I'm only recently dealing with renal failure in my 13+ year old dog, but I'm assuming you're having the same nausea, vomiting and inappetance issues. I'm having much better luck getting my dog to eat using homemade food. I've also found the item of most importance is getting her to eat anything at all - even if it isn't the best for her kidneys. I'm sure your vet explained that you need to get phosphorus out of your dog's system. Calcium (Tums) binds with phosphorus and clears it out of the body. If calcium is high, you can use aluminum hydroxide, which is another antacid. Most aluminum antacids are liquids and contain other things your dog shouldn't have, but I found Alu-tab on the internet. Alternagel tabs are another option.
Two very expensive supplements recommended by our vet didn't seem to do much, so we have discontinued their use. They are Azodyl and Epakitin powder that goes in food. The Epakitin obviously won't do you any good if the dog won't eat. :-) In reading the ingredients for both, I found I can provide the same benefit, if not better, with:
One Tums twice a day
A Senior vitamin (the only one I found without phosphorus was Nutri-Vet Senior Vitality
Probiotics and digestive enzymes like acidopholus
Our dog is also low in potassium, so we will continue using those supplements from the vet. Potassium is very important to heart function.
Pepcid or Zantac is great for helping with high acid levels in renal failure patients, but it also tends to cause loss of appetite when used daily. We had to really slow down on that and only give it at night so as not to make her appetite even worse.
Back to my statement that it's better to get your dog to eat anything at all even if it isn't the best for the kidneys - I've had some really good results with offering a great variety of foods in small amounts throughout the day. Chica is noticeably improved over the past couple of weeks, and has already gained back about half of the 15 pounds she lost before diagnosis. I use rice cooked with low-sodium Swanson's chicken broth and a little butter (not margarine) as a base. Use the higher-fat, cheapest ground beef, pork or lamb as a more easily digestible protein source to mix in with the rice. When cooking the meats, make sure they are cooked very lightly - cooking to well-done increases phosphorus. Canadian bacon is another low-phosphorus choice, along with hard boiled eggs. The egg whites are the best, and the yolks are high in phosphorus, so go with about 1/4 of the yolk. Boiled, dark meat chicken or turkey is another great source of lower phosphorus protein.
The tricky part of the kidney diet is meeting your dog's nutritional needs. That why the vitamin supplement is so important.
What is your vet using to treat the nausea and vomiting? If you're using reglan (metoclopromadine), you might ask for something else. Reglan is metabolized in the kidneys, and my dog ended up with a toxic dose because she couldn't process it. Her symptoms were extreme restlessness, couldn't lay still for more than 5 minutes, whining and crying, very fast pulse and respirations, and finally trembling that worsened to all-out shaking. The sad thing is that the reglan greatly helped the nausea and appetite issues. For now, Chica is doing well on 1/4 to 1/2 of the prescribed dose. I'm sure as time goes on and the kidney damage worsens, we'll have to try another medication - all of which are far more expensive. One vet recommended Dramamine (for motion sickness) but it didn't seem to have any effect. You might see if it helps your dog though since it's processed in the liver instead of the kidneys.
I found out rather quickly there really isn't much we can do for kidney disease in our dogs. Once the damage is done, it's permanent, so all treatment is palliative to help the remaining good tissue do its job for as long as possible, and keep the dog as comfortable as possible. Much of what I found out regarding diet issues I learned at this web site: http://www.dogaware.com/kidney.html
Print out the 40-page article and take the time to read it. Had I not read through it, I'm convinced Chica would be about done in by now. There are lots of ideas for various foods and they are listed with phosphorus content. Also tips on how to "pill" your dog. I can't trick Chica with the old pill-in-a-piece-of-cheese routine any more, so I've become the fasted dog-piller in the West these days. LOL! She doesn't mind it at all and at least I'm certain she got her meds and didn't spit them out.
Hopefully, you can try some of these ideas and get somewhere with getting food in your dog before having to resort to the feeding tube. Like you, I don't know that I could put my old dog through something like that. Matter of fact, Chica is such a Type-A dog I'm positive she wouldn't put up with it. I've found that once the nausea was under control, Chica kept herself hydrated on her own just fine. I know she'll never be her old hyperactive self again, but she's back to playing with our other dog and taking short walks again. Overall, I'm happy that she's still hanging in there and enjoying what life she has left.