Anorexia is the most common cause of calorie malnutrition in cats with chronic renal failure (CRF) and it is one of the most frustrating aspects of patient management. Metabolic deficits and excesses, gastrointestinal dysfunction, and feeding management problems (eg, force feeding and sudden diet change) can all contribute to the anorexia associated with CRF (Table 1).
METABOLIC DEFICIENCIES AND EXCESSES
In many cases, anorexia can be minimized by correction of metabolic deficits and excesses. For example, dehydration, hypokalemia, hypocalcemia, hyperphosphatemia, metabolic acidosis, anemia, and hypertension are at least partially correctable metabolic disorders associated with CRF that can decrease appetite. Cats with acutely decompensated CRF will almost always require intravenous fluid deficit replacement.
On the other hand, subcutaneous fluid supplementation at home in mildly dehydrated cats may go a long way toward improving the appetite. Most cats with CRF have mild to moderate whole body potassium depletion that can cause muscle weakness, gastrointestinal ileus, and anorexia. The best route for potassium replacement is oral (approximately 2.2 mEq/kg body weight/d), however KCl can also be added to parenteral fluid solutions in anorexic cats.
Hypocalcemia, if present, can often be managed by controlling hyperphosphatemia and oral calcium and calcitriol if necessary. The hyperphosphatemia associated with CRF is best controlled with phosphorus-restricted diets and enteric phosphate binders. Ultra low-dose calcitriol is an additional, but controversial treatment that may help control hyperphosphatemia.
Potassium citrate or sodium bicarbonate diets have already been appropriately supplemented. An appropriate goal for alkalinization therapy is a urine pH between 7.0 and 7.5. The nonregenerative anemia of CRF can also decrease the quality of life and contribute to a patient’s anorexia. Human recombinant erythropoietin is very effective at reversing this anemia, however, this “foreign” protein can be antigenic in approximately 30% of cats.
Finally, controlling CRF-associated systemic hypertension with calcium channel blockers or angiotensin-converting enzyme inhibitors may also help improve appetite.
With regards to gastrointestinal dysfunction, metoclopramide and H2 receptor blockers (ranitidine and famotidine) are the drugs of choice to decrease chemoreceptor trigger zone stimulation and gastric hyperacidity. Managing constipation and dental/gingival disease, if present, are also important considerations.
Once metabolic and gastrointestinal disorders have been addressed, benzodiazepines (diazepam and oxazepam) and serotonin antagonists (cyproheptadine) can be used to stimulate appetite. Interestingly, human recombinant erythropoietin, apparently independent of its effects on anemia, is also a potent appetite stimulant in cats.
GETTING CRF CATS TO EAT
Dietary variety, frequent feeding of small quantities of moist/wet cat foods, using animal sources of protein with meat and fat flavors, warming the food, and using flavoring agents (clam juice, tuna juice, baby foods, and garlic) are additional strategies for treating anorexia. Any dietary change should be performed gradually.
In some cases, feeding tubes are necessary to insure adequate caloric intake. Cats usually tolerate gastrostomy tubes extremely well and these tubes can be left in place for months. If vomiting can be controlled, gastrostomy tubes allow the owner to administer calories and fluid to the patient with very little stress compared to forcefeeding and subcutaneous fluid therapy.In many cases, providing calories via tube feeding reverses the downward catabolic spiral of CRF cats and makes them feel good enough to eat on their own.