High-dose calcium carbonate with stepwise reduction in dialysate calcium concentration: effective phosphate control and aluminium avoidance in haemodialysis patients.

To reduce potentially toxic aluminium exposure, the phosphate binding agent aluminium hydroxide was replaced by high-dose oral calcium carbonate in 15 haemodialysis patients. Stepwise reduction in dialysate calcium concentration (from 1.75 to 1.35 mmol/l and then to 1.05 mmol/l) was made when necessitated by hypercalcaemia. After 6 months, the mean daily dose of calcium carbonate was 62 mmol (range 25-150 mmol). This dose maintained good control of plasma phosphate (baseline, 1.34 +/- 0.32 mmol/l (mean +/- SD); 12 weeks, 1.30 +/- 0.22 mmol/l; 24 weeks, 1.51 +/- 0.31 mmol/l). Calcium x phosphate product did not rise significantly (baseline, 3.41; 12 weeks, 3.44; 24 weeks, 4.02). Apart from a transient early increase, ionised calcium did not change significantly (baseline, 1.23 +/- 0.10 mmol/l; 12 weeks, 1.24 +/- 0.10 mmol/l). Intact (1-84) parathyroid hormone concentration decreased from 241 pg/ml to 116 pg/ml (median values, P less than 0.05) after 12 weeks. This simple and well-tolerated regimen almost completely eliminated oral aluminium exposure, effectively controlled plasma phosphate and calcium concentrations, and reduced hyperparathyroidism.