Chapter 57 Treatment of Chronic Renal Failure in Nondomestic Felids
Chronic renal failure (CRF) is a significant cause of morbidity and mortality of older felids in captivity. Chronic renal failure is frequently caused by chronic pyelonephritis, glomerulosclerosis, or amyloidosis. Because the renal changes resulting in CRF are often irreversible, treatment is aimed at slowing the progression of the disease and alleviating signs. Prompt and consistent treatment of CRF can improve the cat’s quality of life and longevity.
Clinical signs of CRF often include polyuria, polydipsia, decreased appetite, weight loss, poor pelage condition, salivation, oral ulceration, vomiting, and dehydration. Nondomestic felids with suspected renal failure should be evaluated with a thorough physical examination and collection of clinical pathology samples. Sample collection should include whole blood for a complete blood cell count (CBC), serum or plasma for chemistry analysis, urine (ideally using cystocentesis) for a complete urinalysis, and a percutaneous kidney biopsy (consider performing a coagulation screen before biopsy) to stage the severity of the disease and monitor response to treatment. Urine should be submitted along with serum for fractional clearance determination as well as bacterial culture.
Clinical pathology may show a mild, nonregenerative anemia with a neutrophilia or normal white blood cell (WBC) count. Serum chemistry results often reveal increases in blood urea nitrogen (BUN), creatinine, phosphorus, and cholesterol and decreases in calcium, potassium, albumin, and total protein. Most nondomestic felids may be trained to allow blood collection with protected manual restraint (or squeeze cage), or with no restraint, and free-catch clean urine collection. This allows serial samples to be collected to monitor response to therapy.
The presence of normal urine specific gravity does not rule out significant glomerular disease (glomerulotubular imbalance). Normal urine protein/creatinine ratio is 0.4 to 0.5. A ratio greater than 1.0 indicates significant proteinuria.
In domestic cats the urine protein/creatinine ratio and fractional excretion (FE) of potassium, calcium, phosphorus, and sodium have been shown to increase in CRF. These increases are noted before significant increases in BUN and serum creatinine. In general, the FE ratios have been shown to be more sensitive indicators of renal damage than the urine protein/creatinine ratio. These tests have been used in cheetahs.4 The urine protein/creatinine ratio (normal <1.0) requires the collection of only a urine sample, whereas the FE values require a urine sample and matched serum/plasma sample. Fractional excretion ratios are calculated using the following formula:
When possible, treatment should be directed against the primary cause of the renal failure, as well as any complications identified. Careful consideration should be given to discontinuing all nephrotoxic drugs that the felid is currently receiving. A thorough physical examination supplemented with thoracic and abdominal radiography (small, irregularly shaped kidneys) and ultrasonography (increased cortical density and loss of corticomedullary boundary) should be completed to rule out other diseases or causes of chronic inflammation.
Chronic pyelonephritis is common in felids and frequently does not cause a significant neutrophilia on the CBC. Cats suspected of having pyelonephritis benefit from long-term antibiotics or pulsed antibiotics. Amoxicillin or amoxicillin plus clavulanate (Clavamox; 20 mg/kg orally [PO] twice daily [bid] or three times daily [tid]) or enrofloxacin (Baytril; 2.5-5.0 mg/kg PO once daily [sid]) has been used successfully in many felids, with treatment for 2 to 4 weeks every 3 months. Reducing the causes of chronic inflammation may be beneficial in slowing the progression of glomerulosclerosis and amyloidosis. Nonsteroidal antiinflammatory drugs (NSAIDs) may be indicated to reduce inflammation byproducts. Colchicine (0.01-0.03 mg/kg/day PO) may reduce serum amyloid A protein release.1
Common complications of CRF in felids include dehydration, anorexia, proteinuria, hypertension, hypokalemia, hyperphosphatemia, vomiting, and uremia. Aggressive treatment of these complications before or immediately on their appearance may improve the quality of life for the cat.
Dehydration appears to be the most common event that results in decompensation of a felid with CRF. Chronic renal failure results in a polyuria from a decrease in urine-concentrating ability. A compensatory polydipsia offsets the polyuria. If anorexia, vomiting, or diarrhea interrupts the polydipsia, dehydration is likely to occur, resulting in rapid and severe worsening of renal function. Because of the polyuria, daily fluid requirements for cats with CRF are higher than fluid requirements for normal cats.
Fluid therapy is essential to prevent decompensation of the CRF. Felids are more likely to drink water if the water bowl is refilled frequently and the water temperature is cool, but not cold. Ice may be added to the water bowl in hot climates. Some felids will more readily ingest ice cubes with meat juices added. Other cats will drink more water if a small amount of chicken broth (low sodium) is added. Water may be added to many commercial diets, including chunk muscle meat, and injected into whole-prey items to increase their water content.
Most nondomestic felids may be trained to accept subcutaneous fluid administration with protected manual restraint (or squeeze cage), or with no restraint. Fluid boluses as low as 20 mL/kg, once to four times a week, may significantly improve hydration status in some cats. Cheetahs will usually tolerate the daily administration of 1 to 4 L of subcutaneous fluids. Frequently the benefits of the quick administration of subcutaneous fluids using operant conditioning or manual restraint outweigh the risks of the procedure.