Drug Study: magnesium sulfate

Generic and brand name: magnesium sulfate 250 mg/mL (25%) solution for injection
Category: anticonvulsant

Description: magnesium sulfate 250 mg/mL (25%) injection is a sterile, pyrogen-free solution of magnesium sulfate in water for injection.

Each mL contains: magnesium sulfate (anhydrous) = 250mg; water for injection, q.s. ad. = 1mL; no preservative added

Mechanism of action:
Magnesium sulfate inhibits convulsion by acting at the myoneural junction to prevent release of acetylcholine and to decrease the motor and plate potential. It inhibits the contraction of the uterus by directly acting on the myometrial cells and enhancing uterine blood flow.

Indications: magnesium sulfate is indicated for the treatment of acute hypomagnesemia accompanied by signs of tetany, to control hypertension, encephalopathy and convulsions and for the prevention and control of convulsions in patients with pre-eclampsia or eclampsia. It is also used to prevent hypomagnesemia in patients receiving total parenteral nutrition (TPN).

Dosage and administration:

Magnesium deficiency, adult: 2 mL injected intramuscularly every 6 hours for 4 doses
Nephritic seizures in children: 0.05 – 0.1 mL per kg body weight injected intramuscularly as needed
Pre-eclampsia: 8 to 10 mL added into a 250 mL of 5% dextrose or 0.9% sodium chloride injection administered by intravenous infusion. Simultaneously, intramuscular dose of up to 20 mL of the undiluted solution may be given (10 mL in each buttock). Thereafter, 8 to 10 mL is injected intramuscularly into alternate buttocks depending on the presence of patellar reflex and adequate respiratory function. Therapy should be continued until paroxysms cease. Appropriate reduction in dosage should be made for patients with renal impairment.

Note: an isotonic solution of Magnesium Sulfate may be prepared by aseptically adding 7.3 mL of Magnesium Sulfate 250mg/mL injection to a 50mL of Sterile water for injection of other suitable parenteral solvent.

About one third or orally administered Magnesium Sulfate is absorbed which is enhanced by the presence of the Vitamin D compound Calcitrol. It readily crosses the placenta but rarely causes toxicity to the neonate. Toxicity in the mother is indicated by the loss of patellar reflex which occurs when the blood level of magnesium is between 7 to 10 mEq/L.

Adverse effects:

Adverse effects due to high level of magnesium ion include flushing, sweating, hypotension, muscular weakness, sedation and confusion. As the blood level begins to exceed 4 mEq/L, deep tendon reflexes are decreased which may be absent at 10mEq/L. At 12 to 15 mEq/L, respiratory paralysis is a potential hazard.

Treatment of Adverse effects:

An injectable solution of calcium salt (i.e. as gluconate) should always be available for use as antidote. Calcium salt injection should be administered intravenously at a dose of up to 10mEq to counteract respiratory depression or heart block. If renal function is normal, adequate fluid should be given to assist removal of magnesium from the body. Dialysis may be necessary in patients with renal impairment or severe hypermagnesemia.


Use with extreme caution to patients with impaired renal function and those receiving digitalis glycosides. Magnesium Sulfate injection may enhance the effects of neuromuscular blocking agents.

Magnesium Sulfate injection is contraindicated to patients with heart block or myocardial damage.

foods drugs, devices and cosmetics act prohibits dispensing without prescription

Storage condition: store at temperatures not exceeding 30 degrees Celsius.

Availability: magnesium sulfate 250mg/mL (25%) injection is available in clear vials with 10 mL content.

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