MAGNESIUM

What it is

Magnesium Sulfate Heptahydrate 50% Concentrated Injection contains magnesium sulfate heptahydrate 500 mg per mL. This is equivalent to 2 mmol (4 mEq) of magnesium ions and 2 mmol (4 mEq) of sulfate ions in each mL. The injection is a clear, colourless, slightly viscous, sterile solution.

Approved indications

Magnesium Sulfate Heptahydrate 50% Concentrated Injection is indicated for: — Treatment of acute hypomagnesaemia. — Prevention of hypomagnesaemia in patients receiving total parenteral nutrition. — Prevention and treatment of life-threatening seizures in the treatment of toxemias of pregnancy (pre-eclampsia and eclampsia). — Emergency treatment of some arrhythmias such as Torsade de Pointes and those associated with hypokalemia.

Dosing overview

Careful monitoring of plasma magnesium and other electrolyte concentration is essential whenever using this preparation. Magnesium Sulfate Heptahydrate 50% Concentrated Injection is administered intravenously or intramuscularly. Intravenous doses should be diluted to a concentration of 20% magnesium or less, with each 5 mL vial diluted by adding at least 7.5 mL of a compatible solution, and each 10 mL vial diluted with at least 15 mL of a compatible solution. The total adult daily dose should not exceed 30–40 g of magnesium sulfate per day.

Key safety warnings

Respiration rate should be determined and should be at least 16 per minute prior to each dose of magnesium sulfate, as respiratory depression is the most critical side effect of the medication. The patellar reflex should be tested prior to administering repeat doses, and suppression of the reflex is an indication of magnesium intoxication. Urine output should be monitored and should be at least 100 mL during the four hours preceding dosing, to ensure adequate excretion of magnesium. Magnesium Sulfate Heptahydrate 50% Concentrated Injection may precipitate an acute myasthenic crisis. An intravenous preparation of a calcium salt should always be available in case of toxicity. Concurrent use of magnesium salts and CNS depressant drugs may result in an enhanced CNS depressant effect. Concurrent use with neuromuscular blocking agents such as tubocurarine, suxamethonium and vercuronium may result in an excessive neuromuscular blockade.

Contraindications

Magnesium Sulfate Heptahydrate 50% Concentrated Injection is contraindicated in patients with heart block, since magnesium may exacerbate this condition, and in patients with renal failure (creatinine clearance less than 20 mL/min) or hepatic disorders, since there is an increased risk of hypermagnesaemia in these patients. The injection should not be administered to pregnant women in the two hours prior to delivery, unless it is the only therapy available to prevent eclamptic seizures, as there is a risk that the neonate will be born with hypermagnesaemia and depressed breathing.

Regulatory history

Magnesium Sulfate Heptahydrate 50% Concentrated Injection was first approved on 14 October 1991.