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An Urban Experience
concentrations of calculogenic substances
and decreasing dietary intake of calculogenic substances. Despite these measures, they do not guarantee prevention of urolith recurrence in all patients demonstrating that urolith formation is a complex process and many questions remain un- answered.
In 2016, the ACVIM released a consensus on management of urolithiasis in dogs and cats, which is available as an open source document at and summarized.8
canned food a with 2- mercaptopropionylglycine at
a dosage of 15–20 mg/kg PO q12 h successfully dissolves cystine stones.15 Cystine solubility increases with increasing urine pH. In vitro studies that achieved
a urine pH > 7.5 increased ef cacy of thiol-binding drugs to solubilize cystine in the urine. Administration of 2-mercaptopropionylglycine without modifying the diet
is associated with dissolution.15,16 Dissolution should be attempted cautiously in cats because of intolerance of 2-mercaptopropionylglycine. Dogs and cats without clinical signs but with nondissolvable uroliths too
large to pass into the urethra or too irregular to cause urethral obstruction need only periodic monitoring and appropriate client education. With the onset of clinical signs (eg, hematuria, dysuria, UTI, urolith removal should be considered. Educate clients about clinical signs of urinary obstruction. In order to minimize patient discomfort and unnecessary damage to healthy tissues, nonsurgical removal methods (eg, dissolution, basket retrieval, lithotripsy, percutaneous cystolithotomy)
should be considered for nonclinical urocystoliths that are likely to cause urinary obstruction. Urethroliths should be managed by intracorporeal lithotripsy and basket retrieval.17 In male dogs and cats urethroliths can be urohydropropulsed retrograde back into the bladder and retrieved by percutaneous cystolithotomy or cystotomy.18 Urethrostomy can be considered to minimize future urethral obstruction in highly recurrent stone-forming animals. Rigid adherence to strategies
to prevent urolith recurrence, however, should be considered  rst. Because of the high frequency of morbidity and adverse effects associated with urethral surgery, urethral surgeries are discouraged except under few circumstances.
Only problematic nephroliths require treatment such as out ow obstruction, recurrent infection, pain, and those enlarging to the point of causing renal parenchymal compression, should be considered for removal in
dogs and cats. Dissolution only should be considered
for nonobstructive nephroliths or if the obstruction can be concomitantly alleviated or bypassed (eg, urethral stenting). The presence of nephroliths in cats with chronic kidney disease did not signi cantly affect the progression of renal disease.19 Treatment for other nephroliths potentially amenable to dissolution should
be addressed on a case-by-case basis considering the stability of kidney function and the likelihood of complete removal or dissolution. Approximately 20–30% of upper urinary tract uroliths in dogs are suspected to be struvite for which dissolution should be effective. Rapid control of infection while avoiding surgical urolith extraction should maximally preserve kidney function.20 Dissolution should not be attempted in cats with obstructive upper urinary tract uroliths. Over 90% of nephroliths and ureteroliths in cats are composed primarily of calcium oxalate. Delaying
Struvite uroliths (ie, moderately radiopaque uroliths in dogs with alkaline urine and a urinary tract infection caused by urease-producing bacteria (such as Staphylococcus spp), and moderately radiopaque uroliths in cats with approximately neutral urine pH) should be medically dissolved unless (1) medications
or dissolution foods cannot be administered or are contraindicated, (2) uroliths cannot be adequately bathed in modi ed urine (eg, urinary obstruction,
large solitary urocystoliths occupying almost all of
the urinary bladder), or (3) uncontrollable infection despite appropriate medical management and owner compliance. Medical dissolution for struvite uroliths is highly effective and infection-induced struvite usually dissolve in 8 weeks while sterile struvite dissolve in
less than 2–5 weeks.9,10 Urocystoliths small enough
to pass through the urethra should be removed by medical dissolution, voiding urohydropropulsion,
basket retrieval, or other extraction procedures that
do not involve surgical intervention. Urocystoliths too large to pass through the urethra should be removed
by medical dissolution, intracorporeal laser lithotripsy,
or percutaneous cystolithotomy.11,12 Consider
medical dissolution of urate uroliths before removal. Hyperuricosuria, concentrated urine, and acidic urine
the predominant factors driving urate urolith formation.13 In most dogs and cats, uric acid is transported to the liver where it is metabolized by uricase to allantoin.
A defective uric acid transporter (ie, SLC2A9 genetic mutation) and hepatic porto-vascular anomalies
are common causes for hyperuricosuria and urate urolithiasis.14 However, for some animals, especially cats, the cause(s) for hyperuricosuria and urate urolith formation remains idiopathic. Dissolution of urate uroliths in dogs usually is accomplished within 4 weeks by feeding a purine-restricted, alkalinizing, diuretic diet, and administering a xanthine oxidase inhibitor (ie, allopurinol: 15 mg/kg PO q12 h).13 Dissolution has not been possible in cats or in dogs and cats with uncorrected liver disease. Cystine uroliths form, in part, because
of decreased proximal tubular reabsorption of cystine. Consumption of a decreased protein, urine-alkalinizing,

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