I'm sorry to hear of this with your CKC. Can you tell me, please, which medication was in that tablet? I suspect that is was a steroid such as prednisone which usually addresses skin allergies well but if a secondary bacterial or yeast infection has arisen, your dog's itching will return as soon as the prednisone wears off. Can you upload a photo of representative skin to our conversation? You can use the paperclip icon in the toolbar above your message box (if that icon is visible) or you can use an external app such as imgur.com or dropbox.com. I can be more accurate for you if I can see what you're seeing. I'm going to post my synopsis of the itchy dog for you. Please peruse it and then return to our conversation with additional information, questions and concerns if you wish.
Pruritic (itchy) dogs are suffering from an allergic dermatitis in the great majority of cases. Allergies to flea saliva, environmental allergens (atopic dermatitis) such as pollens, molds, dust and dust mites, and foods should be considered. (Paw and extremity licking indicates both atopy and a food intolerance and so it behooves vets to distinguish one from another.) In many instances, a concomitant pyoderma (bacterial skin infection), yeast infection (Malassezia), or mange mite (Demodex or Sarcoptes) might be contributory.
Your dog's vet can check a sample of your dog's skin surface microscopically (a “cytology”) for abnormal numbers of bacteria and yeast and skin scrapings can be taken in an attempt to find mites. Pyoderma is treated with a minimum of 3-4 weeks of an antibiotic in the cephalosporin class such as cephalexin (Keflex) and yeast is addressed with ketoconazole for at least a month.
Our dermatologists tell us to apply an effective over the counter flea spot-on such as Advantage, a fipronil-containing product such as Frontline or one of the newer prescription products available from your dog's vet even if fleas aren’t seen. Dogs can be such effective groomers so as to eliminate all evidence of flea infestation. Dogs who remain primarily indoors can contract fleas because we walk them in on us and flea eggs and larva can remain viable in your home for months. As the weather warms or you turn on heaters at this time of year, egg hatches are common. In severe cases, an anti-allergenic prescription glucocorticoid such as prednisone will work wonders for dogs allergic to the saliva of the flea. If you have other pets they may have fleas too but may not be allergic to the flea’s saliva. I'm pleased to hear that fleas no longer appear to be a problem.
Environmental allergies are usually initially addressed with prednisone as well. In some dogs an over the counter antihistamine such as clemastine (Tavist) at a dose of 0.025 - 0.75mg/lb twice daily or diphenhydramine (Benadryl) dosed at 1-2mg/lb twice daily may be effective. Antihistamines, however, aren’t reliably effective. Adding fish oil to the diet at a dose of 20mg/lb daily of the EPA in the fish oil might synergize with antihistamines to provide better anti-pruritic action. The omega-3 fatty acids in fish oil are antiinflammatory but may take 8-12 weeks to kick in. The new cytokine antagonist oclacitinib (Apoquel) is likely to revolutionize how we address atopic dogs and should be discussed with your dog's vet. Oclacitinib works as well as a steroid without a steroid's adverse effects.
Food intolerance/allergy is addressed with prescription hypoallergenic diets. These special foods contain just one novel (rabbit, duck, e.g.) animal protein or proteins that have been chemically altered (hydrolyzed) to the point that your dog's immune system doesn't "see" anything to be allergic to. The over the counter hypoallergenic foods too often contain proteins not listed on the label - soy is a common one - and these proteins would confound our evaluation of the efficacy of the hypoallergenic diet. The prescription foods are available from his vet. There are many novel protein foods and a prototypical hydrolyzed protein food is Hill’s Prescription Diet z/d ultra. (I prefer the hydrolyzed protein diets.) A positive response is usually seen within a few weeks if we’ve eliminated the offending food allergen. Food intolerance can arise at any age and even after our patient has been eating the same food for quite some time.
We need to consider seborrhea in such a patient as well. This is skin disorder of keratinization and maturation. It's a diagnosis of exclusion of the above mentioned skin disorders and can be suggested by skin biopsy. I understand your frustration but a thorough and methodical approach to such a dog should be very helpful. If your vet isn't wiling to properly "work up " your CKC, please consider having a specialist veterinary dermatologist (please see here: www.acvd.org) take a look at him.