Additive hypocalciuric effects of amiloride and hydrochlorothiazide in patients treated with calcitriol.

To compare the effects of hydrochlorothiazide (HCTZ) alone and in combination with amiloride on urinary calcium excretion we performed 14 acute studies on 7 patients with vitamin-D-induced calciuria. Each patient was studied first with HCTZ alone, and 1-32 weeks later with the same or lower dose of HCTZ combined with amiloride. Administration of HCTZ alone did not change UCaV during the 1st day of therapy, and caused a significant reduction from 44.4 +/- 28.8 to 26.0 +/- 14.4 mg/m2/24 h (p less than 0.02) on the 4th day. In contrast, combined diuretic regimen caused a significant reduction in UCaV from 36.0 +/- 16.7 to 23.6 +/- 14.4 mg/m2/24 h (p less than 0.02) on the 1st day and further reduction to 13.3 +/- 6.9 mg/m2/24 h (p less than 0.01) on the 4th day. UCaV on the 4th day was significantly lower with the HCTZ-amiloride combination (p less than 0.05). The combined therapy caused a greater reduction in FECa/FENa than HCTZ alone on the 1st day (p less than 0.02) and on the 4th day (p less than 0.01). HCTZ-induced hyperkaluria, hypokalemia and alkalosis were prevented by the addition of amiloride. In another patient, low-dose HCTZ-amiloride had a maximal dissociative effect on FECa/FENa and was more effective than HCTZ given alone in a double dose. 3 patients were treated with the low-dose HCTZ-amiloride regimen for a total of 23 months. UCaV was kept persistently low.(ABSTRACT TRUNCATED AT 250 WORDS)