I believe that the lotions also have Magnesium sulfate in them.

The difference is that the Kirkman cream has the concentration listed on the label, and provides a little measuring tool.

The lotions do not give the concentration in them.

However, we don't know how much IS absorbed, only that some is.

The plus side of the topicals is that they don't cause loose stools, which some people do get with oral products.

I posted this article recently, I found on the net concerning epsom salts and absorption potential thru the skin:
http://neurotalk.psychcentral.com/post864114-32.html

I know from my reactions to the lotion, I absorb nicely. I apply about a nickel sized dollop of my lotion on each arm and rub it in on the undersides of my forearm where the skin is thin and sensitive. I also do the wrists well, as blood vessels are near the surface there. (and I can have hand issues too)
I always sleep deeply when I do this. When I don't I notice it right away. Also applied to my left foot when it swells, the swelling goes down by the next morning and stays down for a couple of days. It is really helping with this problem that hurts me.