Permeability and stability

The interaction of such compounds with the bilayer can result in alteration in vesicle properties such as permeability and stability of the bilayer structure. Amphiphatic compounds such as detergents (e.g., Triton and lysophosphoiipids) can intercalate in the bilayer below their critical micelle concentration (CMC) (Kitagawa et al.,... 

Mectianism of Action An adrenocorticosteroid that controls the rate of protein synthesis, depresses migration of polymorphonuclear leukocytes, reverses capillary permeability, and stabilizes lysosomal membranes. Therapeutic Effect Prevents or controls inflammation. 

In particular, the transition temperature also influences the physical parameters, such as permeability and stability (liposomes can only be prepared at temperatures above Tm), and the encapsulation of solutes is rather low below this temperature (Janiak et al, 1976 Machy and Leserman, 1987 Gennis, 1989). 

The rate and extent of absorption of drug Y will be a function of its solubility, intestinal permeability, and stability in the gastrointestinal fluids and dissolution rate. Differences in the absorption of two phannaceutically equivalent products should then primarily be a function of their in vivo dissolution rate differences, assuming the excipients used do not alter bioavailability [38]. Therefore, the key question here is Does an in vitro dissolution test emulate in vivo drug dissolution ... 

Quinn, P. J., and Cherry, R. J., eds. (1992) Structural and Dynamic Properties of Lipids and Membranes, Portland Press, London Disalvo, E. A., and Simon, S. A., eds. (1995) Permeability and Stability of Lipid Bilayers, CRC Press, Boca Raton, Florida Jacobson, K., Sheets, E. D., and Simson, R. 

Lindbrathen A and Hagg MB. Glass membranes for purification of aggressive gases. Part I Permeability and stability. J. Membr. Sci. Accepted for publication January 2005. 

In vitro experiments can sometimes provide valuable insight into what is happening in vivo that is limiting oral bioavailability. The typical experiments, often employed in tandem, to understand bioavailablilty are determinations of compound solubility, membrane permeability, and stability in subcellular fractions. The membrane permeability assays that are most often employed are either a measurement of permeability through an artificial membrane (Parallel artificial membrane permeability assay, PAMPA, is the most common technique) or a cell monolayer (Caco-2, a human colon carcinoma-derived cell line, is the most common cell monolayer). The subcellular fractions most often employed are plasma (for ester-containing compounds) and liver microsomes with the addition of either reduced nicotinamide adenine dinucleotide phosphate (NADPH) or uridine diphosphoglucuronic acid (UDPGA) as cofactor. 

In selecting the most appropriate membrane, a much wider choice is available for polymeric than for either metallic or ceramic membranes. Polydi-methylsiloxane (PDMS) is by far the most commonly used, thanks to its high permeability and stability. Polyvinylalcohol (PVA) and Nation have also been described, especially for the more hydrophilic substrates. Operation of a polymer based MR at relatively... 

When inadequate in vivo exposure or PK properties are observed, pharmaceutical profiles can be used to troubleshoot the cause of poor in vivo exposure or PK [26]. Assays for solubility, permeability, and stability (metabolic, plasma, acid) can help to track down the inadequate properties responsible for poor in vivo performance. Property optimization synthesis can then be initiated. Subsequent series analogs can be assayed to rank order compounds by properties for subsequent in vivo tests, in order to give the highest likelihood of success. Often animal studies are expensive and time-consuming, especially if they are performed using the animal activity model. Simple in vitro profiling assays can provide information for improved decisions and efficiency. 

Lucy, J.A. (1972) Functional and structural aspects of biological membranes a suggested role for vitamin E in the control of membrane permeability and stability. Ann. N. Y. Acad. Set. 203 4-11. ... 

Kovalevsky, A.V., Yaremchenko, A.A., Kolotygin, V.A. et al. (2011) Oxygen permeability and stability of asymmetric multilayer Ba0.5Sr0.5Co0.8Fe0.2O3 ceramic membranes. Solid State Ionics, 192, 677-681. 

Palladium or its alloys are the most practical membrane materials, due to their high hydrogen permeability and stability at high temperatures. The membrane reformer is composed of a steam reformer equipped with palladium-based alloy modules in its catalyst bed, and can perform steam reforming reaction and hydrogen separation processes concurrently with no help from shift converter and PSA, as shown in Fig. 12.1. 

Palladium was applied for manufacturing the membrane reactor for dehydrogenation of cyclohexane in early studies. Palladium membranes face some weaknesses in terms of cost, permeability, and stability (Itoh Haraya, 2000). Recentiy, the performance of... 

Cafiso DS (1995) In Disalvo EA, Simon SA (eds) Permeability and Stability of Lipid Bilayers. CRC Press, Boca Raton, Florida... 

Their applications and improved long-term stability for gas separation and pervaporation were further investigated. A maximum in the separation factor and rate was obtained for the PTMSP copolymer with 12 mol% PDMS. The membrane was able to convert a 7 wt% ethanol mixture to over 70 wt% in ethanol [120]. Good oxygen permeability and stability of over a month was also achieved for the PTMSP copolymers with over 60% PDMS [121]. In a separate study, PPP was foimd to have good permselectivity to water while PTMSP is alcohol permselective. These copolymers as well as a series of poly(phenyl acetylene) graft PTMSP copolymers were further studied for pervaporation applications [122]. 

Tribet, C., and Vial, F. 2008. Flexible macromolecules attached to lipid bUayers Impact on fluidity, curvature, permeability and stability of the membranes. Soft Matter A 68. 

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