Blue, as mentioned above have you tried Benadryl? It's 25mg per 50 pounds for dogs.
Also, if you want a more natural solution to your dogs allergies, you might want to look at Serrapeptase. It's great for all sorts of things, especially allergies. You can get it where it's a powder in pill form and put it in your dogs water (it's odorless and tasteless) or give him the entire thing. Just thought you'd like to know about another more natural option.