Page 345 - Problem-Based Feline Medicine

18 – THE THIN, INAPPETENT CAT 337

Dietary management of chronic renal failure. ● The mechanisms of these effects are unclear, but
● Treatment of cats with chronic renal failure by may be hemodynamically mediated by causing
dietary modification has been proven to significantly renal vasodilation especially of the efferent arteri-
increase survival. Generally, commercially available ole, and reducing glomerular capillary pressure.
“renal diets” are recommended. These diets have ● Preliminary studies of ACE inhibitor use in natu-
restricted protein, calcium, sodium, phosphorus and rally occurring chronic renal failure in cats have
acid-load, and added potassium. shown significantly increased survival times for the
subgroup of renal-failure cats with urine protein/cre-
Dietary protein restriction is frequently advocated.
atinine ratios > 1.
● In moderate to severe chronic renal failure, con-
● By reducing glomerular pressure, ACE inhibition
trolled restriction of non-essential protein will
would be expected to cause a decrease in glomeru-
reduce the accumulation of nitrogenous waste prod-
lar filtration rate and so may increase azotemia.
ucts that are believed to contribute to the uremic
A rise in creatinine of > 50% warrants withdrawal
syndrome.
of the drug.
● More controversially, the use of a restricted protein
diet in early CRF may slow the rate of progression Treatment of renal secondary hyperparathyroidism
to end-stage renal failure by preventing maladaptive should be instituted in a staged manner.
changes in surviving nephrons. However, evidence
The cornerstone of therapy is dietary phosphate
for a beneficial effect of protein restriction on renal
restriction.
function in cats with early renal failure is not avail-
● After initiation of phosphate restriction, plasma
able.
phosphate levels usually stabilize at a lower level by
● Poor appetite and the decreased palatability of
2–8 weeks, however PTH concentrations may con-
restricted protein diets make mal-nutrition a seri-
tinue to decline without additional intervention.
ous problem in renal-failure patients. Monitor
● Proteinaceous foods are the main source of phos-
carefully for weight loss and decreasing muscle
phate in the diet, so phosphate restriction is gener-
mass.
ally combined with protein restriction.
● Dietary protein intake should be tailored to the
● The aim of dietary phosphate restriction is to
metabolic needs of the individual cat. Usually a diet
reduce plasma phosphorus to the lower limit of
containing at least 21% of gross energy as protein is
the reference range, the point at which the most
required (usual maintenance diets contain 35–55%
effective control of PTH secretion is usually
gross energy as protein). The goal is to maintain a
attained.
BUN of ≤ 29 mmol/L (80 mg/dl). In general, the
more severe the renal dysfunction, the greater the If after 4 weeks dietary management alone is not
protein restriction required, but protein should not achieving this, or if PTH concentrations are not
be decreased below 19–20% of gross energy decreasing, then intestinal phosphate-binding agents
(metabolizable energy). should be introduced to further restrict phosphate
intake.
A number of other dietary components have been stud-
● Intestinal phosphate-binding agents form non-
ied for their effect to modify the rate of progression
absorbable salts of phosphate, binding phosphate in
including calorie intake and fatty acid composition.
both the diet and intestinal secretions. To achieve
Dietary phosphate restriction is discussed under the sec-
efficient phosphate binding, the medication should
tion on renal secondary hyperparathyroidism.
be given, ideally mixed through the food or imme-
Angiotensin-converting enzyme (ACE) inhibitors diately before feeding.
may have a renoprotective effect, which is inde- ● Aluminum hydroxide should be dosed at 30–100
pendent of any effect on systemic blood pressure. mg/kg/day PO in divided doses with each meal,
ACE inhibitor therapy may also be useful in titrated to effect based on plasma phosphate concen-
reducing the degree of proteinuria in cats with trations. Dose can be increased to 200–300 mg/kg if
chronic renal failure. benazepril 0.25–0.5 mg/kg necessary to control phosphate. If the cat refuses to eat
PO q 24 h. it with food, a compounding pharmacy can formulate