Diluting 2 Grams of Magnesium Sulfate by 20%
To dilute 2 grams of magnesium sulfate by 20%, you need to add 8 mL of normal saline to achieve a final volume of 50 mL.
Mathematical Calculation
The standard preparation described in multiple guidelines is 2 grams of magnesium sulfate in 50 mL of normal saline 1, 2. This represents the baseline concentration used for intravenous administration.
When diluting by 20%, you are reducing the concentration to 80% of the original:
- Original concentration: 2 grams in 50 mL = 40 mg/mL
- After 20% dilution: 2 grams in 62.5 mL = 32 mg/mL (which is 80% of original concentration)
- Therefore, add 12.5 mL of saline to the original 50 mL preparation
However, if starting with 2 grams of dry powder magnesium sulfate:
- To achieve a 20% dilution means creating a solution where the drug represents 20% concentration
- This requires adding saline to reach the appropriate final volume based on the desired concentration
Standard Clinical Preparations
The most commonly cited preparation across emergency and critical care guidelines is:
- 2 grams of magnesium sulfate diluted in 50 mL of normal saline 1, 2
- This is administered intravenously over 20-30 minutes for acute severe asthma 1, 2
- The same preparation (2 grams in 50 mL) is used for torsades de pointes 1, 2
Clinical Context Matters
For acute severe asthma in adults: 2 grams in 50 mL normal saline infused over 20 minutes is the standard dose 1, 2.
For pediatric patients: The dose is weight-based at 25-50 mg/kg (maximum 2 grams as a single dose) 1, which would require proportional dilution based on the calculated dose.
Important safety consideration: The concentration and infusion rate matter significantly—rapid administration can cause flushing, warmth, and hypotension 2, so the dilution volume affects both safety and efficacy of administration.