The effects of ammonium chloride, methenamine hippurate and ascorbic acid on urinary pH was studied in 14 normal subjects. A statistically significant reduction of urinary pH was recorded with ammonium chloride in daily doses of 1.5 and 3 g, but not with 2g of methenamine hippurate or 1.8 g of ascorbic acid. Long-term treatment with ammonium chloride in doses between 1.5 and 3 g was given to 11 patients in order to reduce the risk of new stone formation or growth of fragments remaining after disintegration of infected renal stones. Biochemical stone analyses showed struvite in 9 of the treated stones, and urine cultures verified the presence of urease-producing bacteria in 10 patients. Apart from ammonium chloride, the patients were treated with antibiotics, in 4 patients continuously and in the others during periods from 2 to 34 months. The patients were followed for an average period of 32 months. No adverse reactions were recorded with the dosage used. Initially, 6 patients were stone-free, whereas 5 had residual stone fragments with a largest diameter ranging from 4 to 20 mm. At follow-up, 2 patients were still stone-free, and of 5 patients with residual fragments 1 showed stable disease and 3 an improved stone situation. In 5 patients, 3 of whom had residual stone fragments, antibiotic treatment had been interrupted without infectious relapse. Our conclusion is that long-term urinary acidification is possible despite residual fragments and that it might be a beneficial therapeutic supplement to patients who have been treated for infected renal stones, particularly if disintegrated stone material resides in the kidney following extracorporeal or percutaneous lithotripsy procedures.
The crystallization of magnesium ammonium phosphate (MAP) was studied in salt solutions and dialysed urine at similar levels of MAP supersaturation. At pH levels of 7.1 or higher crystallization occurred to the same extent in solutions with and without urinary macromolecules. Whereas crystals in the size range 3.5-5 microns were observed in the salt solution at pH 7.0, this was not so in dialysed urine. When the crystal size distribution was determined after 30 min larger crystals were observed in dialysed urine, indicating a promoting effect by urinary macromolecules on the formation of MAP crystals. A modified AP(MAP) index was formulated based on calculations with the EQUIL 2 programme in order to improve the relationship between this simplified estimate and the ion-activity product of MAP (APMAP). This index had the following form: [formula: see text] for 24-h values of magnesium (Mg), ammonium (NH4), phosphate (P), pH and urine volume (V). The APMAP required for the formation of 2,000 crystals in the size range 3.5-5 microns varied between 226 x 10(-15) and 293 x 10(-15) (mmol/l)2 in dialysed urine. An experimental system was designed based on the measurement of pH during the addition of NH4OH. At the point assumed to correspond to the start of crystallization, AP(MAP) index values between 409 and 903 were recorded. Such a test might provide useful information on the crystallization properties in urine.
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