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

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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 PO4 binder 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.

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