Effect of amiloride with or without hydrochlorothiazide on urinary calcium and saturation of calcium salts

To assess the therapeutic role of amiloride in calcium nephrolithiasis, seven patients with renal stones were evaluated before and after 1 month of treatment each with amiloride (2.5 mg twice daily), hydrochlorothiazide (25 mg, twice daily), and both drugs at the same dosages. Although amiloride alone reduced urinary calcium in only two patients, it caused a slightly more prominent decline in urinary calcium when added to hydrochlorothiazide treatment in five patients. The urinary saturation of stone-forming salts (brushite and calcium oxalate) decreased significantly during treatment with hydrochlorothiazide alone or in combination with amiloride. Although the decrease in brushite saturation was slightly more marked with the combined treatment, the reduction in calcium oxalate saturation was equivalent during the two treatment phases. Although serum potassium was significantly reduced during combined treatment with amiloride and hydrochlorothiazide, this reduction was not as prominent as that occurring during treatment with hydrochlorothiazide alone. The results suggest that the addition of amiloride to hydrochlorothiazide treatment in calcium nephrolithiasis may be advantageous, because of its stimulation, though slight, of the thiazide-induced reduction of urinary calcium and saturation of calcium phosphate and because it may avert the development of severe hypokalemia.