A few days ago, I implored the Hivemind for assistance re: my very itchy chihuahua, who was suffering from a very bad round of seasonal dermatitis. A few experiments and calls to the vet later and we have success!
First, I washed him with a tar oil soap. This is the same thing as Neutrogena T-Gel - the stuff for super gnarly dandruff and eczema and psoriasis. I just bought the CVS version, nothing special. He was thoroughly massaged with it, had to stand around pitifully to let it work for a few minutes, and then suffer the indignity of being rinsed off in the kitchen sink. It's rough being 3 lbs.
Then, I rubbed a little benadryl gel on the places he's gnawed bald and into other areas where he's started to itch. He also was tricked into taking his oral dose of 5mg of Zyrtec.
I'm happy to report that Cooper is now itchy free! We're looking forward to when his hair starts growing back, because he looks like a diseased sewer rat currently. The vet said we'll likely have to re-wash him with that shampoo every few days and apply the benadryl gel a few times daily until the itchy fully passes.
VICTORY IS MINE! Or...OURS! Thanks, GT!
Happily gnawing a rawhide instead of his own ass.