Any suggestions on what to feed a cat that has CRF?

My beautiful Peanut is 20 yrs. old and very sick. His thyroid level was diagnosed at 18 very high, it since has been treated successfully with the Methimazole gel. He recently stopped eating and drinking again, but this time it is not his thyroid it is his kidney's. The vet said that it is a side effect of his thyroid. He hydrated him a couple of days ago, but he still will not eat or drink. I guess I am trying to avoid the inevitable, by giving him a little food and water with an appetite stimulant in a syringe, orally, hoping he will begin to eat. Any idea's would be appreciated.