HYPOMAGNESEMIA
If unsure, the distinction between gastrointestinal losses
and renal losses can be made by measuring the 24-hour urinary magnesium
excretion. In addition, one can calculate the fractional excretion of magnesium
(on a random urine specimen) with the following formula where U and P refer to
the urine and plasma concentrations of magnesium (Mg) and creatinine (Cr).
FEMg = [(UMg x PCr) /
(PMg x UCr x 0.7)] x 100
If the fractional excretion of magnesium is above 2% in
someone with normal renal function, the hypomagnesemia is likely secondary to
renal magnesium wasting from drugs such as diuretics, aminoglycosides, or
cisplatin.
2 grams of IV magnesium sulfate increased serum levels by a paltry median of 0.2 mg/dL.
Rechecking
too soon may give a false sense of security.
- If the Magnesium level is 1.7 to 2, give 2 grams of MgSO4 IV.
- If the Magnesium level is 1.3 to 1.7 give 4 grams of MgSO4 IV.
Parenteral (IV or IM): Magnesium Sulfate (MgSO4)
Magnesium Sulfate is 10% elemental (1 gram of Magnesium per
100 ml solution)
- One gram of MgSO4 contains 8.12 meq of Magnesium
- One ml MgSO4 50% Solution = 4 meq Magnesium
- One ml MgSO4 10% Solution = 0.8 meq Magnesium
Satyendra Dhar MD,
