RESUMEN

Tretinoin is used in the management of acne and it is part of a gold standard treatment for photoaging. It has also been reported as an agent for superficial chemical peeling in highly concentrated formulations with few considerations about skin penetration. The aim of this study was to evaluate the influence of drug concentration and vehicles currently used on skin penetration of tretinoin. In vitro permeation tests were carried out using Franz diffusion cells fitted with porcine ear skin and 10% aqueous methanol in the receptor compartment. Formulations studied, cream or hydroalcoholic dispersion, containing 0.25%, 1% and 5% of tretinoin were placed in the donor compartment for six hours. Tretinoin concentration in skin layers was measured by high performance liquid chromatography. The largest amount of tretinoin from both vehicles was detected in stratum corneum with significant differences among the three concentrations. The hydroalcoholic dispersion was the best vehicle. Significant amounts of tretinoin were found even in deep layers of epidermis. The formulation with 0.25% tretinoin showed better results when considered the amount of tretinoin on skin in terms of percentage. Finally, skin penetration of tretinoin was influenced by vehicle and concentration of this drug used in formulation.

A tretinoína é usada no tratamento de acne e é considerada como padrão de ouro para o tratamento do fotoenvelhecimento. Em altas concentrações, é relatada como um agente para peeling químico superficial, com poucas considerações sobre a penetração na pele. O objetivo deste estudo foi avaliar a influência da concentração do fármaco e os veículos comumente usados na penetração cutânea da tretinoína. Testes in vitro de penetração foram realizados com células de difusão de Franz equipados com pele da orelha de porco e 10% de solução aquosa de metanol no compartimento receptor. As formulações estudadas, creme ou dispersão hidroalcoólica, contendo 0,25%, 1% e 5% de tretinoína foram colocadas no compartimento doador, durante seis horas. A concentração da tretinoína foi medida por cromatografia líquida de alta eficiência. A maior quantidade de tretinoína foi detectada no estrato córneo com diferenças significativas entre as três concentrações. A dispersão hidroalcoólica foi o melhor veículo. Quantidades significativas de tretinoína foram encontradas nas camadas profundas da epiderme. A formulação com 0,25% de tretinoína mostrou melhores resultados em termos de porcentagem penetrada na pele. Por fim, a penetração de tretinoína na pele foi influenciada pelo veículo e pela concentração desta utilizada na formulação.

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RESUMEN

Chemically stable ester derivatives of vitamins A, C and E have become a focus of interest for their role in the satisfactory results in skin aging treatments. Accordingly, the aim of this study was to evaluate the physical and chemical stability of a cosmetic formulation containing 1% retinyl palmitate, ascorbyl tetraisopalmitate and tocopheryl acetate, alone or in combination. In the studies of physical stability, a Brookfield rheometer was used to determine rheological behavior of formulations containing the vitamins. Chemical stability was determined by HPLC on a Shimadzu system with UV detection. Results showed that formulations had pseudoplastic behavior and that vitamins did not alter their apparent viscosity and thixotropy. In the chemical stability studies, first-order reaction equations were used for determinations of the shelf-life of vitamins derivatives considering a remaining concentration of 85%. Combined vitamins in a single formulation had a slightly lower degradation rate as compared to different preparations containing only one of the vitamins. Considering that many cosmetic formulations contain vitamin combinations it is suggested that the present study may contribute to the development of more stable formulations containing liposoluble vitamins.

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