Transdermal drug delivery stratum corneum

Wertz, P.W., and D.T. Downing. 1989. Stratum corneum Biological and biochemical considerations. In Transdermal drug delivery Developmental issues and research initiatives, eds. J. Hadgraft, and R.H. Guy, 1. New York Marcel Dekker... 

M. L. Francoeur, G. M. Golden, and R. O. Potts, Oleic acid its effects on stratum corneum in relation to transdermal drug delivery, Pharm. Res. 7 621-626 (1990). 

The upper layers of epidermis, the stratum corneum, is a principal barrier to transdermal drug delivery. It consists of a heterogeneous structure made up of keratinized cells and lipids. 

A new generation of transdermal drug delivery (TDD) system was developed to contain one or more skin permeation enhancers in the surface adhesive coating layers. This TDD system has been found, experimentally, to release the enhancers to the surface of stratum corneum to modify the skin s barrier properties, prior to the controlled delivery of the active drug. The extent of enhancement in skin permeability appears to be dependent upon the chemical structure of drug to be delivered transdermally as well as the type and the concentration of enhancer used. The mechanism of skin permeation enhancement have been explored and are analyzed in this report. 

This new type of transdermal drug delivery system is capable of releasing one or a combination of two or more skin permeation enhancers to the stratum corneum surface in order to modify the skin s barrier properties (10), prior to the controlled delivery... 

Turner, N.G. Nonato, L.B. Visualization of stratum corneum and transdermal permeation pathways. In Mechanisms of Transdermal Drug Delivery Potts, R.O., Guy, R.H., Eds. Marcel Dekker, Inc. New York, 1997 83,14-0. 

Wertz PW and Downing DT. Stratum Corneum Biological and Biochemical Considerations. In HadgraftJ and Guy RH (eds.). Transdermal Drug Delivery Developmental Issues and Research Initiatives. Marcel Dekker, Inc., New York 1989 ... 

Because of the very extensive barrier properties of the stratum corneum, it is often necessary to increase the intrinsic rate of dermal or transdermal drug delivery to achieve the required therapeutic drug levels. In these instances, skin penetration and permeation enhancement... 

Abraham, W., Kitson, N., Bloom, M., and Thewalt, J.L. (1997). Investigation of membrane structure and dynamics by deuterium NMR application to stratum corneum, in R.O. Potts and RH. Guy (eds.). Mechanisms of Transdermal Drug Delivery, New York Dekker, pp. 163-198. 

Liquid crystalline phases also seem to play an important role in topical and transdermal drug delivery. As discussed above, the protective properties of the stratum corneum seems to depend on the properties of its lipid fraction. More specifically, these have been found to form lamellar structures (169, 170), which could be expected to reduce the transdermal penetration of drugs, as well as water evaporation. On the other hand, the presence of Azone may induce reversed-type phases (172). Thus, the generation of oil and water channels seems to correlate with the commonly observed enhanced transdermal penetration of drugs caused by this penetration enhancer (186). 

Transdermal drug delivery through iontophoresis has received widespread attention. A long-term delivery with transdermal DC voltage of <5 V was used (Phquett and Weaver, 1996). High-voltage pulses up to 200 V decaying in about 1 ms have also been used on human skin for enhancement of transport by electroporation (Phquett and Weaver, 1996). The effect was found to be due to the creation of aqueous pathways in the stratum corneum. 

To date, Raman spectroscopy has been used for the characterization of stratum corneum, epidermal membrane and dermal tissue. Of current interest is the administration of therapeutic agents across the skin barrier (transdermal drug delivery) however, there are a number of difficulties which involve the supply, storage and use of biohazardous human material. 

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