Page 728 - Small Animal Internal Medicine, 6th Edition

700 PART V Urinary Tract Disorders

from the previous diet to the prescribed diet over 2 to 4 with CKD. The kidneys can maintain normal serum potas-
weeks is recommended. On a low-protein diet, the BUN sium concentrations at 5% of normal GFR if urine volume
VetBooks.ir concentration will decrease as a result of dietary modifica- is adequate. Hypokalemia in dogs and cats with CKD may
be treated with oral potassium gluconate or potassium
tion alone and will no longer be a good indicator of renal
function. SCr is not influenced by diet. It is, however, affected
Phosphorus restriction
by loss of muscle mass, which can confound interpretation citrate.
of SCr in cachectic animals with CKD. Early phosphorus restriction in CKD has been shown to
The nutritional needs of cats differ from dogs. Dogs blunt or reverse renal secondary hyperparathyroidism. In a
require that a minimum of approximately 5% of calories study of dogs with 94% nephrectomy that were fed diets
come from protein, whereas cats require that a minimum of containing 17% protein with 0.5% or 1.5% phosphorus, pro-
20% of calories come from protein. These represent minimum gression was more rapid and outcome worse in the dogs fed
requirements and do not provide for nitrogen reserves. the higher phosphorus diet. Tubulointerstitial lesions also
Healthy adult cats typically maintain lean body mass on 32% were worse in dogs on the higher phosphorus diet. In another
to 34% of calories from protein. Cats also seem to prefer diets study, renal secondary hyperparathyroidism was docu-
higher in fat and require a source of taurine in their diet. mented in 84% of cats with naturally occurring CKD and, as
Stable body weight, stable serum albumin concentration, assessed by serum phosphorus and PTH concentrations,
and decreased BUN concentration are indications that a low- responded to dietary phosphorus restriction. Because
protein diet is being used effectively. Accelerated weight extremely phosphorus–depleted diets are unpalatable,
loss, on the other hand, indicates the need for dietary phosphorus–binding agents may be given orally to trap
modifications. phosphorus in the gut and hasten its excretion. These drugs
Adequate nonprotein calories to maintain body condition should be given with meals or within 2 hours of feeding to
should be provided by carbohydrate and fat. Approximately maximize their effectiveness. When CKD is diagnosed,
60 kcal/kg/day are recommended as a general guideline, but phosphorus restriction is initiated by feeding a low-
older animals may eat fewer calories normally (e.g., 40 kcal/ phosphorus, low-protein diet. If necessary, oral phosphorus–
kg/day). Supplementation of the diet with ω-3 PUFAs may binding agents can be added as necessary to the treatment
be renoprotective. Increasing the amount of ω-3 PUFAs rela- regimen for additional reduction in serum phosphorus
tive to ω-6 PUFAs in the diet decreases the production concentration.
of proinflammatory, platelet-aggregating, vasoconstrictive In humans, chronic aluminum intoxication causing bone
prostaglandin (PG) TXA2 and increases the production of disease and encephalopathy has been recognized as an
vasodilatory prostaglandins (PGE, PGI). Studies of dogs important complication of aluminum-containing phospho-
with remnant kidneys have shown beneficial effects of sup- rus binders; it is thought that there is no safe dosage of
plementation, including decreased proteinuria, preservation aluminum-containing phosphorus binder that will provide
of GFR, and less severe renal morphologic changes. These sufficient phosphorus restriction without risking aluminum
studies used very low ω-6–to–ω-3 ratios, which may not be intoxication. Consequently, other phosphorus binders have
easily achievable using commercial diets. An ω-6–to–ω-3 replaced aluminum-containing phosphorus binders in
ratio of 2 : 1 may be reasonable in a renal diet. Alternatively, humans with CKD. It is not yet clear that aluminum intoxi-
the diet can be supplemented with 1 to 5 g/day of ω-3 PUFAs. cation is a problem in dogs and cats with CKD, but it has
Increased fractional sodium excretion allows mainte- been reported in two dogs with AKI. Aluminum-containing
nance of sodium balance during the course of progressive phosphorus binders are still used by many veterinary clini-
CKD. Dietary sodium restriction may be advisable in dogs cians in dogs and cats with CKD. Aluminum hydroxide
with CKD and hypertension and in those with glomerular (Amphojel) can be used at a dosage of 45 mg/kg q12h given
disease that have sodium retention and edema. Patients with with food. In general, an attempt should be made to maintain
CKD are less flexible in adjusting to changes in dietary the serum phosphorus concentration at less than 5.0 mg/dL.
sodium load. Many commercial pet foods provide more If preferred, calcium carbonate can be used instead, at a
sodium than needed, often about 1%, and commercial prod- starting dosage of 45 mg/kg q12h given with food. It has the
ucts marketed for dogs and cats with CKD provide approxi- advantage of not containing aluminum, which may be toxic
mately 0.2% to 0.3% sodium. if absorbed from the GI tract. Calcium acetate is more effec-
The metabolic acidosis of CKD generally is well compen- tive than the aluminum- or other calcium-containing phos-
sated. If metabolic acidosis is severe (serum bicarbonate con- phorus binders and may be used at a slightly lower dosage.
centration ≤ 12 mEq/L), sodium bicarbonate may be added The animal should be monitored for the development of
to the treatment regimen. The dosage should be adjusted to hypercalcemia whenever calcium-containing phosphorus
maintain the serum bicarbonate concentration at 14 mEq/L binders are used. Constipation may be a complication of
or higher and the additional sodium intake should be taken phosphorus binders and may be managed by addition of
into consideration. Potassium gluconate and potassium polyethylene glycol 3350 (Miralax) or lactulose to the treat-
citrate are alternative sources of alkali that provide potas- ment regimen. Sevelamer HCl is a phosphorus binder that
sium and do not pose the problem of an additional sodium does not contain aluminum or calcium. A dosage of 10 to
load. Hyperkalemia usually is not a problem in dogs and cats 20 mg/kg q8h given with food may be considered for dogs