Vet at FirstVet answers:
Dogs with kidney failure urinate a lot and are very thirsty. Inappetence is common later on in the disease because the kidneys are unable to rid the body of toxins, making the dog feel sick. Loss of muscle mass occurs due to the poor appetite and the kidneys leaking protein. Eventually, the dog becomes anaemic because the kidneys fail to produce the hormone EPO, which stimulates red blood cell production, making the dog feel very tired.
Aside from a special diet, there are some things you can do to help your dog. For example, anti-nausea medication can be used when the appetite worsens. Treatment against high blood pressure is often also required. It is a good idea to regularly check the electrolyte levels (including Sodium, Potassium, Phosphate and Calcium) and protein levels in the blood. It is impossible to say exactly how the disease will progress specifically for your dog since there is a wide individual variation.