Furosemide-Induced Reduction in Ionized Calcium in Hypoparathyroid Patients

Abstract

Six hypoparathyroid patients were treated with oral furosemide for 4 days. All six had a significant decrease in serum ionized calcium level from the control period (4.05 ± 0.31 mg/dl) to the furosemide period (3.46 ± 0.26 mg/dl, P < 0.005). In five patients, the decrease in serum ionized calcium concentration occurred in association with an increase in urinary calcium excretion. Although serum immunoreactive parathyroid hormone level increased in five patients, it was insufficient to return serum ionized calcium to control levels. Changes in serum phosphorus, magnesium, or pH could not account for the observed decrease in serum ionized calcium concentration. It is necessary to monitor serum ionized calcium level in hypoparathyroid patients during furosemide therapy.