Demodectic mange is being discussed at present on one of my dog groups, and the treatment being mentioned is Ivermectin, but this needs to be used with great caution in some breeds particularly Collies and other related herding breeds, although problems have been found in totally unrelated breeds.
This is what I found about an americam treatment:
The main drug used to treat generalized demodex is called Mitaban. Unfortunately, Upjohn no longer makes it, so we have to use substitutes. Mitaban has to be used precisely by label instructions. Since it is difficult for people to do this properly in their homes, we treat most pets in our hospital. Pets are dipped once per week, in between these dips your pet should not be bathed. We continue dipping until successive skin scrapings are negative for the mites.
If Mitaban does not work there are other medications that are used with varying success to cure the problem. These include oral Ivermectin and Milbemycin (Interceptor). Side effects like excess salivation, incoordination, even coma and death are possible, so they must be used judisciously. They should not be given to Collies, Shelties, australian shepherds, or dogs that are positive for heartworm. There can be no guarantee that they will work, especially in a disease that is so closely associated with the immune system. Spaying infected females is helpful.