Calcium Alginate versus Aluminum Hydroxide in Patients on Hemodialysis

Dr. D.C.H. Harris, Department of Renal Medicine, Westmead Hospital, Westmead, NSW 2145 (Australia) Dear Sir, Calcium alginate is a natural polyuronic acid charged with calcium which has been used successfully as a phosphate binder in patients on peritoneal [1] and hemodialysis [2, 3] in Germany. In addition to being aluminum-free, it has the potential advantage of causing less hypercalcemia than other calcium-containing phosphate binders. No other clinical studies of calcium alginate have been published, although another group reported it to be less effective than the initial studies suggested [4]. Therefore, we compared the efficacy of calcium alginate to that of aluminum hydroxide in patients on hospital hemodialysis. Seventeen patients (9 males), aged 56.3 ± 2.9 years and on hemodialysis in hospital for 4.1 ± 0.9 years, were enrolled in the study. There were 4 dropouts [due to death from ischemic heart disease (2), transplantation (1) and transfer to home hemodialysis (1)]. Twelve patients completed the study, and in another patient who died of ischemic heart disease, data are available from the first 2 months of each arm. Patients were randomized to receive aluminum hydroxide (‘Alutabs’, Riker Labs Aust., 600-mg tablet) for 6 months followed by calcium alginate (‘Phospholok’, Fisons Pty. Ltd., elemental Ca2+102 mg/g) in divided doses with meals (7 patients), or calcium alginate followed by aluminum hydroxide (6 patients). Dose was titrated each month to keep predialysis serum phosphate below 2 mmol/l (6.2 mg/dl) 3 days after the previous dialysis, to a maximum of 5.4 g [Al(OH)3] and 8.4 g (calcium alginate) per day. If phosphate was not controlled on maximum dose, Mylanta II [400 mg Al(OH)3, 400 mg Mg(OH)2 per tablet, Parke Davis Pty. Ltd.) was added. Magnesium aspartate (not with meals) was used to keep serum magnesium normal in patients not requiring Mylanta. Diet and dialysis time (4.2 ± 0.1 h 3 times per week) and dialysis calcium [1.5 mmol/l, (6 mg/dl)] were kept constant. No patients received vitamin D. For simplicity, and as results for each binder were not altered by the order of administration, data for each arm have been combined. Serum phosphate was not different between the 2 treatment arms after 4 months, but prior to this, during the period of dose titra-tion, it was significantly higher with calcium alginate (fig. 1). One patient developed hypercalcemia at 3 months while receiving calcium alginate (8.4 g/day), which persisted despite reduction of calcium alginate to 6 g/day [peak serum calcium 2.83 mmol/l (11.3 mg/dl)]. Otherwise, serum calcium was not different. Serum electrolytes, urea, creatinine, magnesium, alkaline phosphatase (measured monthly) and parathyroid hormone (whole molecule, RIA) were not different (table 1). Plasma aluminum was significantly higher during