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We report a case of ammonium acid urate stone due to laxative abuse. A 27-year-old female complained of left flank pain. Computed tomography revealed bilateral ureter stones (right 16.5 x 9.0 mm; left 4 mm), while left ureter stone was radiolucent on the plain X ray film. Bilateral hydronephrosis was seen, but no therapy was performed for the right stone, because 99mTc-MAG3 scintigraphy revealed that right kidney had no function. The left stone was successfully removed by transurethral approach. The stone was revealed to be an ammonium acid urate by infrared spectrophotometry. She had been taking many laxatives (bisacodyl, sennoside, aloe extract) for 12 years to control her body weight. Ammonium acid urate stones are rarely seen in developed countries. We have reviewed 9 cases in Japan, describing ammonium acid urate stones due to laxative abuse. Among these patients, 24-hour urine volume and excretion in urinary sodium were decreased, and serum aldosterone was increased. The involvement of laxative abuse should be considered when ammonium acid urate is formed in a woman with a low body mass index.

As calcium oxalate stones are the most important component in urolithiasis, an experimental model has to be designed to clarify the pathogenesis and aid in their prevention. Hyperoxaluria as well as hypercalciuria were produced in rats by administering ethylene glycol (0.5%, in drinking water administered ad libitum) and 1-alpha (OH) D3 (0.5 micrograms/rat given every other day), respectively, for three to four weeks. Neither drug alone produced stones efficiently as did the combination regimen of these two compounds. The occurrence of stones was 77.3%, and with only a moderate degree of renal functional impairment. Biochemical and histological data were obtained using this model.