Effect of cimetidine on serum carboxyl and aminoterminal fragments of parathyroid hormone in chronic uraemic patients.

The effect of cimetidine on abnormally elevated serum levels of parathyroid hormone was studied in 21 patients with secondary hyperparathyroidism due to chronic renal failure, receiving regular dialysis treatment. The concentrations of carboxyl (-COOH) and aminoterminal (-NH2) fragments of circulating immunoreactive parathyroid hormone (iPTH) were determined before and after 2 months af treatment with cimetidine 400 mg/day. All patients had, on admission, raised levels of either hormonal fragment. The mean pre-treatment value was 17.2 mU/ml for -COOH terminus (upper normal limit 6.5 mU/ml) and 5.7 mU/ml for -NH2 terminus (upper normal limit 1.9 mU/ml). At the end of cimetidine treatment the mean values were 19.9 and 5.7 mU/ml respectively for the two forms of circulating iPTH. No changes in total serum calcium, phosphate or alkaline phosphatase activity were recorded during the study. These results do not indicate any lowering effect of cimetidine on serum iPTH in chronic uraemic patients with secondary hyperparathyroidism.