Background. The calcineurin inhibitors, cyclosporine A (CSA) and tacrolimus, cause hypomagnesemia by suppressing reabsorption of magnesium (Mg) from renal tubules. To assess whether the effect on Mg metabolism after allogeneic hematopoietic stem cell transplantation (HSCT) differs among calcineurin inhibitors, we prospectively evaluated the Mg metabolism in recipients of allogeneic HSCT who received CSA or tacrolimus Methods. Patients who underwent allogeneic HSCT were enrolled. CSA and tacrolimus were given by continuous infusion starting from day -1. Serum Mg and the total amount of urinary Mg excretion were measured once before starting of CSA or tacrolimus, and once weekly after HSCT for 4 weeks. Mg was supplemented with magnesium 1-aspartate by continuous infusion to maintain the serum Mg level > 1.4 mEq/L. Results. Thirty-six patients were evaluated (12 in the CSA group, 24 in the tacrolimus group). The serum Mg level began to decrease in both groups at the first week after HSCT, and the mean serum Mg levels were significantly lower in the tacrolimus group than in the CSA group from the first to the third week. The total amount of urinary Mg excretion and Mg supplementation began to increase in both groups at the second week after HSCT, and the amounts in the tacrolimus group were significantly higher than those in the CSA group. Conclusions. Although both calcineurin inhibitors increased urinary Mg excretion and caused hypomagnesemia shortly after HSCT, the effect was more significant with tacrolimus than with CSA. This observation may explain the higher incidence of renal impairment and encephalopathy in patients receiving tacrolimus.
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