Penetration and permeation into human skin of fusidic acid in different galenical formulation.

The penetration into the horny layer and permeation through the skin of fusidic acid, incorporated in different bases, e.g., cream, ointment and a gel (Fucidine), was investigated in vitro in a penetration chamber, using human skin. Whereas the horny layer offers a marked barrier to penetration in normal skin, this barrier can be greatly reduced by damaging the horny layer by adhesive tape stripping. Fusidic acid showed penetration into the different layers of skin which was related to the duration of application, including the penetration chamber fluid, i.e., there was penetration of the entire skin thickness. In the presence of spontaneous changes in the horny layer, as in seborrhoeic warts and similar conditions, fusidic acid penetrated well into the deeper layers of the skin. Fusidic acid is thus a substance which permeates better in regions where the horny layer is damaged, and where it can attain high levels, which in practice are antimicrobial. Penetration into the skin is thus a function of damage to the horny layer and the quality of the horny layer itself. From this point of view the amount of absorption in dermatoses depends on the area of skin with damage to the horny layer. Penetration through normal skin can be disregarded.