Possible benefit in using magnesium carbonate as a phosphate binder in hemodialysis patients.


ORLANDO—A small pilot study suggests that magnesium may prevent or delay progression of vascular calcification in hemodialysis patients without a detrimental effect on bone, researchers reported here at the 2008 Annual Dialysis Conference.

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Magnesium has not been adequately studied in dialysis patients, notes lead investigator David M. Spiegel, MD, professor of medicine at the University of Colorado Health Sciences Center in Denver. The general consensus, he says, is that magnesium should be avoided in dialysis patients to prevent hypermagnesemia and that magnesium binders result in diarrhea.


In a previous study, he and colleagues demonstrated that a combination binder of magnesium carbonate and calcium carbonate is an effective phosphate bind and is well tolerated in dialysis patients. Two observational studies in hemodialysis patients showed decreased vascular calcification in patients with higher serum magnesium concentrations and in vitro studies have shown that magnesium inhibits hydroxyapatite crystal growth.


Dr. Spiegel’s group hypothesized that magnesium, through its ability to combine with calcium and phosphorus, might inhibit vascular calcification but could impair normal bone formation.

Their study looked at seven hemodiaysis patients (five men, two women) with baseline coronary artery calcification (CAC) scores higher than 30. Baseline scores ranged from 139 to 6,943. All patients stopped taking their binder and started on magnesium carbonate/calcium carbonate binder (magnesium 86 mg/pill and calcium 100 mg/pill). Patients could receive vitamin D analogues but not cinacalcet.


All patients dialyzed on a 2.5 mEq/L Ca and a 0.75 mEq/L Mg dialysate. Magnesium binders were increased if the phosphorus level was greater than 5.5 mg/dL. Magnesium supplements were prescribed if the serum magnesium was less than 2.67 mEq/L (3.2 mg/dL) unless the patient was having side effects. Electron beam tomography scans were performed at baseline, six, 12, and 18 months for CAC scores and vertebral bone mineral density (BMD).


Over the 18 months, the researchers observed no significant change in CAC score measured as median percent change (8%, 3.9%, and 8.0% increase at six, 12, and 18 months) and a small but nonsignificant decrease in vertebral BMD (mean 156 g/cm2 at baseline to 137 g/cm2 at 18 months.)


When used as the principal phosphate binder for 18 months, Dr. Spiegel concluded, magnesium carbonate/calcium carbonate provided excellent control of serum phosphorus, prevented progression of vascular calcification and did not worsen BMD.