This is more than the early stages of kidney disease. Your cat should be on subcutaneous fluids on a daily basis; ask your vet to show you how to do this at home. Give your cat some pureed raw beef kidney at each meal. A good chinese herbal combination to use is called Rehmannia Eight. Also give cod liver oil, CoQ10, a good probiotic, chitosan and calcium carbonate. The amounts will depend on the cat's weight and what it will tolerate. But it will definitely need daily fluids, for a while at least.