From the FDA Drug Label
MAGNESIUM SULFATE INJECTION, USP 50% 1gram per 2mL (500mg per mL) The amount of elemental magnesium in magnesium sulfate can be calculated by knowing the molecular weight of magnesium sulfate (121.29 g/mol for MgSO4 * 7H2O, but 120.37 g/mol for anhydrous MgSO4) and the atomic weight of magnesium (24.305 g/mol).
- Molecular weight of anhydrous MgSO4: 120.37 g/mol
- Atomic weight of Mg: 24.305 g/mol
- Percentage of Mg in MgSO4: (24.305 / 120.37) * 100 = 20.19% Given 2 grams of magnesium sulfate, the amount of elemental magnesium is:
- 2 g * (20.19 / 100) = 0.4038 g or 403.8 mg of elemental magnesium. 1
From the Research
The amount of elemental magnesium in 2 grams of magnesium sulfate is approximately 0.2 grams or 200 milligrams. This calculation is based on the molecular composition of magnesium sulfate (MgSO4), where magnesium makes up about 10% of the compound's total weight. Magnesium sulfate has a molecular weight of approximately 120.4 g/mol, with magnesium contributing 24.3 g/mol to that total. This means that in any amount of magnesium sulfate, roughly one-tenth is elemental magnesium. When using magnesium sulfate as a supplement or medication, it's essential to understand this distinction because dosing recommendations typically refer to the total compound weight rather than the elemental magnesium content. The body can only utilize the elemental portion, so knowing the actual magnesium content helps ensure appropriate dosing for nutritional or therapeutic purposes 2, 3, 4, 5, 6.
Some key points to consider when using magnesium sulfate include:
- The importance of understanding the molecular composition of magnesium sulfate to accurately calculate the amount of elemental magnesium.
- The need to consider the total compound weight versus the elemental magnesium content when interpreting dosing recommendations.
- The potential for variability in clinical practice patterns regarding the use of magnesium sulfate for eclampsia prevention and treatment, as highlighted in studies such as 6.
- The importance of following international recommendations for the use of magnesium sulfate, as inconsistent regimens may be used in some regions 6.
In terms of the provided evidence, while studies such as 2, 3, 4, and 5 discuss the use of magnesium sulfate for pre-eclampsia and eclampsia, they do not directly address the calculation of elemental magnesium in magnesium sulfate. However, the calculation of elemental magnesium is based on the molecular composition of magnesium sulfate, which is a fundamental concept in chemistry and pharmacology. Therefore, the calculation of approximately 0.2 grams or 200 milligrams of elemental magnesium in 2 grams of magnesium sulfate is a straightforward application of this concept.