Profound hypomagnesemia and renal magnesium wasting associated with the use of cyclosporine for marrow transplantation.

We prospectively studied 41 marrow transplant patients to evaluate the possible association of hypomagnesemia with cyclosporine immunosuppressive therapy. During the 3 months posttransplant the mean nadir serum magnesium level was 1.06 +/- 0.16 mEq/L in 24 patients treated with cyclosporine and 1.33 +/- 0.13 in 14 patients treated with methotrexate (P less than 0.0001). Eleven of 24 patients receiving cyclosporine versus 1 of 14 patients receiving methotrexate had magnesium levels less than 1 mEq/L, or were begun on replacement therapy for presumed symptomatic hypomagnesemia (P less than 0.02). Agents known to be associated with hypomagnesemia, aminoglycosides and amphotericin B, were given in both lesser quantity and frequency to cyclosporine-treated patients than to methotrexate-treated patients. Hypomagnesemic patients treated with cyclosporine had inappropriately elevated urine magnesium excretion. Renal magnesium wasting may be added to the spectrum of nephrotoxicity resulting from cyclosporine. Several adverse reactions previously attributed to cyclosporine may be secondary to magnesium deficiency.