I have always purchased my Levimasole HCL and Flubendazole 10% from Charles Harrison at http://www.inkmkr.com/Fish/
There are some very helpful articles and dosing information on the site.
I would not go near that 52 gm for $20 stuff at that link. I do not know what other stuff is in it. This is what the label says"
From http://www.jefferslivestock.com/images/label/16398.htm
What the heck is "activity" What else is in there?
I've used the 52gm for $20 "Prohibit" brand with perfect success, no harmful side effects, and no post worm infections.
This link includes the MSDS & Label for the actual product, from the manufacturer:
http://agrilabs.com/Products.aspx?CategoryUid=10&ProductUid=109
I believe "activity" refers to the fact that Levamisole HCL depends on a chemical reaction to do it's job as a dewormer. If you were to use inactive Levamisole, that reaction would not take place. According to it's label, once mixed to form the solution, it only has a shelf life of 3 months.