Page 1201 - Clinical Small Animal Internal Medicine

123 Urolithiasis in Small Animals 1139

should be considered in dogs that have persistent cal­ to eradicate UTI throughout the diet treatment and is
VetBooks.ir cium oxalate crystalluria or recurrence of calcium oxa­ likely the most important facet of medical dissolution of
struvite uroliths. The average time of dissolution of
late urolithiasis despite dietary therapy. This drug can
cause severe gastrointestinal (GI) side‐effects.
Decreased serum vitamin B6 concentrations were canine infection‐induced struvite urocystoliths on the
Hill’s s/d diet was approximately 2–3 months in dogs.
detected in a small number of oxalate stone‐forming This diet should not be continued beyond this time as it
dogs compared to nonstone formers. Based on this study, is not meant to be a long‐term diet.
supplementation of vitamin B6 (2–4 mg/kg PO q24–48h) Feeding small meals throughout the day rather than
could be considered in repeat stone formers. Vitamin C one or two large meals may prevent postprandial alkaline
is converted to oxalate, so vitamin C supplementation tide and is associated with more acidic urine production
may contribute to hyperoxaluria and increased risk of and less struvite crystalluria.
calcium oxalate urolithiasis. Vitamin D supplementation The use of urinary acidifiers has been suggested in
increases intestinal absorption of calcium, thereby pro­ dogs because struvite and hydroxyapatite are most solu­
moting hypercalciuria and increased risk of calcium oxa­ ble in acidic urine (pH 6.0–6.5). In most dogs with infec­
late urolithiasis. tion‐induced struvite uroliths, eradication of the UTI
Dietary recommendations for prevention of calcium with dietary modification will return urine pH to the
oxalate uroliths in cats are thought to be similar to those acidic range. Use of urine acidifiers in these cases is not
in dogs, although higher salt levels are sometimes used indicated.
to aid increased urination. In addition, one two‐year Most clinical symptoms of lower urinary tract inflam­
study in cats showed no significant difference between mation resolve after the first 10 days of antibiotic and
two diets that differed in calcium and magnesium con­ diet therapy. However, antibiotic and diet therapy should
tents and in urinary pH potential. Primary hyperoxaluria be continued for one month beyond radiographic evi­
can occur in cats. Examples of diets that have undergone dence of urolith dissolution or one month beyond stone
urinary testing for reduction of calcium oxalate include removal. Although feeding a dissolution diet is advised,
Hill’s c/d Multicare (canned and dry), Purina UR St/Ox struvite uroliths have been managed with effective con­
(canned and dry), and Royal Canin S/O (canned, chunks trol of the underlying UTI alone.
and gravy, and dry).
Prevention and Follow‐Up of Struvite Uroliths in Dogs
Struvite Uroliths Examination of urine pH, specific gravity, sediment, and
Dissolution of Struvite Uroliths in Dogs culture is recommended at 5–7 days after starting
Struvite uroliths in dogs are almost always due to infec­ therapy, and then every four weeks until the stones are
tion with a urease‐producing organism, and as such dissolved (Table 123.3). Once dissolution (based on radi­
medical dissolution of struvite depends on the careful ographic evidence) or removal is accomplished, a urine
elimination of infection together with specific dietary culture should be obtained at four and eight weeks later,
therapy. with cessation of antibiotic and dietary therapy four
The calculolytic diets most commonly advised for weeks after resolution. Urine culture and radiographs
struvite stone dissolution in dogs are the Prescription should then be repeated every three months for one year
Diet Canine s/d (Hill’s Pet Products, Topeka, Kansas) and then every six months thereafter. The goal is to
and Royal Canin S/O. Of these two, the Prescription Diet maintain the average urine pH 6–6.5, the average urine
Canine s/d has been used successfully to induce dissolu­ specific gravity <1.020, the sediment free of significant
tion of struvite calculi in dogs. The Royal Canin diet was crystalluria, and the dog free of bacterial infection.
effective for struvite dissolution in an ex vivo setting. In dogs with a history of urinary tract infections, pro­
When using the Hill’s s/d diet, laboratory changes in active and routine urine culture and susceptibility is rec­
the patient will occur that can also be used to monitor ommended. This is particularly important if co‐morbid
owner compliance. The diet is low in phosphorus and situations arise (e.g., hyperadrenocorticism, renal dis­
protein which reduces urea, phosphorus, and serum ease) that may predispose to the development of a uri­
albumin. Mild increases in serum alkaline phosphatase nary tract infection.
may also be present. These changes are not expected The need for specific ongoing dietary therapy for pre­
with Royal Canin S/O. Both diets promote undersatura­ vention of struvite uroliths in dogs is unknown. Since the
tion of the urine with ions necessary for the formation majority of dogs have infection‐induced struvite uro­
of struvite uroliths and, thus, promote dissolution of liths, it is likely that effective control and prevention of
existing struvite calculi. Both diets also contain a high infection alone would be sufficient to prevent recur­
NaCl content in order to induce diuresis and dilution of rence. However, dietary therapy to lower urine concen­
urine. Concurrent antibiotic therapy is recommended tration (canned food or addition of water) or minimize