Hydrochlorothiazide Effects on Serum Calcium and Immunoreactive Parathyroid Hormone Concentrations

Abstract

Nine normal subjects were given 50 mg of hydrochlorothiazide twice daily for 25 days, to investigate the relationships between circulating immunoreactive parathyroid hormone (iPTH) and changes in calcium homeostasis induced by this diuretic. Total and ionized plasma calcium concentrations were significantly increased during administration of hydrochlorothiazide and for at least 2 weeks after withdrawal of the drug. There was no clearly definable effect either on protein binding of calcium or on iPTH. The normal negative correlation between ionized calcium and iPTH appeared to remain intact, and the mechanism of the increase in serum calcium is yet to be elucidated.