Calcium carbonate is an effective phosphate binder when dialysate calcium concentration is adjusted to control hypercalcemia

The efficacy of calcium carbonate (CaCO3) as a phosphate binder has been limited by its tendency to cause hypercalcemia. Since standard dialysate calcium concentrations (3.0-3.5 mEq/l) increase the risk of developing hypercalcemia with large doses of CaCO3 by inducing positive calcium balance during hemodialysis (HD), we compared control of hyperphosphatemia in 41 HD patients during 4 months each of aluminum hydroxide (Al(OH)3) and CaCO3 when the dialysate calcium concentration was lowered, as required, to maintain the predialysis serum calcium concentration within the normal range. Mean predialysis serum phosphorus and calcium concentrations were 5.0 +/- 0.2 mg/dl and 9.3 +/- 0.1 mg/dl, respectively, during 4 months CaCO3 (9.2 +/- 0.3 g/day) and 4.9 +/- 0.2 g/dl and 9.1 +/- 0.1 mg/dl during the previous 4 months Al(OH)3 therapy (2.9 +/- 0.2 g/day). Reducing the dialysate calcium concentration to below 3.0 mEq/l (mean 2.1 +/- 0.04) in the 11 patients who developed hypercalcemia on CaCO3 decreased serum calcium (-1.1 +/- 0.15 mg/dl) and ionized calcium (-0.3 +/- 0.04 mEq/l) during HD, enabled CaCO3 (8.8 +/- 0.4 g/day) to be continued, and maintained predialysis serum calcium and phosphorus at 10.4 +/- 0.1 mg/dl and 5.2 +/- 0.3 mg/dl, respectively. No improvement in acidosis or biochemical hyperparathyroidism was observed during CaCO3 therapy but serum aluminum was significantly decreased after CaCO3 (p less than 0.005). We conclude that CaCO3 prevents interdialytic hyperphosphatemia as effectively as Al(OH)3 without increasing the predialysis serum calcium x phosphorus product, provided serum calcium is maintained within the normal range by adjusting the dialysate calcium concentration.