PDS is just the name brand of a proprietary concoction of alpha hydroxy acids (it stands for "Problem Dry Skin"--but it was made with ichthyosis specifically in mind). It's available OTC, no prescription needed. It's made by a company called NeoStrata. They have their own webpage with info about it: http://www.neostrata.com/casestudies-pds.html
As far as I know, the only way to purchase PDS is to purchase directly from NeoStrata.
Hope that helps,
[This message has been edited by Laura Phillips (edited March 15, 2001).]