Page 815 - Small Animal Clinical Nutrition 5th Edition

Canine Purine Urolithiasis 845

tacaval shunt in a three-month-old female miniature schnauzer
Table 39-7. Expected changes associated with dietary and
VetBooks.ir (Osborne et al, 2000). However, the condition of the patient medical therapy of purine uroliths. During Prevention
resulted in a marked reduction of urine uric acid concentration
and factors related to anesthesia and surgery may preclude
urolith removal at the time the anomalous portal vessels are Factors Pre-therapy therapy therapy
Polyuria ± 1+ to 3+ 1+ to 3+
corrected. In this situation, postsurgical dietary and medical Pollakiuria 0 to 4+ ↑ then ↓ 0
therapy designed to dissolve uroliths should be considered. Hematuria 0 to 4+ ↓ 0
Urine specific Variable 1.004 to 1.015 1.004 to 1.015
Also, some types of portal vascular anomalies are not amenable
gravity
to surgical correction. If the uroliths cause unacceptable signs of Urinary pH <7.0 >7.0 >7.0
urinary tract disease, they should be surgically removed and Pyuria 0 to 4+ ↓ 0
Purine (urate) 0 to 4+ 0 Variable
postsurgical preventive measures should be initiated. Voiding
crystals
urohydropropulsion may be used to remove small urocystoliths Bacteriuria 0 to 4+ 0 0
(Figure 38-5 and Table 38-7) (Lulich et al, 1993). Bacterial culture 0 to 4+ 0 0
of urine
Urea nitrogen Variable ≤15 ≤15
(mg/dl)
REASSESSMENT Urolith size and Small to large ↓ 0
number
Ammonium urate urocystoliths have a propensity to move into
the urethra of dogs. This finding may be related to their small
size, round to ovoid shape and smooth surface. If small enough, required to perform the procedure, 3) virtually all uroliths can
they readily pass through the urethra. However, they often be visualized, including their size, shape and number and 4)
become lodged behind the os penis of male dogs. Owners uroliths may be retrieved through the catheter and submitted
should be informed of this likelihood and given a written sum- for quantitative analysis. If retrograde double-contrast urethro-
mary of associated clinical signs. Urethroliths causing clinical cystography is used to monitor dissolution of radiolucent ure-
signs may be easily returned to the bladder lumen by urohy- throcystoliths, appropriate prophylactic antibiotics should be
dropropulsion (Figure 38-5 and Table 38-7) (Lulich et al, administered around the time of urinary tract catheterization to
1993), or removed by lithotripsy. The physical characteristics minimize iatrogenic UTIs. Excretory urography or ultrasonog-
that permit passage of these uroliths into the urethra also facil- raphy may be used to monitor dissolution or recurrence of urate
itate their removal from the urethra. nephroliths.
When attempting dietary and medical dissolution of urate Urinary pH should be monitored at appropriate intervals
uroliths, owners should be counseled to adhere strictly to feed- (Table 39-7). Periodic evaluation of urine sediment for crystal-
ing the low-purine urate litholytic food. Consumption of a luria should also be considered. Ammonium urate crystals
high-purine food by dogs, while receiving allopurinol, will re- should not form in fresh urine if therapy has been effective in
sult in formation of a xanthine shell around urate uroliths or promoting formation of urine that is undersaturated with
formation of xanthine uroliths (Figure 39-3) (Bartges et al, ammonium ions and uric acid. Periodic evaluation of serum
1992; Ling et al, 1991; Osborne et al, 1986a). Xanthine uroliths urea nitrogen concentration, serum uric acid concentration and
may not dissolve. However, spontaneous dissolution of xan- (if possible) urine uric acid concentration is recommended.
thine shells and underlying uroliths may occur by discontinu- Reduction of serum urea nitrogen concentration below pre-
ing allopurinol and continuing the low-purine litholytic food treatment values (usually <10 mg/dl in previously nonazotemic
(Bartges et al, 1994). Alternatively, dissolution of urate uroliths patients), reduction of urine specific gravity (usually <1.020)
may occur as a result of feeding a low-purine litholytic food and and an increase in urinary pH (usually >7.0) indicate owner and
administering a lower dose of allopurinol than that associated patient compliance with dietary therapy (Table 39-7).
with formation of xanthine shells. Reductions in serum and urine uric acid concentrations also
Because allopurinol and its metabolites are excreted from the indicate compliance with recommendations for dietary and
body primarily in urine, the drug should be used cautiously in allopurinol therapy.
patients with renal dysfunction (Bartges, 1993; Hande et al, Determination of urine urate-to-creatinine ratios in random-
1984). Reduction in the dosage of allopurinol is recommended ly collected single urine samples has been recommended to aid
for human patients with primary renal failure. Pending further in diagnosis and to monitor medical and dietary therapy of
studies, a similar recommendation should be applied to dogs dogs with urate uroliths (Schaible, 1986; Senior, 1989).
with primary renal failure. However, in a controlled study, spot urine urate-to-creatinine
The size of uroliths should be periodically monitored by sur- ratios correlated poorly with 24-hour urine uric acid excretion
vey and (if necessary) double-contrast radiography or ultra- in healthy non-urolith-forming beagles (Bartges et al, 1994a).
sonography (Table 39-7). It is more difficult to monitor Although urine urate-to-creatinine ratios decrease significantly
changes in size and number if the uroliths are radiolucent. in dogs with urate uroliths given allopurinol (Moentk et al,
Double-contrast cystography is superior to ultrasonography 1994), they do not correlate with 24-hour urine uric acid excre-
because: 1) it is minimally invasive, 2) sedation is usually not tions in these dogs, nor are they useful in predicting urolith dis-