Are you feeding dry or canned? I was looking at the ingredients list of both and I would stay away from feeding Hill's Prespription Diet. If you look at the ingredients list of the dry food, these are the first few ingredients:
Brewers Rice, Corn Gluten Meal, Pork Fat (preserved with mixed tocopherols and citric acid), Chicken By-Product Meal, Dried Egg Product, Dried Chicken, Powdered Cellulose, Fish Meal, Chicken Liver Flavor, Calcium Carbonate, Dried Beet Pulp
Ingredients are always listed in descending order, generally the first 3 ingredients make up 75 % of the total in this case, the first ingredient is a carbohydrate. Cats are obligate carnivores don't only not require a large amount of carbs, they in fact shouldn't eat a lot of carbs. Whereas with kidney problems the amount of protein should be reduced it is much more important to use an easier digestible form of protein and avoid food preservatives, coloring agents, insecticides, buildup of sodium and phosphorus.
Brewer's rice is an inexpensive form of carbohydrate, and does not contain the full nutritional benefits of whole grain brown rice. Since this is a carbohydrate this ingredient should be listed way down on any cat food label. Caution also should be used for cats with food allergies as rice is a known allergen.
Corn gluten meal whereas a cheap and incomplete vegetable protein is also a cheap filler. Many cats are allergic to corn aside from the fact that at least 1/3 of the corn supply in this country is genetically modified, not to mention what we get from other countries.
Cats need a higher fat diet than dogs but pork fat of all things isn't exactly high quality.
Dried beet pulp is a by-product of sugar production from sugar beets. It's another cheap filler and questionable at best.
If at all possible cats should not eat a dry food diet, raw food or canned is much better. Dr. Lisa Pierson, DVM, states, "It is troubling to think about the role that chronic dehydration plays in feline kidney failure. And remember, cats are chronically dehydrated when they are on a diet of predominantly dry food".
The company's canned food doesn't fare much better though
Water, Pork Liver, Chicken, Pork By-Products, Brewers Rice, Oat Fiber, Corn Starch, Glucose, Chicken Fat (preserved with mixed tocopherols and citric acid)
Pork is high in uric acid and hard to digest, not a meat that is recommended. Water is the first ingredient, then pork liver basically as the main ingredient, whereas liver contains valuable vitamins it also contains many toxins and is not recommended to feed as the main ingredient on a daily basis.
Brewer's yeast (see above)
Glucose, why on Earth would any cat but especially a cat with kidney problems need added sugar in their diet?
Hills/Science Diet is notorious to preserve with BHA, BHT, propylene glycol and ethoxyquin, neither of which needs to be disclosed but are known carcinogenics.
I'd probably go with a canned diet if raw is not an option for you. Nature's Variety and Wysong Archetype/Gourmet are the ones that I would opt for but there certainly are others, just check the label.
HTH