Cystinuria, with subsequent cystine urolith formation, results from a breed-related inherited disorder of renal tubular transport in dogs. Cystine stones are dissolved by means of dietary modification, administration of cystine-binding agents, or urinary alkalinization or neutralization (see Controlling Urine pH).
Tiopronin and -penicillamine are cystine-binding agents. Tiopronin has fewer adverse effects and is the recommended choice.
Both tiopronin and d-penicillamine can cause Coombs-positive anemia, thrombocytopenia (see Platelet Disorders), increased liver enzyme activity, glomerulonephritis, lymphadenopathy, cutaneous hypersensitivity, and delayed wound healing. Penicillamine also causes vomiting.
After cystine stones have been dissolved, a prevention protocol can be instituted. Dietary modification with or without urinary alkalinization may be enough to prevent stone formation; if uroliths recur, however, tiopronin may also be required.
The Cystine-Binding Agent Allopurinol for Treatment of Urinary Disease in Animals
Allopurinol is a synthetic isomer of hypoxanthine that binds to and inhibits the action of xanthine oxidase. It decreases the production of uric acid by inhibiting the conversion of hypoxanthine to xanthine and of xanthine to uric acid. The result is a decrease in serum and urine uric acid concentrations.
In combination with a low-purine diet, allopurinol is used to dissolve ammonium urate uroliths in affected Dalmatian dogs. Dosage should be decreased in dogs with renal insufficiency.
