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

Abstract

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 MgCaCO₃ and 9.00 ± 4.97 pills per day of CaCO₃. 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 MgCaCO₃ group, and 1.81 mmol/L (95% CI: 1.56 – 2.0, p = 0.026) in the CaCO₃ alone group. Six (35%) patients taking MgCaCO₃ and 9 (54%) taking CaCO₃ alone achieved Kidney Disease Outcomes Quality Initiative (KDOQI) serum phosphate targets at 3 months. Diarrhea developed in 9 patients taking MgCaCO₃ and 3 taking CaCO₃. Serum magnesium exceeded 1.4 mmol/L in 5 patients taking MgCaCO₃ while serum calcium exceeded 2.65 mmol/L in 3 patients receiving CaCO₃. When compared to the initial dose, the prescribed dose at 3 months was reduced by 44% (to 6.41 tablets/day) in the MgCaCO₃ group and by 8% (to 8.24 pills per day) in the CaCO₃ alone group.

Conclusion

Compared with CaCO₃ alone, the preparation and dose of MgCaCO₃ 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.