Ebook Predictive methods in percutaneous absorption: Part 2
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Ebook Predictive methods in percutaneous absorption: Part 2
Chapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2scussed in Chap. 2, there arc a range of established and validated in vitro methods for the measurement of percutaneous absorption. In general, in vitro experiments of the nature described in Chap. 2 will form a significant part of early-Slage evaluation of pharmaceutical formulations or in risk ass Ebook Predictive methods in percutaneous absorption: Part 2essment protocols. Their use is followed by. and informs, preclinical and clinical evaluation. While fresh human skin (either as full thickness skin,Ebook Predictive methods in percutaneous absorption: Part 2
heat-separated epidermal tissue or skin dermatomed to a defined thickness) is the perceived “gold standard’’ for in vitro testing, it is not always avChapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2ckwards” from the idealised in vitro model leads to the use of animal tissue; while the use of tissue from a range of species (rat, mouse, pig, guinea pigs, snakes and various species of monkey) has been widely reported in the literature, it is accepted that pigskin is (he best model for human skin, Ebook Predictive methods in percutaneous absorption: Part 2 w ith the pig car being widely used despite differences in the lateral packing of stratum comeum lipids and suggestions that it may have a lower barrEbook Predictive methods in percutaneous absorption: Part 2
ier function than human skin (Pctitot Ct al. 2007; Vallet et al. 2007; Caussin et al. 2008; Klang et al. 2012). In order to address the issue of tissuChapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2gy includes marketed products such as EpiDerm®, EpiSkin' and SkinEthic®. Reconstructed skin models have also been considered although they have been found to exhibit higher permeability than excised mammalian skin as they often have an incomplete or inconsistent barrier (Van Gclc Ct al. 2011; Kuchlc Ebook Predictive methods in percutaneous absorption: Part 2r Ct al. 2013). In general, their use has not become widespread, and they have a peripheral role in the models of skin absorption (Netzlaff et al. 200Ebook Predictive methods in percutaneous absorption: Part 2
5; Schafer-Korting Ct al. 2008).€> Springer-Verlag Berlin Heidelberg 2015G.p. Moss et al.. Predictive Methods in Percutaneous Absorption.DOI 10.1007/9Chapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2artificial membranes have found widespread use in early-stage assessment of percutaneous absorption. Il is not the aim of this chapter to review these studies, but a few examples are given below, and present an important context for consideration of model development. For example, Ahmed et al. (1983 Ebook Predictive methods in percutaneous absorption: Part 2) characterised phenothiazinc transport across liquid—lipid, phospholipid and soft polymer membranes. Feldstein el al. (1998) carried out a comparativEbook Predictive methods in percutaneous absorption: Part 2
e study of human skin permeability and permeability across a “skin-imitating” PDMS-polycarbonate block copolymer (Carbosil"'). They used a group of 14Chapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2teristics as human skin for their 14 penetrants. In a similar study, Shumilov et al. (2009) also evaluated a biphasic artificial membrane. However, neither membrane has found widespread use.Woolfson et al. (1998) examined a range of tetracaine formulations and investigated their penneation across a Ebook Predictive methods in percutaneous absorption: Part 2PDMS (SilasticR) membrane. They commented that, in cases where the lipophilicity of the penetrant was the prime determinant of drug flux, which is theEbook Predictive methods in percutaneous absorption: Part 2
case for the lipophilic local anaesthetic tetracaine (ameth-ocainc). PDMS membranes had been shown to produce good correlations with the in vivo situChapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2n’s 1998 study also correlated reasonably well with a later study using porcine skin (Moss Ct al. 2006). Other studies, for example Khan cl al. (2005) and Kumprakob Ct al. (2005), also used silicone membranes to assess drug delivery, with the former study comparing permeability across a silicone mem Ebook Predictive methods in percutaneous absorption: Part 2brane to pigskin permeability and observing significant differences in the distribution of the permeability across both membranes. Wasdo et al. (2009)Ebook Predictive methods in percutaneous absorption: Part 2
also found correlations between PDMS and mammalian skin permeability, developing a scries of models to quantify their findings for a 32-membcr data sChapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2veral researchers have used artificial membranes, mostly poly-dimcthylsiloxane (PDMS), to investigate the mechanisms of membrane transport (Waktinson et al. 1994; Pellett et al. 1994). Ley and Bunge (2007) used PDMS membranes to compare permeation from finely divided pure powder and saturated aqueou Ebook Predictive methods in percutaneous absorption: Part 2s solutions of model penetrants and examining the role of surface coverage in particular. Dias Ct al. (2007) used PDMS membranes to compare the releasEbook Predictive methods in percutaneous absorption: Part 2
e characteristics of saturated solutions due to their homogeneity and uniformity, compared to mammalian skin. They found that permeability was relatedChapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2in their permeation rates) and that the solvents were taken up into the membrane, altering its properties and the flux of the permeants. They concluded that membrane flux is governed by a combination of solvent and solute characteristics, including size, shape and charge distribution. ATR-FTIR spect Ebook Predictive methods in percutaneous absorption: Part 2roscopy was used to evaluate diffusion across a PDMS membrane (McAuley et al. 2009). Diffusion was described by a FickianThe Role of Artificial MembraEbook Predictive methods in percutaneous absorption: Part 2
nes in Studies of Percutaneous Absorption93model, and it was determined that the three model chemicals examined—cyanophenol. methyl nicotinate and butChapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2 isostearate was observed. The relative diffusion rates of the different permeants were generally attributed to molecular size. McAuley et al. (2010) also developed a rudimentary structure-activity relationship for permeability across a PDMS membrane. Olivera et al. (2010) also used a thermodynamic Ebook Predictive methods in percutaneous absorption: Part 2and kinetic analysis of temperature-dependent PDMS diffusion to elucidate the possible mechanisms of transport. They found a break point for butanol wEbook Predictive methods in percutaneous absorption: Part 2
hich appeared to differentiate mechanisms of solute diffusion and partitioning which was potentially associated with temperature-induced changes in thChapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2erms of their physicochemical properties) range of prodrugs of captopril, characterising their permeability across pigskin and a PDMS membrane. They found a biphasic relationship between molecular properties (notably log p and MW) where skin permeability increased with increases in log p and MW and Ebook Predictive methods in percutaneous absorption: Part 2then decreased for larger, lipophilic molecules. In significant contrast, permeability across the Silastic" membrane increased exponentially as log pEbook Predictive methods in percutaneous absorption: Part 2
and MW were increased. P(Mir correlations were therefore found between the Silastic* membrane and pigskin permeability. This sits somewhat at odds witChapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2et al., compared to the majority of other studies which used narrower molecular spaces in making their comparisons. In most cases, comparisons were made for membrane permeability for one chemical or a scries of similar chemicals, such as drugs in a similar therapeutic class.From Ct al. (2007) used f Ebook Predictive methods in percutaneous absorption: Part 2ive model penetrants to examine the normal distribution of permeability coefficients across a PDMS membrane. Their findings—that the permeability coefEbook Predictive methods in percutaneous absorption: Part 2
ficients of all five drugs were distributed in a Gaussian-normal fashion—arc in contrast with those reported for mammalian skin, which were found to bChapter 5Algorithms for Estimating PermeabilityAcross Artificial MembranesThe Role of Artificial Membranes in Studies of Percutaneous AbsorptionAs dis Ebook Predictive methods in percutaneous absorption: Part 2atkinson et al. 199X; Roper et al. 2000; Fasano et al. 2002; Khan et al. 2005; Wenkers and Lippold 1999), in which log-normal patterns were common. They attributed this difference to the heterogeneity of biological membranes, including the possibility of multiple permeation pathways in mammalian ski Ebook Predictive methods in percutaneous absorption: Part 2n, which is in stark contrast to the homogeneity of PDMS, and similar, membranes.Therefore, while significant limitations have been identified in theEbook Predictive methods in percutaneous absorption: Part 2
use of such membranes (i.c. Moss Ct al. 2006). artificial membranes can provide an effective screen in early-stage formulation development, and givenGọi ngay
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