Long-Term (6 Months) Cross-Over Comparison of Calcium Acetate with Calcium Carbonate as Phosphate Binder

Abstract

A previous short-term study of 10 weeks in 8 patients had shown us that with half the dose of elemental calcium, calcium acetate (CaAc) could control predialysis plasma phosphate (PPO₄) as well as calcium carbonate (CaCO₃) but that the incidence of hypercalcemia was not decreased. To better appreciate the value of CaAc in comparison to CaCO₃, CaAc was given to 28 patients on chronic hemodialysis (6 men, 22 women, age 61 ± 14 years; dialyzate Ca: 1.5 mmol/l) for 6 months to replace CaCO₃ at half the dose of elemental calcium (1,235 ± 521 versus 2,375 ± 1,470 mg/day). Because of gastrointestinal intolerance, CaAc had to be discontinued in 5 patients after 1-5 months. Magnesium hydroxide [Mg(OH)₂] given in 18 of them in association with CaCO₃ was discontinued and reintroduced in 6 patients in order to keep PPO₄ < 2 mmol/l. Mean dosage of Mg(OH)₂ was 2.09 ± 1.4 g/day with CaCO₃ and 0.9 ± 0.5 with CaAc. Predialysis plasma concentrations of calcium and phosphate were monitored weekly during the 3 months of the control period under CaCO₃ and during the 6-month administration of CaAc. Plasma calcium (PCa) was comparable with the 2 treatments (2.47 ± 0.11 vs. 2.5 ± 0.10 mmol/l), but PPO₄ was significantly lower with CaAc (1.82 ± 0.26 vs. 1.73 ± 0.23 mmol/l). Plasma alkaline phosphatase remained constant (122 ± 66 vs. 122 ± 70; normal < 170 UI/l) as well as plasma intact PTH (121 ± 153 vs. 121 ± 146; normal < 54 pg/ml) and plasma aluminum (0.34 ± 0.23 vs. 0.32 ± 0.20 μmol/l). Hypercalcemia (PCa > 2.7 mmol/l) was present in 11 patients with CaCO₃ and in 16 patients with CaAc, and its incidence did not decrease with CaAc (8.2 vs. 8%). In conclusion, this long-term study confirms that CaAc is a more efficient PO₄binder than CaCO₃. However, its gastrointestinal tolerance seems poorer and the incidence of hypercalcemia is not decreased. The paradox of the unchanged incidence of hypercalcemia with acetate in spite of a reduction by half of the amount of calcium ingested may have two explanations: the very presence of a lower plasma PO₄ concentration (by a physicochemical mechanism) and the possible greater bioavailability of the calcium for absorption when it is given as CaAc.