Occlusive properties of monolayer patches:: In vitro and in vivo evaluation

Purpose. Patches can cause a different grade of skin occlusion, depending on matrix composition and thickness, backing layer material. The aim of this work was to verify if in vitro water vapour permeability (WVP) values are predictive of transepidermal water loss (TEWL) and Fourier-transform infrared (FTIR) spectroscopy values measured in vivo after 24 h of methacrylic or acrylic monolayer patches application. The correlation between both in vivo methods has been evaluated. Methods. The WVP, TEWL and FTIR measurements were performed by using four patches made of a methacrylic or an acrylic polymeric system (250 and 500 mum thickness on a polyurethane backing layer). A fifth patch was made of the methacrylic matrix on a polyvinyl chloride backing layer. Results. A good correlation was found between TEWL values and IR water/lipid absorbance ratios. The in vitro WVP values are in a good correlation with the results of both in vivo methods: TEWL = -0.01WVP + 21.31 (R-2 = 0.9312); FTIR water/lipid ratio = -0.01WVP + 27.15 (R-2 = 0.9447). Conclusions. The in vitro method proposed for measuring the WVP is predictive of the degree of occlusion resulting from the in vivo application of monolayer patches.