Determination of in vitro usnic acid delivery into porcine skin using a HPLC method.

Usnic acid, a lichen metabolite, has been proposed as a potential topical treatment for microbial skin lesions, burn wounds as well as a sunscreen. An isocratic HPLC method was validated according to FDA's Guidance for Industry: Bioanalytical Method Validation to determine skin penetration and permeation of usnic acid. The penetration and permeation of usnic acid was evaluated using Franz cells and porcine skin. The method was valid according to selectivity, linearity, precision, accuracy and stability. Usnic acid was quantified in the skin surface (6.13 µg cm(2)), stratum corneum (34.4 µg cm(2)), viable epidermis (5.6 µg cm(2)), dermis (28.2 µg cm(2)) and receptor compartment (3.2 µg cm(2)). These results help us to understand the penetration profile of usnic acid and plan topical therapeutic approaches as well as new topical delivery systems to modulate this penetration profile.