Development of a Polymeric Patch Impregnated with Naproxen as a Model of Transdermal Sustained Release System

This paper describes the preparation and characterization of transdermal patches impregnated with naproxen. A mixture of ethylene vinyl acetate and Eudragit® E100 (80:20, w/w) is used as a polymeric matrix to obtain a thin membrane to be impregnated. Drug impregnation is carried out under pressurized CO2 as a processing medium according to a two-step procedure. The patch is first soaked at 1000 psi and 22°C for 2 h, and then foamed as a result of the rapid release of CO2 pressure in order to increase the porosity of the surface. Subsequently, the naproxen solution is placed in contact with the membrane and then soaked in CO2 at 450 psi and 37°C for 2.5 h to enhance the mass transfer of drug into the polymer matrix. The characterization of the resulting samples by liquid chromatography, microscopy, and calorimetry provides information on naproxen content and distribution. Patches synthesized in this way are loaded with about 1% naproxen. The drug release and diffusion process through a membrane have been studied chromatographically using a Franz diffusion cell. Results have shown that a sustained delivery for more than 24 h is obtained.