Canine Xanthine

Often radiolucent when very small (<2mm). These stones become more visible as their size increases.

Hereditary xanthinuria is a rare autosomal recessive disorder of purine metabolism caused by mutations in xanthine dehydrogenase (Type I) or molybdenum cofactor sulfarase (Type II) genes, and causes xanthine uroliths. Breeds with hereditary xanthinuria include Toy Manchester Terrier, Cavalier King Charles Spaniel, English Cocker Spaniel, Dachshund, Chihuahua, and mixed breed dogs. Xanthine uroliths can also develop as an adverse consequence of xanthine dehydrogenase inhibitors (allopurinol), especially when given in higher doses and without dietary purine/protein reduction. Xanthine uroliths associated with allopurinol administration can be rapidly dissolved by stopping allopurinol and feeding a low-purine, urine-alkalinizing diet.

• Determine if xanthine dehydrogenase inhibitors (allopurinol) were administered. • Genetic tests for Type 1 (xanthine dehydrogenase deficiency) and Type 2 (molybdenum cofactor sulfurase deficiency) genetic variants.

• Discontinue or reduce xanthine dehydrogenase inhibitors. • Potassium citrate if urine pH is consistently <6.5 (starting dose: 75mg/kg q12-24h).

• Low purine/protein foods that produce neutral or alkaline urine (e.g. L/d, i/d Sensitive, u/d, HA vegetarian, others). If needed, feed canned therapeutic foods or add water to achieve a urine specific gravity <1.020.

Urinalysis every 3 to 6 months to adjust pH to ≥ 6.5, and urine specific gravity < 1.020. Medical imaging every 3 to 6 months to detect recurrence. Recurrence is an indication for further evaluation and alternative treatment strategies.

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Canine Xanthine