Magnesium sulfate has been on the World Health Organization’s essential medicines list since 1996 and is highly affordable. However, magnesium sulfate has not achieved widespread usage in developing countries. This is due to lack of public awareness of the drug, lack of adequate service-provider training, and lack of availability of magnesium sulfate in these areas.
Magnesium Sulfate Injection, USP 50%
Magnesium Sulfate Injection, USP 50% is a sterile, nonpyrogenic, concentrated solution of magnesium sulfate heptahydrate in Water for Injection. It is administered by the intravenous (IV) or intramuscular (IM) routes as an electrolyte replenisher or anticonvulsant. Must be diluted before IV use.
Each mL contains: Magnesium sulfate heptahydrate 500 mg; Water for Injection q.s. Sulfuric acid and/or sodium hydroxide may have been added for pH adjustment. The pH of a 5% solution is between 5.5 and 7.0. (Osmolarity: 4060 mOsmol/L (calc.); 2.03 mM/mL magnesium sulfate anhydrous; 4.06 mEq/mL magnesium sulfate anhydrous).
The solution contains no bacteriostat, antimicrobial agent or added buffer (except for pH adjustment) and is intended only for use as a single dose injection. When smaller doses are required the unused portion should be discarded with the entire unit. Magnesium sulfate heptahydrate is chemically designated MgSO4•7H2O, with a molecular weight of 246.47 and occurs as colorless crystals or white powder freely soluble in water.
Indications and usage
Magnesium Sulfate Injection, USP is suitable for replacement therapy in magnesium deficiency, especially in acute hypomagnesemia accompanied by signs of tetany similar to those observed in hypocalcemia. In such cases, the serum magnesium level is usually below the lower limit of normal (1.5 to 2.5 mEq/L) and the serum calcium level is normal (4.3 to 5.3 mEq/L) or elevated.
In total parenteral nutrition (TPN), magnesium sulfate may be added to the nutrient admixture to correct or prevent hypomagnesemia which can arise during the course of therapy. Magnesium sulfate injection is also indicated for the prevention and control of seizures in pre-eclampsia and eclampsia, respectively.
Magnesium for Pre-Eclampsia
This is the anticonvulsant of choice for the treatment of Eclampsia. Magnesium appears to act primarily by relieving cerebral vasospasm. The intravenous (IV) route is preferred (intramuscular injections are painful and are complicated by local abscess formation in 0.5% of cases).
Magnesium Sulphate Regime
The 20% solution is to be utilised (where available) given that the 50% solution would need diluting prior to administration. Draw up 60ml of 20% solution, ie. 48mmol.
Loading Dose: 16mmol given by slow IV injection over 5 to 10 minutes (20ml of 20% solution)
Maintenance dose: 4mmol/hr for 24 hours (or 24 hours after the last seizure). Infuse at 5mls/hr via syringe driver
Parenteral administration of the drug is contraindicated in patients with heart block or myocardial damage.
Continuous administration of magnesium sulfate beyond 5 to 7 days to pregnant women can lead to hypocalcemia and bone abnormalities in the developing fetus. These bone abnormalities include skeletal demineralization and osteopenia.
In addition, cases of neonatal fracture have been reported. The shortest duration of treatment that can lead to fetal harm is not known. Magnesium sulfate should be used during pregnancy only if clearly needed.
If magnesium sulfate is given for treatment of preterm labor, the woman should be informed that the efficacy and safety of such use have not been established and that use of magnesium sulfate beyond 5 to 7 days may cause fetal abnormalities.
This product contains aluminum that may be toxic. Aluminum may reach toxic levels with prolonged parenteral administration if kidney function is impaired. Premature neonates are particularly at risk because their kidneys are immature, and they require large amounts of calcium and phosphate solutions, which contain aluminum.
Research indicates that patients with impaired kidney function, including premature neonates, who receive parenteral levels of aluminum at greater than 4 to 5 mcg/kg/day accumulate aluminum at levels associated with central nervous system and bone toxicity. Tissue loading may occur at even lower rates of administration.
Since magnesium is distributed into milk during parenteral magnesium sulfate administration, the drug should be used with caution in nursing women.