Calcium Carbonate as Phosphate Binder in Patients on Low-Calcium Dialysate

Robert L. Lins, MD, Department of Nephrology and Hypertension A.Z. Stuivenberg, Lange Beeldekensstraat 267, B-2008 Antwerp (Belgium) In a recent editorial about the treatment of uremic hyperphosphatemia, Schaefer et al. [1] wondered if calcium-free dialysate could reduce the potential risks of therapy with CaC03. Although no published studies about the use of calcium-free dialysate exist, there are some reports about using low-calcium dialysate (LCD) [2–4]. Mactier et al. [2] concluded that in most hemodialysis patients CaC03 could effectively prevent hyperphosphatemia without the risk of hypercalcemia, using LCD. Our results of a prospective study [3, 4], using LCD (2,5 mEq/1) in 7 patients who previously developed hypercalcemia when regular calcium dialysate (RCD; 3.75 mEq/ 1) was used, differ somewhat from those of Mactier. Although the intake of Al(OH)3 could be significantly decreased and that of CaC03 increased, the average cal-cemia, number of hypercalcemic episodes and control of serum phosphate were not significantly different comparing RCD and LCD periods. Moreover, the dose to control phosphatemia was 3 times higher for CaC03 than for Al(OH)3, resulting in poor patient compliance. While increasing the dose of CaCC > 3, considerable fluctuations of serum phosphate and calcium were seen, necessitating frequent serum determinations. In our own (3 months) as well as in the study by Mactier et al., the follow-up period might have been too short. Sometimes there was a delay of several weeks between changing CaC03 intake and stabilization of serum calcium levels. We are aware that factors like vitamin D intake, parathyroid and aluminum burden will considerably influence the results. Therefore we believe that our own results and those of Mactier et al., suggest that probably a subgroup of patients will benefit from CaCC > 3 as a phosphate binder using low-calcium or even calcium-free dialysate. Long-term studies with a greater number of patients have to be done to confirm this. References Schaefer K, von Herrath D, Myrthe Erley CM: Treatment of uremic hyperphosphatemia. Is there still a need for aluminum salts? Am J Nephrol 1988;8:173–178.