Failure of Cimetidine to Affect Calcium Homeostasis in Familial Primary Hyperparathyroidism (Multiple Endocrine Neoplasia, Type 1)*

Abstract
Recent reports that cimetidine, a blocker of histamine H2 receptors, lowered serum calcium and/or immunoreactive parathyroid hormone (PTH) concentrations in primary or secondary hyperparathyroidism prompted us to administer the drug (300 mg, orally, every 6 h) to two patients with hyperparathyroidism accompanying familial multiple endocrine neoplasia type 1. The patients were hypercalcemic (10.9–11.2 mg/ dl), hypophosphatemic (2.0–2.4 mg/dl), and hypercalciuric (≥410 mg//24 h), with elevated urinary cAMP and phosphate clearance and inappropriately high serum immunoreactive PTH levels. Multiple observations of these variables over 5 weeks of cimetidine treatment showed no systematic changes; in particular, serum and urinary calcium did not change, and there was no evidence of a decreased PTH effect on the kidneys. The data offer no support for the treatment of familial hyperparathyroidism with cimetidine.

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