What factors should be taken into account when determining magnesium repletion doses to treat hypomagnesemia?

Updated: Oct 30, 2020
  • Author: Tibor Fulop, MD, PhD, FACP, FASN; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

The route of magnesium repletion varies with the severity of the clinical manifestations. For example, the hypocalcemic-hypomagnesemic patient with tetany or the patient who is suspected of having hypomagnesemic-hypokalemic ventricular arrhythmias should receive 50 mEq of intravenous magnesium, given slowly over 8-24 hours. This dose can be repeated as necessary to maintain the plasma magnesium concentration above 1.0 mg/dL (0.4 mmol/L or 0.8 mEq/L). In the normomagnesemic patient with hypocalcemia, it has been suggested that this dose be repeated daily for 3-5 days.

It must be appreciated that the plasma magnesium concentration is the major regulator of magnesium reabsorption in the loop of Henle, the major site of active magnesium transport. Thus, an abrupt elevation in the plasma magnesium concentration will partially remove the stimulus for magnesium retention, and up to 50% of the infused magnesium will be excreted in the urine.

Furthermore, because magnesium is subject to slow equilibration between serum and the intracellular spaces and tissues (eg, bone, red blood cells, muscle), the serum magnesium level may appear artificially high if measured too soon after a magnesium dose is administered. Significant magnesium depletion requires sustained correction of the hypomagnesemia.


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