MgCaCO 3 Versus CaCO 3 in Peritoneal Dialysis Patients – a Cross-over Pilot Trial

Background Despite adverse effects such as constipation, vascular calcification, and hypercalcemia, calcium-based salts are relatively affordable and effective phosphate binders that remain in widespread use in the dialysis population. We conducted a pilot study examining whether the use of a combined magnesium/calcium-based binder was as effective as calcium carbonate at lowering serum phosphate levels in peritoneal dialysis (PD) patients.Methods This was a cross-over, investigator-masked pilot study in which prevalent PD patients received calcium carbonate alone (200 mg calcium per tablet) or calcium magnesium carbonate (100 mg calcium, 85 mg magnesium per tablet). Primary outcome was serum phosphate level at 3 months. Analysis was as per protocol.Results Twenty patients were recruited, 17 completed the study. Mean starting dose was 11.35 ± 7.04 pills per day of MgCaCO 3 and 9.00 ± 4.97 pills per day of CaCO 3 . Mean phosphate levels fell from 2.13 mmol/L to 2.01 mmol/L (95% confidence interval (CI): 1.76 – 2.30, p = 0.361) in the MgCaCO 3 group, and 1.81 mmol/L (95% CI: 1.56 – 2.0, p = 0.026) in the CaCO 3 alone group. Six (35%) patients taking MgCaCO 3 and 9 (54%) taking CaCO 3 alone achieved Kidney Disease Outcomes Quality Initiative (KDOQI) serum phosphate targets at 3 months. Diarrhea developed in 9 patients taking MgCaCO 3 and 3 taking CaCO 3 . Serum magnesium exceeded 1.4 mmol/L in 5 patients taking MgCaCO 3 while serum calcium exceeded 2.65 mmol/L in 3 patients receiving CaCO 3 . When compared to the initial dose, the prescribed dose at 3 months was reduced by 44% (to 6.41 tablets/day) in the MgCaCO 3 group and by 8% (to 8.24 pills per day) in the CaCO 3 alone group.Conclusion Compared with CaCO 3 alone, the preparation and dose of MgCaCO 3 used in this pilot study was no better at lowering serum phosphate levels in PD patients, and was associated with more dose-limiting side effects.