In vitro drug release from liquid crystalline creams; cream structure dependence

Abstract

The general aim of this study is to develop skin-compliant liquid crystalline creams for controlled transdermal drug delivery. To achieve this aim, we try to use the colloidal gel structures inside the creams to control the drug release rate. This study deals specifically with the relationship between cream structures and drug release in vitro. Creams have been prepared by mixing Brij96^R (polyoxyethylene(10)-oleylether, a nonionic surfactant) and water. Depending on the mixing ratio, they can adopt a lamellar, a viscous isotropic, or a hexagonal gel structure. The model drug benzocaine (ethyl p-aminobenzoate) was solubilized (1%) in the creams without disturbing the gel structures. Because the creams are able to swell quickly upon contact with water, an in vitro drug release model was developed using a water-impermeable membrane (dialysis membrane impregnated with silicone adhesive) to separate the cream from the aqueous acceptor phase (0.1 M HCl). In the lamellar and hexagonal creams the effective diffusion coefficient of benzocaine increases gradually with the water content due to a volume increase of the hydrophilic domains of the creams that form the continuous phase. In the viscous isotropic cream the diffusion of benzocaine is relatively high, most likely because of the low tortuosity of the cream.