Tacrolimus-Associated Hypomagnesemia in Renal Transplant Recipients

Abstract

Background Since hypomagnesemia occurs frequently in tacrolimus treated patients, we studied the correlation between renal magnesium wasting and tacrolimus blood levels in renal transplant patients. Methods Serum magnesium, fractional excretion of magnesium (FE Mg), and 24-hour urinary excretion of magnesium were measured in 41 transplant patients and 10 healthy volunteers for correlation with tacrolimus level. Results Of tacrolimus-treated patients, 43% displayed hypomagnesemia. FE Mg (7.42 ± 3.59% versus 1.88 ± 0.43%) and 24-hour urinary excretion (112.36 ± 51.43 mg/dL versus 6.7 ± 2.79 mg/dL) were significantly higher among tacrolimus-treated patients than controls. Magnesium replacement did not influence FE Mg or 24-hour urinary magnesium excretion. Tacrolimus level was the best predictor of 24-hour urinary magnesium excretion and FE Mg. Serum magnesium levels correlated inversely with tacrolimus concentrations and creatinine clearance. Conclusion Hypomagnesemia in renal transplant recipients results from renal magnesium wasting. Tacrolimus levels and renal function impact on the excess renal magnesium excretion. Studies of longer duration are warranted to assess the long-term effects of this early posttransplant hypomagnesemia.