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Are Xanthine Stones Dissolvable?

The answer depends on the underlying cause.  Xanthine, an intermediate-byproduct of purine catabolism, is rarely found in urine or stones because it is metabolized to uric acid and then allantoin, a water soluble end-product that is excreted in urine.  Hereditary Xanthinuria is a rare autosomal recessive disease caused by loss of xanthine dehydrogenase (XDH) or molybdenum cofactor sulfurase (MOCOS) genes. Acquired Xanthinuria is a potential adverse consequence of allopurinol, a xanthine dehydrogenase inhibitor administered to treat leishmaniasis and prevent urate uroliths.  In acquired xanthinuria, xanthine uroliths are dissolvable. Hereditary xanthine uroliths are not dissolvable.

photo of a dalmatianCase Example: Jake is a 2-year-old male Dalmatian diagnosed with urate uroliths. Following urolith removal, Jake was prescribed allopurinol (15mg/kg /day) to reduce urate stone recurrence.  However, a diet change was not recommended.  A 2-month recheck identified urolith recurrence (figure 1); uroliths were much larger than his previous ones. During the recheck, small uroliths were retrieved with a urinary catheter and submitted for quantitative analysis.  Recurrent stones were composed of 100% xanthine.  With this new information, allopurinol was discontinued and Jake was prescribed a low purine, urine-alkalinizing diet (Prescription diet u/d).  Radiographs taken one month later revealed that all xanthine stones had dissolved (figure 2).  To prevent future urate urolith recurrence, allopurinol was prescribed at a lower dose (7 mg/kg/day) and the low-purine diet was continued. Read more on allopurinol and urate uroliths.
double contrast radiographs dog with xanthine uroliths Figure 1.  Double contrast cystogram showing xanthine uroliths in the urinary bladder of a male Dalmatian following allopurinol administration.

double contrast cystogram radiograph no uroliths visible.
Figure 2. Double contrast cystogram of the dog in figure 1 one month after stopping allopurinol and feeding a low purine diet.  Xanthine uroliths rapidly dissolved.

See Also our Canine Xanthine Recommendations