Page 935 - Small Animal Clinical Nutrition 5th Edition

Feline Lower Urinary Tract Diseases 967

VetBooks.ir Box 46-9. Additional Treatments for Calcium Oxalate Urolithiasis.

VITAMIN B
6
Deficiency of vitamin B has been associated with increased uri-
6
nary oxalate excretion; however, it has not been shown to cause
calcium oxalate uroliths. Additional vitamin B is unlikely to benefit
6
cats eating most commercial foods; however, if a cat with calcium
oxalate uroliths is being fed a homemade food, it would be appro-
priate to supplement with vitamin B (2 to 4 mg/kg body weight
6
orally once daily).
THIAZIDE DIURETICS
Thiazide diuretics are known to cause renal tubular reabsorption of
calcium, resulting in decreased urine calcium excretion, which may
decrease likelihood of calcium oxalate urolith recurrence. Thiazide
diuretics have been used for treatment of calcium oxalate urolithi-
asis in people but no studies have been reported in cats with cal-
cium oxalate uroliths. In a blinded, placebo-controlled crossover
study performed with healthy cats, administration of hydrochloroth-
iazide suspension (1 mg/kg orally q12h) was associated with sig-
nificantly decreased urinary saturation of calcium oxalate com-
pared with placebo. For cats with recurrent calcium oxalate uroliths
despite feeding a therapeutic food and increasing water intake, thi-
azide diuretics may be considered. Thiazide diuretics should not be
used in cats with hypercalcemia. Figure 1. Schematic depicting the role of citrate in binding intes-
tinal calcium (Ca) ions and reducing calcium absorption, promoting
POTASSIUM CITRATE formation of alkaline urine and preventing calcium oxalate (CaOx)
Increased urinary citrate may form soluble complexes with calcium, urolith formation.
making it unavailable to form calcium oxalate uroliths. Citrate
inhibits calcium oxalate crystal formation by promoting formation of dietary citrate may have little effect on urinary citrate. Feeding up
alkaline urine and by forming complexes with calcium (Figure 1). to 100 mg of citric acid/kg body weight to cats has been shown to
When citrate complexes with calcium, ionic calcium concentration have little effect on urine citrate concentrations. Effects of potassi-
and urine saturation with calcium oxalate are reduced. um citrate alone on urinary calcium oxalate saturation or urolith
Hypocitraturia is reported to occur in 19 to 63% of human recurrence have not been evaluated in healthy cats or cats with cal-
a
patients with calcium oxalate urolithiasis; however, frequency of cium oxalate uroliths. One therapeutic food containing potassium
hypocitraturia in cats with calcium oxalate urolithiasis is unknown. citrate was associated with decreased urinary calcium oxalate sat-
Changes in acid-base status influence renal handling of citrate. uration in cats with calcium oxalate uroliths. Potassium citrate (50
Metabolic acidosis virtually eliminates urinary citrate excretion by to 75 mg/kg body weight orally q12h with food) should be consid-
promoting citrate oxidation. Acidosis favors influx of citrate into ered in cats that have recurrent calcium oxalate uroliths despite
renal mitochondria and inhibits efflux of citrate from mitochondria. using other measures (e.g., feeding moist food or therapeutic food,
Tubular and peritubular citrate uptake increases when cytosolic cit- increased water intake).
rate concentration decreases. Increased reabsorption of citrate
reduces urinary citrate excretion. The citrate in urine is the small ENDNOTE
quantity that escapes reabsorption. In metabolic alkalosis, urinary a. Hill’s Prescription Diet x/d Feline. Hill’s Pet Nutrition Inc., Topeka,
citrate increases because mitochondrial uptake and thus oxidation KS, USA.
of citrate is reduced, cytosolic citrate concentration increases,
reabsorption decreases and urinary excretion of citrate increases. The Bibliography for Box 46-9 can be found at
Thus, depending in part on the acid-base status of the patient, www.markmorris.org.

c. Feline Control pHormula Waltham Veterinary Diet. g. Medi-Cal Dissolution Formula. Veterinary Medical Diets,
Waltham, Vernon, CA, USA. Guelph, Ontario, Canada.
d. Cystease. Ceva Animal Health, Chesam, United Kingdom.
e. Hill’s Prescription Diet x/d Feline. Hill’s Pet Nutrition Inc., REFERENCES
Topeka, KS, USA.
f. Hill’s Prescription Diet s/d Feline. Hill’s Pet Nutrition Inc., The references for Chapter 46 can be found at
Topeka, KS, USA. www.markmorris.org.