RENAL MAGNESIUM WASTING ASSOCIATED WITH AMPHOTERICIN-B THERAPY

The effect of amphotericin B on Mg metabolism was studied in 10 patients (aged 30-68 yr) with systemic fungal infections. Renal Mg wasting resulting in mild to moderate hypomagnesemia was demonstrated by the 2nd wk of therapy following relatively small cumulative dosages of amphotericin B (208 .+-. 40 mg). The lowest serum levels and largest fractional excretions of Mg were observed by the 4th wk of therapy after cumulative dosages of 510 .+-. 118 mg. A plateauing of the renal Mg wasting is suggested, as there were no further increases or reductions in fractional Mg excretion and serum Mg level, respectively, despite continued amphotericin B administration. Reversibility of the Mg wasting is indicated by data in 3 of the patients .apprx. 1 yr following discontinuation of amphotericin B therapy, in whom the serum Mg level and fractional Mg excretion had returned to pretreatment baseline values. Although the available data do not allow precise localization of this defect, increased urinary excretion of Mg despite its reduced filtered load suggests a tubular defect in Mg reabsorption. Routine monitoring of the serum Mg level during treatment with amphotericin B is recommended.