Drug Permeation Through the Skin and Topical Preparations

Drug Permeation Through the Skin and Topical Preparations 

The intact epidermis behaves qualitatively as do cellular membranes in general (Scheuplein Blank, 1971). Topically applied chemical substances diffuse through the functional barrier provided by the epidermis at rates determined largely by their lipid/water partition coefficients but more slowly than through cellular barriers elsewhere in the body (Scheuplein, 1965). Percutaneous absorption in vivo is a summation of ten steps that have been enumerated by Wester Maibach (1983). 

The average thickness of the stratum comeum in laboratory and domestic 

The state of hydration of the stratum comeum, which is normally maintained at 10-15%, affects the rate of penetration of chemical substances. By increasing the state of hydration to 50%, the rate of permeation of some chemical substances through the epidermis can be increased up to tenfold (Idson, 1983). Occlusion has been shown to enhance the pharmacological effect of topically applied hydrocortisone and fluocinolone acetonide (McKenzie, 1962), but percutaneous absorption of drugs is not necessarily increased. The degree of occlusion-induced absorption enhancement appears to increase with increasing lipophilicity of drug substances. 

Formulations containing an absorption promoting substance, such as propylene glycol or sodium lauryl sulphate, may increase the permeability of the stratum comeum to water-soluble drugs. Propylene glycol is a commonly used vehicle in topical corticosteroid preparations for veterinary use. Various aprotic solvents, which include dimethylacetamide, dimethylformamide, dimethylsulphoxide, tetrahydrofurfuryl alcohol, and 2-pyrrolidone, serve as penetration enhancers of polar drugs (Barry, 1983). Dimethylsulphoxide 

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