Long-term effects of calcium carbonate and 2.5 mEq/liter calcium dialysate on mineral metabolism

Abstract

Many investigators have shown that calcium carbonate (CaCO3) is an effective phosphate binder which also prevents the potential disabling effects of aluminum (Al) accumulation. However, hypercalcemia may develop in a substantial number of patients. Thus, to control serum phosphate (PO4) and prevent hypercalcemia, we performed studies in 21 patients on maintenance hemodialysis in which, in addition to the oral administration of CaCO3, the concentration of calcium (Ca) in the dialysate was reduced from 3.25 to 2.5 mEq/liter. The studies were divided in three periods: I. control, on Al-binders (one month); II. no Al-binders (one month); III. CaCO3 (seven months). Blood was obtained three times/week before dialysis for the first five months of the study and once a week for the remaining four months. During the control period, the mean serum calcium was 8.86 ± 0.08 mg/dl. The value decreased to 8.65 ± 0.07 mg/dl when phosphate binders containing aluminum were discontinued, and increased to 9.19 ± 0.07 mg/dl (P < 0.001 compared to period II) during oral supplementation with calcium carbonate. The mean serum phosphorus was 5.03 ± 0.07 mg/dl during the control period, and increased to 7.29 ± 0.91 mg/dl (P < 0.001) after phosphate binders were discontinued. It decreased to 4.95 ± 0.06 mg/dl (P < 0.001) with the administration of calcium carbonate. During CaCO3 administration, serum Al decreased from 64.2 ± 8.5 to 37.1 ± 3.6 and 25.1 ± 3.0 μg/liter (P < 0.001) at three and seven months, respectively. Serum parathyroid hormone (PTH) decreased by 20%. In summary, lowering dialysate Ca to 2.5 mEq/liter allowed the long-term administration of large doses of CaCO3 (10.5 g/day). This corrected the hyperphosphatemia without the development of hypercalcemia or worsening of the secondary hyperparathyroidism. Al levels returned toward normal. Thus, by utilizing this maneuver aluminum binders may be unnecessary in the majority of patients on maintenance hemodialysis.