Dissociation of calcium and sodium clearances in patients with hypoparathyroidism by infusion of chlorothiazide.

Previous reports have identified a deficient hypocalciuric response to chronic treatment with thiazide diuretics in patients with hypoparathyroidism. The present study was designed to ascertain if the acute response to thiazide diuretics is impaired in hypoparathyroidism. Five normal subjects and five patients with hypoparathyroidism were studied with the renal clearance technique during water diuresis. In normal subjects the clearance of calcium/clearance of sodium was 0.98 +/- 0.14 before, and 0.33 +/-0.03 during the intravenous infusion of chlorothiazide. In patients with hypoparathyroidism the corresponding ratios were 1.69 +/- 0.27 and 0.57 +/- 0.10. In both groups the drug-induced fall in clearance was 65% of control. The concentration of chlorothiazide in plasma and its rate of excretion were comparable in both groups. It is concluded that the acute action of thiazides is not impaired in hypoparathyroidism.