Metolazone therapy of active calcium nephrolithiasis

Metolazone, a nonthiazide diuretic with the hypocalciuric effect of the thiazides, was evaluated in patients with idiopathic calcium nephrolithiasis. During the mean 3‐yr treatment period, there was a 77% decrease in stone incidence in 38 male patients (from 2.10 to 0.49 stones/patient/year). Urine calcium decreased 51% (from 231 ± 19 to 114 ± 7 mg/24 hr after 13 mo therapy). The treatment response was the same when these patients were divided into normocalciuric (n = 23), borderline hypercalciuric (n = 10), and hypercalciuric groups (n = 5). In six other patients with high sodium intake there was no decrease in urine calcium on metolazone, but hospitalization and sodium restriction restored the metolazone hypocalciuric effect. Metolazone is effective in reducing both calcium excretion and new stones in calcium stone formers regardless of the initial level of urine calcium excretion. High sodium intake may blunt and low intake potentiate the hypocalciuric effect of metolazone. Clinical Pharmacology and Therapeutics (1982) 32, 642–645; doi: 10.1038/clpt.1982.215