Magnesium sulfate injection is available as a 50% (500 mg/mL) solution in 2-, 10-, 20-, and 50-mL single-use vials.3811; 3812 Each mL of solution contains 500 mg of magnesium sulfate heptahydrate (equivalent to 4.06 mEq/mL of magnesium) in water for injection.3811 Vials may also contain sulfuric acid and/or sodium hydroxide for pH adjustment.3811
Magnesium sulfate also is available as a premixed infusion solution at concentrations of 4 or 8% in water for injection and 1% in dextrose 5% in single-use flexible plastic containers.3813; 3814 The 4% solution contains 40 mg/mL of magnesium sulfate heptahydrate (equivalent to 0.325 mEq/mL of magnesium) and the 8% solution contains 80 mg/mL of magnesium sulfate heptahydrate (equivalent to 0.65 mEq/mL of magnesium) in water for injection.3813 The 1% solution contains 10 mg/mL of magnesium sulfate heptahydrate (equivalent to 0.081 mEq/mL of magnesium) and dextrose anhydrous 5 mg/mL in water for injection.3814 The premixed infusion solutions may contain sulfuric acid and/or sodium hydroxide for pH adjustment.3813; 3814
pH
The pH of a 5% solution ranges from 5.5 to 7.3811
The premixed infusion solutions have pH values in the range of 3.5 to 6.5.3813; 3814
Osmolarity
The 50% solution has a calculated osmolarity of 4060 mOsm/L.3811
The premixed 4 and 8% solutions in water for injection have calculated osmolarities of 325 and 649 mOsm/L, respectively.3813 The premixed 1% solution in dextrose 5% has a calculated osmolarity of 333 mOsm/L.3814
Magnesium sulfate may be administered by intramuscular or direct intravenous injection and by continuous or intermittent intravenous infusion.3811 Premixed infusion solutions are administered by intravenous infusion only.3813; 3814 For intravenous injection, magnesium sulfate must be diluted to a concentration of 20% or less; the rate of injection generally should not exceed 150 mg (e.g., 1.5 mL of a 10% solution or 3.75 mL of a 4% solution) per minute, unless more rapid administration is indicated.3811; 3813 For the treatment of hypomagnesemia, the manufacturer states that 5 g (approximately 40 mEq) of magnesium sulfate can be added to 1 L of dextrose 5% or sodium chloride 9% for slow intravenous infusion over 3 hours.3811 For intramuscular injection, magnesium sulfate 50% injection may be administered undiluted in adults but should be diluted to 20% or less for infants and children.3811
Intact vials of magnesium sulfate 50% injection and premixed infusion solutions should be stored at controlled room temperature and protected from freezing.3811; 3813; 3814 It has been reported that refrigeration of magnesium sulfate injection may result in precipitation or crystallization.593
Standardize 4 Safety
One or more standardized concentrations for this drug have been established through Standardize 4 Safety (S4S), a national patient safety initiative to reduce medication errors, especially during transitions of care. (See Standardize 4 Safety in Users Guide.) Recommendations developed to date through this initiative are available at www.ashp.org/pharmacy-practice/standardize-4-safety-initiative.
Table 1: Standardize 4 Safety Continuous IV Infusion Standard Concentrations for Magnesium Sulfate3636
| Patient Population | Concentration Standards | Dosing Units |
|---|---|---|
| Adultsa | 40 mg/mL | grams (note dosing units differ from concentration units) |
a See ISMP for best practices. https://www.ismp.org/resources/taking-closer-look-medication-errors-involve-oxytocin; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3956395/
Drugs in Syringe Compatibility
Y-Site Injection Compatibility (1:1 Mixture)
Additional Compatibility Information
Manufacturers state that magnesium sulfate is potentially incompatible with and may result in precipitate formation when mixed with solutions containing alcohol, alkali carbonates and bicarbonates, alkali hydroxides, arsenates, barium, calcium, clindamycin phosphate, heavy metals, hydrocortisone sodium succinate, phosphates, polymyxin B sulfate, procaine hydrochloride, salicylates, strontium, or tartrates.3811 These potential incompatibilities may be dependent on concentration and solution pH.3811
For a list of references cited in the text of this monograph, search the monograph titled References.