THE REQUIREMENT OF LOW-CALCIUM DIALYSATE IN PATIENTS ON CONTINUOUS AMBULATORY PERITONEAL-DIALYSIS RECEIVING CALCIUM-CARBONATE AS A PHOSPHATE BINDER

In the present study we investigated the requirement of low calcium dialysate in 35 patients on continuous ambulatory peritoneal dialysis (CAPD) receiving calcium carbonate as the sole phosphate binder over a 12-month period. Patients with corrected serum calcium greater-than-or-equal-to 2.85 mmol/L after switching to oral calcium carbonate were given 1 to 3 2-litre exchanges of 2.5 mEq/L calcium dialysate. Serum phosphate level dropped from the pretreatment value of 2.95 +/- 0.62 to a level of between 1.70 +/- 0.41 to 2.03 +/- 0.44 mmol/L 2 weeks after therapy. Corrected serum calcium level increased significantly from 2 weeks onwards. Serum alkaline phosphatase rose initially at 2 and 6 weeks and decreased from 3 months onwards. Serum parathyroid hormone level dropped significantly from a mean pretreatment level of 569 to 320 pg/ml after 12 months (p <0.001). Serum aluminum decreased significantly from a mean of 1.04 to 0.65 umol/L (p <0.01). Daily calcium carbonate requirement fluctuated but tended to increase till 8 months and plateaued and ranged from 2.61 +/- 0.57 to 3.98 +/- 2.11 gm. The daily requirement of low calcium dialysate followed a similar trend with approximately three-quarters of patients ultimately requiring at least 1 bag of low calcium dialysate. Eight patients did not require low calcium dialysate. Patients who required low calcium dialysate were significantly older, had a significantly lower pretreatment serum parathyroid hormone and higher serum aluminum levels than those who did not. It was concluded that calcium carbonate is an effective phosphate binder in patients on CAPD and its use prevents aluminum accumulation in the body but the concomitant use of low calcium dialysate is required in the majority of patients receiving such treatment to prevent the development of hypercalcemia. This is especially so in patients with a lower degree of bone turnover.