Page 1205 - Clinical Small Animal Internal Medicine

123 Urolithiasis in Small Animals 1143

phosphate urolithiasis in cats are thought to be similar to Prevention of Cystine Uroliths
VetBooks.ir those in dogs. priate for cystine urolith prevention. Thiol‐containing
Diets used for dissolution of cystine uroliths are appro­
drugs have been used to prevent recurrence of cystine
Cystine Uroliths
Cystine Uroliths in Dogs uroliths in dogs, at doses similar to those used for disso­
Medical dissolution of cystine in dogs consists of reduc­ lution. Older dogs are less likely to form cystine uroliths
ing cystine concentration in the urine and increasing its and it may be possible to stop or taper therapies as
solubility. As with all uroliths, increasing urine volume is patients mature. The risk of recurrence of these uroliths
beneficial for dilution of crystalloids. The solubility of is high because cystinuria is an inherited defect in some
cystine can be increased by making the urine pH alkaline affected dogs. Giger et al. observed that castration of
(approximately 7.0–7.5), either by feeding a specific diet mastiffs, Kromfohrlanders, and Irish terriers with non‐
or by treatment with potassium citrate. type I cystinuria drastically diminished the excretion of
Features of a diet thought to help recurrence of cys­ cystine and dibasic amino acids. Maintaining a negative
tine are: cyanide‐nitroprusside test may be used to monitor and
adjust therapy. In the subset of dogs with androgen‐
urine dilution
● dependent cystinuria, castration can resolve cystinuria.
low protein/purine levels (low protein or vegetable
● If cystinuria decreases two months after castration com­
protein) pared to baseline measurement (before castration), the
alkalinize urine – target pH of 6.8–7.0
● patient is less likely to have recurrence of cystine uro­
limit sodium intake
● liths. If cystinuria persists four months after castration, it
taurine and carnitine supplementation.
was probably not androgen dependent. Nitroprusside
●
Hill’s Prescription Diet Canine u/d and Royal Canin UC test and cystine crystalluria are less reliable tests than
Low Purine have been recommended because they alka­ urine cystine measurement to detect persistent risk of
linize the urine and reduce urine concentration. They are cystine uroliths formation.
also markedly protein restricted (low in sulfur‐containing For information on screening for cystinuria please
amino acids), which decreases cystine excretion by contact:
20–25% via reduction of cystine precursors. Dr Giger/PennGen Laboratories
Some dogs with cystinuria have increased renal excre­ School of Veterinary Medicine
tion of carnitine, and low‐protein diets increase the risk University of Pennsylvania
of carnitine deficiency and associated dilated cardiomy­ 3900 Delancey Street, Room 4013
opathy in cystinuric dogs. As such, carnitine supplemen­ Philadelphia, PA 19104
tation may be indicated. In addition, cystine is a precursor Website: http://research.vet.upenn.edu/penngen
for taurine synthesis, and taurine supplementation may Email: PennGen@vet.upenn.edu
be warranted in these patients. Tel: (215) 573‐7545 (Metabolic Lab)
Dissolution of cystine urolithiasis has been reported
by treating patients with a thiol‐containing drug without Silica Uroliths in Cats and Dogs
feeding a protein‐restricted diet. Thiol‐containing drugs Effective dissolution protocols have not been reported
react with cystine, resulting in its conversion to a more for silicate stones in small animals. The risk of silica uro­
soluble compound by a disulfide exchange reaction. lith recurrence is not well documented. In one study of
Thiol‐containing drugs include D‐penicillamine and 2‐ silica uroliths, 12% of dogs had a previous episode of uro­
mercaptopropionylglycine (2‐MPG) (tiopronin, Thiola®, lithiasis, but in most cases it was not known whether the
Mission Pharmaceuticals). Although both drugs are previous urolith was also composed of silica.
effective, metal chelation and gastrointestinal side‐ To reduce the risk of silica stone recurrence, it is rec­
effects of D‐penicillamine make it a less desirable choice. ommended to change the diet to one in which the vege­
2‐MPG, at a dosage of 15–20 mg/kg of body weight table content is limited. The recommendation is to avoid
divided and given orally twice daily, is the treatment of diets containing soybean hulls and corn gluten feed, and
choice, in combination with dietary modifications for to avoid the ingestion of soil. As with all uroliths,
dissolution and prevention of cystine calculi. Use of this increased water intake should be promoted to decrease
protocol resulted in dissolution of 60% of uroliths in one the resulting concentration of calculogenic material in
study within 1–3 months and was effective in 18/18 dogs urine.
in another. This drug has been reported to be associated
with side‐effects in dogs such as aggression, myopathy, Mixed and Compound Uroliths
anemia, proteinuria, thrombocytopenia, elevations of The management of compound uroliths is challenging
liver enzymes, and dermatologic changes. because they consist of layers containing different mineral