0000000000869294
AUTHOR
M. Herráez
Influence of shear rate and concentration ratio on viscous synergism. Application to xanthan—Iocust bean gum— NaCMC mixtures Influencia de la velocidad de cizalla y la relación de concentraciones en la sinergia viscosa. Aplicación a mezclas de xantana-garrofín-CMCNa
A method is described that allows the development of an empirical approach to quantify synergistic interactions and their variations with shear rate. The approach is based on the definition of a viscous synergism index, Iv. The method is applied to xanthan-locust bean gum gels, and an equation is developed for relating the synergism index to shear rate, γ, and the locust bean gum/xanthan gum concentration ratio, z. The value of at which that function has a maximum, IMV, is calculated. This value of z provided an estimation of the proportion of gums at which maximum synergism occurs. A decreasing exponential dependence of these IMV on γ is shown. The influence of the addition of a fixed pro…
Comparative enhancer effects of Span20 with Tween20 and Azone on the in vitro percutaneous penetration of compounds with different lipophilicities.
Sorbitan monolaurate (Span20) was used in this study to analyze the influence of the polar functional group on the effects that non-ionic surfactants have on skin permeability. Its ethoxylate derivative polysorbate 20 (Tween20) and Azone, both with the same C12 alkyl chain as Span20, were used for comparative purposes. We evaluated the relative potency of the three molecules as enhancers in the permeability of a series of compounds with lipophilicities ranging from log Poct=-0.95 to log Poct=2.33. The influence of the enhancer concentration was also studied. For this purpose the epidermis of Wistar rat was pretreated with ethanolic solutions (1 and 5%, w/v) of each enhancer. Our results ind…
A solid-phase extraction and size-exclusion liquid chromatographic method for polyethylene glycol 25 p-aminobenzoic acid determination in urine: Validation for urinary excretion studies of users of sunscreens
No previous publications about percutaneous absorption of polyethylene glycol 25 p-aminobenzoic acid (PEG-25 PABA) have been found in the literature and the expected levels to be found in human urine after sunscreens use are unknown. The method proposed here is suitable to determine PEG-25 PABA in the urine of sunscreens users in order to carry out studies on body accumulation/excretion. It is based on solid-phase extraction (SPE) with size-exclusion liquid chromatography determination. Solid-phase extraction allows the analyte to be retained and subsequently eluted for a clean-up, using a silica-based cartridge. The size-exclusion liquid chromatography of the eluted allows the rest of matr…
Skin permeation model of phenyl alcohols: comparison of experimental conditions
Abstract This study was conducted primarily to establish the significance of the experimental conditions in the determination of permeability coefficients. In order to do this, standard in vitro skin permeation methods were used to determine the permeability coefficient (kp) of a homologous series of phenyl alcohols, with a wide range of lipophilicity, by two different experimental conditions through rat skin; first, using solutions (at 75% saturation concentration) of the penetrants in the donor compartment and second using saturated solutions added with an excess of the penetrant. The kp values obtained by these techniques were compared. Solubility of the phenyl alcohols in the donor phas…
A modelistic approach showing the importance of the stagnant aqueous layers in in vitro diffusion studies, and in vitro-in vivo correlations
Abstract The present study deals with the role of the aqueous diffusion layers on the in vitro penetration of xenobiotics across artificial lipoidal membranes, and their ability to reproduce biophysical absorption models when in vivo results are to be simulated from the in vitro tests. The aqueous boundary layers which are invariably formed on artificial lipoidal membranes can be optionally preserved or disrupted, according to the type of absorption site which should be simulated, a condition which could reasonably lead to a better correspondence between in vitro and in vivo results; in practice, disruption of water layers can be easily achieved by a synthetic surfactant solution at its cri…