i found this:

http://scienceblogs.com/retrospectac...roved_by_t.php
I've always been interested in how these skin patches work, specifically what they contain that transfers the enclosed drugs into the skin. After a quick search I found that one common ingredient in many transdermal patches is the chemical DMSO (if you are in a lab, you may have heard of it). DMSO (dimethyl sulfoxide) is a solvent and a by-product of the wood industry. In 1961 a Dr. Jacob noted that the chemical was able to penetrate the skin deeply without causing any damage. Later it was observed to be a superior solvent for pharmaceuticals, and capable of transporting chemicals across and into skin (for better or worse). Obviously you'd want to be careful with DMSO (for example, LSD is sometimes dissolved in DMSO), but these properties made it quite useful for introducing therapeutic drugs into the skin via the patch. The release of drug was constant and predictable, and patches were difficult to abuse (the strong painkiller fentanyl is sometimes delivered this way.)

and:

http://www.madsci.org/posts/archives...0244.Bc.r.html

There is a lot of research on this and other novel routes of drug delivery, by practically every major research drug company. Some chemicals can enhance delivery of drugs across the skin. One example is dimethyl sulfoxide (DMSO). It is (unfortunately) sold over the counter. It helps drugs gain entry basically by damaging the cell membrane to make it more permeable to other substances. This is generally not a very good idea. Not only does it damage the skin and other cells, sometimes permanently, but it also makes it difficult to control the amount of drug or other agent that passes through the membrane

hope this helps.