Magnesium carbonate for phosphate control in patients on hemodialysis. A randomized controlled trial

Magnesium salts bind dietary phosphorus, but their use in renal patients is limited due to their potential for causing side effects. The aim of this study was to evaluate the efficacy and safety of magnesium carbonate (MgCO₃) as a phosphate-binder in hemodialysis patients.

Forty-six stable hemodialysis patients were randomly allocated to receive either MgCO₃ (n = 25) or calcium carbonate (CaCO₃), (n = 21) for 6 months. The concentration of Mg in the dialysate bath was 0.30 mmol/l in the MgCO₃ group and 0.48 mmol/l in the CaCO₃ group.

Only two of 25 patients (8%) discontinued ingestion of MgCO₃ due to complications: one (4%) because of persistent diarrhea, and the other (4%) because of recurrent hypermagnesemia. In the MgCO₃ and CaCO₃ groups, respectively, time-averaged (months 1–6) serum concentrations were: phosphate (P), 5.47 vs. 5.29 mg/dl, P = ns; Ca, 9.13 vs. 9.60 mg/dl, P < 0.001; Ca × P product, 50.35 vs. 50.70 (mg/dl)², P = ns; Mg, 2.57 vs. 2.41 mg/dl, P = ns; intact parathyroid hormone (iPTH), 285 vs. 235 pg/ml, P < 0.01. At month 6, iPTH levels did not differ between groups: 251 vs. 212 pg/ml, P = ns. At month 6 the percentages of patients with serum levels of phosphate, Ca × P product and iPTH that fell within the Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines were similar in both groups, whereas more patients in the MgCO₃ group (17/23; 73.91%) than in the CaCO₃ group (5/20, 25%) had serum Ca levels that fell within these guidelines, with the difference being significant at P < 0.01.

Our study shows that MgCO₃ administered for a period of 6 months is an effective and inexpensive agent to control serum phosphate levels in hemodialysis patients. The administration of MgCO₃ in combination with a low dialysate Mg concentration avoids the risk of severe hypermagnesemia.