I have dealt with many a blister in my time. When I get one, I stick a disinfected pin through it and drain the liquid, leaving the skin which protects the tender underlayer. In time, the skin will peal off on it's own but by then the underlayer has had time to toughen up. In your case, with the skin having already come off, I would suggest an antibiotic creme and a bandage when you have to wear shoes. Let it have open air when you don't have to wear shoes. That raw area will toughen up in no time when exposed to the open air, you just don't want to get it dirty. I don't think I would put Prid on it due to the chemicals in it. Maybe Vasoline but not Prid.