The release and percutaneous permeation of anthralin products, using clinically involved and uninvolved psoriatic skin

Abstract

The release and permeation of 1% Westragel and 1% Westrastick and three commercial 1% anthralin products were investigated in vitro with the use of a Franz diffusion cell unit. An inert Teflon membrane with a mesh opening of 74 mu was used for measuring the rate of release. Involved psoriatic and uninvolved human skin collected from the same subjects were used for the permeation study. The permeation of danthron and dianthrone, the major degradation products of anthralin, was also studied with the use of microemulsion gels of 1% danthron and 1% dianthrone, which were prepared in the same way as 1% Westragel. The penetrating anthralin, danthron, and dianthrone were stabilized by a modified receptor fluid, and sample solutions were analyzed by a high-power liquid chromatography method. Involved psoriatic skin was found to be much more permeable to anthralin than was uninvolved psoriatic skin. The slow permeation rate of anthralin, danthron, and dianthrone through normal skin and uninvolved skin indicates that the stratum corneum is the rate-limiting barrier. In involved psoriatic skin, the release rate of anthralin from the topical product becomes the rate-determining step. Large individual variations were found in the permeation of anthralin through involved psoriatic skin, suggesting that the permeation rate of anthralin also may depend on the disease state of psoriatic patients. The anthralin molecule, possessing both hydrophilic and lipophilic centers, diffused significantly faster than did danthron and dianthrone. Westragel, 1%, showed the highest diffusion rate as well as the highest driving force when compared to other commercial 1% anthralin products. This suggests that 1% Westragel may be an optimal design, especially for short-contact anthralin therapy.