Permeability constants, percutaneous

Percutaneous absorption of hydroquinone from an aqueous solution was studied in full-thickness rat skin in vitro-, the permeability constant was 2.3 x 10 cm/h, which was approximately two-fold faster than that of human skin (Barber et al., 1995). 

Bemstam et al. (2002) measured percutaneous absorption of As(lll) and As(V) in vitro using artificial human skin. The permeability constant (K ) for As(V) and As(lll) were determined from this study as 4.3 x 10 cm/h and 10.1 x 10 cm/h respectively. As(lll) at exposure doses as low as 10 /zg/L could cause significant morphological changes, disruption of cell membrane and inhibition of deoxyribonucleic acid (DNA) and protein syntheses. The authors noted that concentrations of tri- or pentavalent arsenic at levels above 100 /zg/L in showering- or hand-washing waters could manifest harmful effects. 

Percutaneous absorption studied in vitro is normally characterized either by a permeability constant or by the time course of the penetration process. Direct measurements of absorption require intermittent sampling of fluid contained in the receptor half of a diffusion cell. Permeability constants are frequently calculated by removing and assaying microaliquots of receptor fluid at various intervals during the early time course of absorption ( static" diffusion cell technique), until steady state (ss) flux is obtained the permeability coefficients are then derived according to Pick s First Law of Diffusion ... 

Other characteristics, which influence percutaneous absorption, are solvent concentration gradients, solvent partitioning (water/lipid partition coefficient) and permeability constants. 

Other aspects of formulation such as the nature of the binary or ternary vehicle (oil-surfactant, water-surfactant or oil-water-surfactant, respectively) have been considered recently [151], Addition of polysorbate 80 to the aqueous phase has no significant effect on the epidermal transport of ethanol, but a significant reduction in the transport of the less soluble octanol results, in line with the arguments presented above in isopropyl myristate, octanol transport is not affected by the solubilizer while that of ethanol is decreased. In the ternary systems identified in Fig. 7.35, the results in Table 7.14 were obtained indicating a general decrease in permeability constants for ethanol, butanol and octanol. The viscosity of the vehicles was not a factor although this varied from 1 to 39 X 10 cP. In the ternary systems a surfactant will distribute itself between the aqueous and non-aqueous phase quantitative prediction of permeation is made difficult even with data on the transport properties of the permeants in the individual phase. The results indicate that the percutaneous absorption of the... 

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