I know at least one of the vet-quality flea products does treat sarcoptic mange.....might be K9 Advantix. It would be best to ask your vet which product might work for this purpose, you'd have to buy it from him anyway.

 

If it were sarcoptic mange, she would be EXTREMELY itchy. The movement of sarcoptic mites on the skin drives dogs nuts...she would be going crazy. If your vet did a scraping and didn't see any mites (be it demodex or sarcoptes) then it's a pretty safe bet it isn't mites. Pertaining to your question, Interceptor, Sentinel, and Revolution all prevent sarcoptic mange.

Then what's causing the dry skin? It could be a few things...one of which is ALLERGIES. Dogs get very itchy from allergies in the places you described as having dry skin, and they can actually cause an infection in that area, possibilities being a bacterial or yeast infection. In my experience as a tech, wrinkly dogs (pugs, bulldogs, shar peis, etc) are especially prone to these type infections because cleaning the wrinkles (esp on their booties) is often neglected or forgotten and infection is harbored there.

What to do? Medicated shampoos, like your vet gave you, are great. Malaseb shampoo treats yeast infections and is a great product. Actually, look for a shampoo called "universal medicated" and use it in conjuntion with whatever other medicated shampoo your vet gave you. A product called Gentaved spray also works wonders on those types of areas.

If the infection persists or gets worse, or if the skin starts turning a dark color and looking like "elephant skin" bring her back to the vet, because she'll probably need a course of antibiotics.

Whew, long post! I hope that helps somewhat!