its very simple, just get some redmond's clay or some Bentonite clay. you can just smear a fair amount on and let it dry, then shower it off. or you can make a poultice with it. put a fair amount of the clay in a small towel, place the clay directly on top of the spot, place the towel over the clay, then wrap gauze or something around it so it stays on there. you can leave that on for an hour or two. do it at home while watching a movie or something.
the clay does two things. the first is to draw out the poison, the second is to nuetralize it.