Acute effects of calcium carbonate and citrate on secondary hyperparathyroidism in chronic renal failure.

Two grams of elemental calcium as carbonate or citrate were given after an overnight fast to 14 patients with advanced renal failure (serum creatinine 759 +/- 365 mumol/l, mean +/- SD). The suppressibility of their hyperparathyroidism was confirmed with a calcium infusion test. Both calcium citrate and carbonate increased significantly plasma ionized calcium (6.8 and 4.5%, respectively) and total calcium (9.3 and 6.0%), p less than 0.001. In the majority of the patients, calcium citrate but not carbonate increased plasma calcium sufficiently to induce the suppression of hyperparathyroidism. The decrease of plasma intact parathyroid hormone was 35.9 +/- 24.8% (mean +/- SD); p less than 0.001) after calcium citrate and 9.2 +/- 18.9% (mean +/- SD; NS) after calcium carbonate.