Effects of cimetidine on parathyroid hormone in chronic uremia.

Recent case reports suggest suppression of immunoreactive parathyroid hormone (iPTH) with cimetidine in two patients with primary hyperparathyroidism. In both patients peptic ulcer disease led to medical treatment with cimetidine. In the first patient given oral cimetidine (800 mg then 400 mg daily) for 8 months, iPTH decreased from 20 times to 6 times normal1. No changes in serum calcium and phosphorus occurred, but inhibition of gastric acid secretion and ulcer healing were demonstrated. In the second patient, a woman with a parathyoid adenoma, cimetidine treatment (1200 mg daily) was associated with a decrease in iPTH levels from a value 2.5 times normal to a normal value2,3. Concommittantly, serum calcium decreased from 11.3 mg/dl to 10.3 mg/dl and serum phosphorus increased from 2.1 mg/dl to 2.7 mg/dl. One month after discontinuation of cimetidine therapy iPTH had rebounded to values thrice normal and serum calcium and phosphorus were 10.8 and 2.3 mg/dl, respectively.