Magnesium balance and distribution during total parenteral nutrition: effect of calcium additives

Homeostatic alterations and derangements in magnesium (and phosphate) metabolism may occur during total parenteral nutrition (TPN) and may be influenced by the amounts of calcium supplied daily. We tested these possibilities in previously fasted or nonfasted animals receiving TPN with variable amounts of calcium. Large calcium additives (90 mg/d) produced hypomagnesemia in nonfasted animals and increased the degree of hypomagnesemia observed in some of the fasted groups. Bone and muscle magnesium were occasionally altered, by high-calcium additives. Urine magnesium was increased, metabolism may have been dependent upon the amount of calcium added and magnesium supplied in TPN. Some of the derangements may have been dependent upon the state of fasting (and resultant phosphate-depletion syndrome).