MgCaCO3 versus CaCO3 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.

Keywords: Phosphate-binders; adverse effects; compliance rates; magnesium calcium carbonate.

Figure 1 —

Study Schema. * Inclusion criteria: prevalent peritoneal dialysis (PD) patients, age >18 years, PO₄ >1.80 mmol/L on 2 occasions, CaCO₃ was the only PO₄ binder. ** At enrollment all patients were taking a CaCO₃ preparation containing 500 mg elemental calcium per tablet. This was converted to a Tums (GlaxoSmithKline Inc., Mississauga, ON, Canada) equivalent (either Tums with 200 mg elemental calcium per tablet or Magnebind 300 (Nephro-Tech, Inc., Shawnee, KS, USA) with 85 mg elemental magnesium and 100 mg elemental calcium per tablet).

Figure 2 —

Mean serum phosphate, calcium, and magnesium concentrations at 0, 6 and 12 weeks. Tums (GlaxoSmithKline, Mississauga, ON, Canada).