Magnesium Sulphate

Uses

Magnesium sulfate injection is used for the following conditions:

Convulsions (treatment) - Intravenous Magnesium sulfate injection is used for immediate control of life-threatening convulsions in the treatment of severe toxemias (pre-eclampsia and eclampsia) of pregnancy and in the treatment of acute nephritis in children.

Hypomagnesemia (prophylaxis and treatment) - Magnesium sulfate injection is used for replacement therapy in magnesium deficiency, especially in acute hypomagnesemia accompanied by signs of tetany similar to those of hypocalcemia.

Magnesium sulfate injection is also used to prevent or treat magnesium deficiency in patients receiving total parenteral nutrition.

Tetany, uterine (treatment) - Magnesium sulfate injection is used for uterine tetany as a myometrial relaxant.

Magnesium Sulphate is also used to associated treatment for these conditions: Constipation, Convulsions, Hypomagnesemia, Torsades de Pointes, Barium poisoning, Severe Exacerbation of asthma, Bowel preparation therapy, Soaking aid for minor sprains and bruises

How Magnesium Sulphate works

Magnesium is the second most plentiful cation of the intracellular fluids. It is essential for the activity of many enzyme systems and plays an important role with regard to neurochemical transmission and muscular excitability. Magnesium sulfate reduces striated muscle contractions and blocks peripheral neuromuscular transmission by reducing acetylcholine release at the myoneural junction. Additionally, Magnesium inhibits Ca²⁺ influx through dihydropyridine-sensitive, voltage-dependent channels. This accounts for much of its relaxant action on vascular smooth muscle.

Dosage

Magnesium Sulphate dosage

Intramuscular:Adults and older children: For severe hypomagnesemia, 1 to 5 g (2 to 10 mLof 50% solution) daily in divided doses; administration is repeated daily until serum levels have returned to normal. If deficiency is not severe, 1 g (2 mL of 50% solution) can be given once or twice daily. Serum magnesium levels should serve as a guide to continued dosage.

Intravenous:1 to 4 g magnesium sulfate (magnesium sulfate (magnesium sulfate injection) injection) may be given intravenously in 10% to 20% solution, but only with great caution; the rate should not exceed 1.5 mL of 10% solution or equivalent per minute until relaxation is obtained.

Intravenous Infusion:4 g in 250 mL of 5% Dextrose Injection at a rate not exceeding 3 mL per minute.

Usual Dose Range:1 to 40 g daily.

Electrolyte Replenisher:Intramuscular 1 to 2 g in 50% solution four times a day until serum magnesium is within normal limits.

Usual Pediatric Dose:Intramuscular 20 to 40 mg per kg of body weight in a 20% solution repeated as necessary.

For Eclampsia:Initially 1 to 2 g in 25% or 50% solution is given intramuscularly. Subsequently, 1 g is given every 30 minutes until relief is obtained. The blood pressure should be monitored after each injection.

Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.

Side Effects

Flushing, sweating, sharply lowered blood pressure, hypothermia, stupor and ultimately, respiratory depression.

Toxicity

LD₅₀ = 1200 mg/kg (rat, subcutaneous). May be harmful if swallowed. May act as an irritant. Adverse reactions include hypotension, ECG changes, diarrhea, urinary retention, CNS depression and respiratory depression.

Precaution

Renal impairment, myasthaenia gravis, digitalised patients; pregnancy. Monitor serum-magnesium concentrations.

Food Interaction

Half Life

43.2 hours (for newborns)

Elimination Route

Magnesium is excreted solely by the kidney at a rate proportional to the serum concentration and glomerular filtration.

Pregnancy & Breastfeeding use

Pregnancy category B. Either animal-reproduction studies have not demonstrated a foetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the 1st trimester (and there is no evidence of a risk in later trimesters).

Contraindication

Heart block, severe renal impairment, myocardial damage.

Acute Overdose

Symptoms of hypermagnesaemia are: respiratory depression and loss of deep tendon reflexes due to neuromuscular blockade; nausea, vomiting, flushing, thirst, hypotension, drowsiness, confusion, slurred speech, double vision, bradycardia and muscle weakness.

Treatment in adults should include IV administration of 5-10 mEq of 10% calcium gluconate. Artificial respiration may be required.

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