Hello, I am Dr. Zoe, a licensed veterinarian here to help. It sounds like we have two issues here: 1)Skin issue and 2)Vomit/hacking. How long has the hacking been going on? Is this new or a long-term issue?

She has episodic vomit fits...this could be related to allergies especially if this seems to coincide with when her skin flares up. Perhaps her throat/nose gets inflamed as well. This is not common. If she was mine I would do a trial with anti-nausea medication. Have you done this before? I would at least put her on Pepcid AC 10mg every 12 hours which you can get OTC or another similar drug like Zantac.

And then the skin. My top recommendation is to treat the active skin infection whether this be bacterial or yeast to get her some relief. And then have a discussion with your vet about underlying allergies, which hopefully you already have. The top two underlying allergies in dogs to cause these skin signs is food allergy and atopic dermatitis (environmental allergy). Usually we start by doing a 2 month food trial with a hypoallergenic diet which has a novel protein she has never seen (like duck, venison or fish). If this has been done, then the next step is to explore atopic dermatitis with allergy testing (serum or intradermal) and you can request a referral to see a dermatologist for this or your vet should provide serum allergy testing. The results can be fascinating. But once you confirm her atopic dermatitis with this you can elect to do either allergy shots or start her on Atopica (cyclosporine). Have you already been through this discussion? IF so, let me know where you are in the process. Some people elect to forgo the serum allergy testing in lieu of treating with daily Atopica (but it is expensive in a large dog).

Oh, to treat the bacterial or yeast infection will require an oral antibiotic and oral antifungal. Your vet should confirm which infection is present based on a skin scraping (not just for mites). And by treating this infection it will dramatically cut down on the chomping/biting! The prednisone is probably the absolute most effective drug we have for stopping chewing. Perhaps, you need to discuss using a higher dose, or trying a differnt form like methylprednisolone. But I always adivse people this will not work by itself if we are not treating the underlying infection (and a topical is not going to treat this).

Okay, and I almost forgot to say you absolute cannot give rimadyl and pred together. That is contraindicated!! This will cause a stomach ulcer. YOu must do one or the other. Call your vet ASAP to discuss this!!