Shed snake skin and hairless mouse skin as model membranes for human skin during permeation studies

Percutaneous permeation of basic compounds through shed snake skin as a model membrane

Relationships between the in-vitro permeability of basic compounds through shed snake skin as a suitable model membrane for human stratum corneum and their physiochemical properties were investigated. Compounds with low pKa values were selected to compare the permeabilities of non-ionized forms of the compounds. Steady-state penetration was achieved immediately without a lag time for all compounds. Flux rate and permeability coefficient were calculated from the steady-state penetration data and relationships between these parameters and the physicochemical properties were investigated. The results showed that permeability may be controlled by the lipophilicity and the molecular size of the compounds. Equations were developed to predict the permeability from the molecular weights and the partition coefficients of basic compounds.

Dodecyl N,N-dimethylamino acetate and azone enhance drug penetration across human, snake, and rabbit skin

The effectiveness of the penetration enhancers, dodecyl N,N-dimethylamino acetate (DDAA) and Azone, on pretreated human epidermis for the permeation of model drugs, indomethacin, 5-fluorouracil, and propranolol-HCl, was studied in in vitro diffusion cells. Snakeskin (Elaphe obsoleta) and rabbit pinna skin were compared as possible models for human skin. The drug concentrations were analyzed by HPLC. With all skins and all model drugs, DDAA increased drug permeability at least as well as Azone, and in most cases it was a more effective permeation enhancer. The relative permeation improvements in human skin, snakeskin, and rabbit skin were 10- to 20-, 5- to 50-, and 20- to 120-fold, respectively. Tritiated water served as an indicator of skin condition. Its penetration in the skin samples was independent of the drugs used, and both penetration enhancers significantly increased the flux of tritiated water through all skins. Thus, DDAA and Azone significantly increased the permeation of lipophilic and hydrophilic model compounds. Rabbit pinna skin was a poor model for human skin in vitro, while snakeskin was much closer to human skin in terms of transdermal permeability. In most cases drug permeability decreased in the order rabbit much greater than human greater than or less than snake.