilizing polymer. This decline rate was determined for the period 4 to 24 months after well treatment. It is tempting to speculate that the lower initial production response of the five polymer treated wells was due to the formation of an adsorbed polymer layer which reduced formation permeability (particularly of the Wilcox Formation) significantly. 

Figure 3.6 compares iso-pH permeabilities of ketoprofen at various pH values in a 2% DOPC-dodecane model (open circles) and the 20% soy lecithin with SLS in the acceptor compartment (filled circles, data in Table 3.5). In the presence of the latter negatively charged lipids (with the make-up similar to that of BBM in Table 3.1), ketoprofen is intrinsically more permeable, by a factor of 17. The UWL limit, indicated by the solid curves in low-pH solutions, and consistent with the permeability Pu 19.8 x 10-6 cm s 1 (log Pu —4.7), masks the true intrinsic permeability of the membranes, P0. However, it is possible to deduce the membrane permeability if the pKa is known. In Fig. 3.6, the bending in the dashed (calculated) curves at pH 4 corresponds to the pKa of the molecule. Due to the UWL, the point of bending is shifted to higher pH values in the solid (measured) curves. The difference between the apparent pKa (pK 5.3 for DOPC and 6.3 for soy) and the true pKa (4.12) is the same as the difference between log P0 and log Pu [23],... 

When comparing different experimental sources of Caco-2 permeability data, quantitative comparison is almost impossible, due to intervariations of experimental procedures between laboratories, although standard protocols and reference molecules are often used. 

Factors influencing the production and migration of radon in soils have been examined, and various sources of geographic data have been discussed. Two significant soil characteristics include air permeability and, less importantly, radium concentration. While there are, at present, few opportunities to compare the larger-scale data with on-site field measurements, those comparisons that have been made for both surface radium concentrations and air permeability of soils show a reasonable correspondence. Further comparisons between the aerial radiometric data and surface measurements are needed. Additional work and experience with SCS information on soils will improve the confidence in the permeability estimates, as will comparisons between the estimated permeabilities and actual air permeability measurements performed in the field. 

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