I'm not sure about the shampoo, I just use an oatmeal based one, whichever I can find at the time, anything but Hartz... I've heard bad things about it and I can't remember if it was on this forum or not.
As far as "medicine" I give my sibe Brewers Yeast tablets, it helped his coat become shiny and grow in better than before, it's not as drabby of a color as it used to be. And he loves them, apparently they taste good, even though they smell awful lol