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The transient absorption of two skin care agents, niacinamide (nicotinamide, NA) and methyl nicotinate (MN), solvent-deposited on ex vivo human skin mounted in Franz diffusion cells has been analyzed according to a new variation on a recently published mechanistic skin permeability model (Yu et al. 2020. J Pharm Sci 110:2149-56). The model follows the absorption and evaporation of two components, solute and solvent, and it includes both a follicular transport component and a dissolution rate limitation for high melting, hydrophilic solids deposited on the skin. Explicit algorithms for improving the simulation of transient diffusion of solvent-deposited solids are introduced. The simulations can account for the ex vivo skin permeation time course of both NA and MN over a dose range exceeding 4.5 orders of magnitude. The model allows one to describe on a mechanistic basis why the percutaneous absorption rate of NA is approximately 60-fold lower than that of its lower melting, more lipophilic analog, MN. It furthermore suggests that MN perturbs stratum corneum barrier lipids and increases their permeability while NA does not, presenting a challenge to molecular modelers engaged in simulating biological lipid barriers. [ABSTRACT FROM AUTHOR]

Fuller's earth (FE) is a phyllosilicate used as a powder for household or skin decontamination due to its adsorbent properties. Recent studies have shown that water suspensions exhibit similar adsorbent capacities. FE is heterogeneous due to its composition of elementary clay aggregates and heavy metal particles. Here, FE toxicity was assessed in vitro on skin cells and in vivo on Danio rerio embryos. Among the suspensions tested (5%, 9.1% and 15% w/w), only the highest one shows weak toxicity. Suspensions were tested for ex vivo dermal decontamination into pig ear skin and human abdominal skin using diffusion cells and paraoxon as organophosphorus contaminant. After 24 h of diffusion, no difference was observed in the paraoxon concentration in the receptor compartment whether the decontamination was carried out with FE in powder or in suspension form. In presence of FE suspensions, we observed the disappearance of paraoxon from the stratum corneum, the reservoir compartment, independently of the suspensions' concentration. We suggest that water potentiates the absorbing capacities of FE powder by intercalating between clay lamellas leading to the appearance of new adsorption zones and swelling. These data support the use of FE aqueous suspensions as a safe tool for organophosphorus skin decontamination. [Display omitted] • Fuller's earth is non-toxic in vitro and in vivo. • Increase of the decontamination efficiency not related to the clay concentration. • Water drags the contaminant deeper into the pores of the Fuller's earth. • Pig ear skin as cheap predictive model for human skin contamination with paraoxon. [ABSTRACT FROM AUTHOR]