Magnesium Sulfate

Magnesium is an essential constituent of many enzyme systems, particularly those involved in energy generation; the largest stores are in the skeleton.

• Each 5 ml ampoule of injection contains 50% solution of Magnesium sulphate heptahydrate BP (Mg²+ approx. 2 mmol/ml), total 2.47gm.
• Each 100 ml bottle of infusion contains 4% solution of Magnesium sulphate heptahydrate BP (Mg²⁺ approx. 0.16 mmol/ml), total 4 gm.

Magnesium is given initially by intravenous infusion or by intramuscular injection of Magnesium sulphate. The intramuscular injection is painful. Plasma magnesium concentration should be measured to determine the rate and duration of infusion and the dose should be reduced in renal impairment. Intravenous administration concentration of magnesium sulphate should not exceed 20%. Dilute 1 part of magnesium sulphate injection 50% with at least 1.5 parts of water for injection.

Eclampsia and pre-eclampsia: Magnesium sulphate is the drug of choice for the prevention of recurrent seizures in eclampsia, initially by intravenous injection over 5-15 minutes, 4g followed by intravenous infusion, 1g/hour for at least 24 hours after last seizure; if seizure occurs, additional dose of intravenous injection of 2g. (Regimens may vary between hospitals; calcium gluconate injection is used for the management of magnesium toxicity).

Arrhythmias: Magnesium sulphate has also been recommended for the emergency treatment of serious arrhythmias, especially in the presence of hypokalaemia (when hypomagnesaemia may also be present) and when salvos of rapid ventricular tachycardia show the characteristic twisting wave front known as torsades de pointes. The usual dose of magnesium sulphate by intravenous injection is 8 mmol Mg2+ over 10-15 minutes (repeated if necessary).

Myocardial Infarction: Evidence suggesting a sustained reduction in mortality in patients with suspected myocardial infarction given an initial intravenous injection of magnesium sulphate 8 mmol Mg2+ over 20 minutes followed by an intravenous infusion of 65-72 mmol Mg2+ over the following 24 hours, has not been borne out by a larger study. Some, however, continue to hold the view that magnesium is beneficial if given immediately (and for as long as beneficial likelihood of reperfusion taking place).

Severe Asthma: Severe asthma may be helped by intravenous infusion of magnesium sulphate 1.2-2g over 20 minutes.

Hypomagnesaemia: Since magnesium is secreted in large amounts in the gastro-intestinal fluid, excessive losses in diarrhoea, stoma or fistula are the most common causes of hypomagnesaemia, deficiency may also occur in alcoholism or as a result of treatment with certain drugs. Hypomagnesaemia often causes secondary hypocalcaemia and also hypokalaemia and hyponatraemia.

Magnesium is the second most plentiful cation of 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. Deficits are accompanied by a variety of structural and functional disturbances.

Adult dose-

• Intramuscular: For severe hypomagnesemia, 1 to 5 g (2 to 10 mL of 50% solution) daily in divided doses; administration is repeated daily until serum levels have returned to normal. If the 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 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.
• 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.

Use in Children & Adolescents: Magnesium Sulfate seems to be beneficial in the treatment of moderate to severe asthma in children as adjuvant therapy.

With medicine: Magnesium Sulfate may cause a reduction in blood pressure when taken together with Calcium channel blockers such as nifedipine. There may be an increase in the effects of neuromuscular blocking agents when given together with Magnesium Sulfate. When Magnesium Sulfate is given together with the following medicines there may be a risk of respiratory depression on high-dose barbiturates, opioids and aminoglycosides antibiotics.

With food & others: There is no interaction of Magnesium Sulfate with food & others.

Magnesium Sulfate contra-indicated in the case of a defect of the heart's electrical message pathways resulting in decreased function of the heart (heart block), severe damage to the muscular wall of the heart (myocardium) and significantly decreased kidney function.

Common: Excessive administration of magnesium leads to the development of hypermagnesaemia. Symptoms of hypermagnesaemia may include nausea, vomiting, flushing of skin, thirst, hypotension due to peripheral vasodilatation, drowsiness, confusion, muscle weakness etc.

Rare: Diarrhea or skin irritation after soaking may occur.

Magnesium Sulfate crosses the placenta. So, as with any other drugs, caution is required when the drug is administered to pregnant women. It is not known whether the drug is excreted in human milk. As it happens with many other drugs, cautions should be taken when it is administered to a nursing mother.

Magnesium salts should be administered with caution to patients with impaired renal function or those receiving digitalis glycosides. Parenteral administration of magnesium salts may enhance the effect of neuromuscular blocking agents or of central nervous system depressants. Monitor blood pressure, respiratory rate, urinary output and for signs of over dosage like loss of patellar reflex, weakness, nausea, sensation of warmth, flushing of skin, drowsiness, double, vision and slurred speech.

Symptoms of hypermagnesemia 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.

Specific mineral preparations

Store in a cool & dry place, keep away from light & children.