Magnesium sulfate

Macromineral·Vitamins & Minerals

Hypomagnesemia, Eclampsia (seizure prevention), Torsades de Pointes, severe acute asthma

MINERAL IVMagnesium Sulfate 50%Ampoules (usually 10 mmol or…S4TGA

Max Dose

20 mmol/hr (IV)

Half-life

Minutes (Distribution)

Reflexes

LOSS = TOXICITY

Asthma/Eclampsia

RESCUE DRUG

Rapid Summary

Overview

The ultimate intravenous smooth-muscle relaxant and membrane stabilizer. Used in critical emergencies for severe asthma, Eclampsia (seizures in pregnancy), and Torsades de Pointes.

Maximum Dose

Titrated closely. Standard emergency IV bolus is 10-20 mmol (2.5-5 g) over 20 mins.

Clinical Focus

Magnesium toxicity paralyzes the diaphragm. The first sign of impending respiratory arrest is the loss of deep tendon (patellar) reflexes.

Bottom Line

Magnesium sulfate is essential for eclampsia prophylaxis/treatment and severe hypomagnesaemia, but IV infusion requires reflexes and respiratory monitoring to prevent fatal overdose.

Formulation & Access

Brand Names

Magnesium Sulfate 50%

Parenteral

Ampoules (usually 10 mmol or 2.5 g per 5 mL). Concentrated solution, MUST be diluted for infusions.

Prescribing & PBS

Hospital OT/ICU/ED/Delivery Suite supply. S4.

Indications & Use

Primary

TGA

Hypomagnesemia, Eclampsia (seizure prevention), Torsades de Pointes, severe acute asthma.

Clinical Place

A 'magic bullet' in ED/ICU that instantly stabilises cardiac membranes and relaxes spasmodic muscle.

Quick reference

Class & Role

Macromineral — The ultimate intravenous smooth-muscle relaxant and membrane stabilizer.

Route / Formulation

Ampoules (usually 10 mmol or 2.5 g per 5 mL). Concentrated solution, MUST be diluted for infusions. (Magnesium Sulfate 50%)

Usual Dose & Max

IV 10 mmol (2.5 g) STAT push over 1-2 mins. Titrated closely. Standard emergency IV bolus is 10-20 mmol (2.5-5 g) over 20 mins.

Key Indication Doses

Torsades de Pointes (VT): IV 10 mmol (2.5 g) STAT push over 1-2 mins. Severe Asthma Exacerbation: IV 10 mmol (2.5 g) infused over 20 minutes (Relaxes bronchial smooth muscle). Eclampsia / Pre-eclampsia: IV 16 mmol (4 g) loading dose over 20 mins, followed by continuous infusion of 4 mmol/hour (1 g/hr).

Best Uses

Magnesium sulfate is essential for eclampsia prophylaxis/treatment and severe hypomagnesaemia, but IV infusion requires reflexes and respiratory monitoring to prevent fatal overdose.

Avoid / Cautions

Myasthenia Gravis (will instantly paralyze them), heart block, severe renal failure (eGFR < 15, will accumulate and cause coma). Pregnancy Category A. The absolute gold-standard therapy to prevent maternal death from eclamptic seizures.

Key Risks

Neurological: Hypermagnesemia causes sequential paralysis: Loss of deep tendon reflexes -> Somnolence -> Flaccid paralysis -> Apnoea -> Asystole/Cardiac Arrest. Cardiovascular: Severe hypotension, vasodilation, flushing (if pushed too fast IV). Gastrointestinal: Nausea.

Key Interactions

Calcium Channel Blockers (Nifedipine, Amlodipine). Combining IV Magnesium with high-dose CCBs causes profound, refractory hypotension and neuromuscular blockade. Non-depolarizing muscle relaxants (Rocuronium). Mag sulfate massively prolongs surgical paralysis.

Monitoring

Every 1-2 hours on infusion, you MUST test the patient's patellar (knee-jerk) reflex. If the reflex is absent, STOP the infusion immediately. Monitor SpO2, RR, and BP. Check U&E (Magnesium and Calcium levels) every 4-6 hours during prolonged infusions.

Clinical Pearl

If you overdose IV Magnesium and the patient stops breathing, the direct physiological antidote is IV Calcium Gluconate (10 mL of 10% solution). It instantly kicks the magnesium off the receptors and restores muscle function.

Access

Magnesium Sulfate 50%

Brand: Magnesium Sulfate 50%

Magnesium sulfate

Macromineral·Vitamins & Minerals

Hypomagnesemia, Eclampsia (seizure prevention), Torsades de Pointes, severe acute asthma

MINERAL IVMagnesium Sulfate 50%Ampoules (usually 10 mmol or…S4TGA

Max Dose

20 mmol/hr (IV)

Half-life

Minutes (Distribution)

Reflexes

LOSS = TOXICITY

Asthma/Eclampsia

RESCUE DRUG

Rapid Summary

Overview

The ultimate intravenous smooth-muscle relaxant and membrane stabilizer. Used in critical emergencies for severe asthma, Eclampsia (seizures in pregnancy), and Torsades de Pointes.

Maximum Dose

Titrated closely. Standard emergency IV bolus is 10-20 mmol (2.5-5 g) over 20 mins.

Clinical Focus

Magnesium toxicity paralyzes the diaphragm. The first sign of impending respiratory arrest is the loss of deep tendon (patellar) reflexes.

Bottom Line

Magnesium sulfate is essential for eclampsia prophylaxis/treatment and severe hypomagnesaemia, but IV infusion requires reflexes and respiratory monitoring to prevent fatal overdose.

Formulation & Access

Brand Names

Magnesium Sulfate 50%

Parenteral

Ampoules (usually 10 mmol or 2.5 g per 5 mL). Concentrated solution, MUST be diluted for infusions.

Prescribing & PBS

Hospital OT/ICU/ED/Delivery Suite supply. S4.

Indications & Use

Primary

TGA

Hypomagnesemia, Eclampsia (seizure prevention), Torsades de Pointes, severe acute asthma.

Clinical Place

A 'magic bullet' in ED/ICU that instantly stabilises cardiac membranes and relaxes spasmodic muscle.

Quick reference

Class & Role

Macromineral — The ultimate intravenous smooth-muscle relaxant and membrane stabilizer.

Route / Formulation

Ampoules (usually 10 mmol or 2.5 g per 5 mL). Concentrated solution, MUST be diluted for infusions. (Magnesium Sulfate 50%)

Usual Dose & Max

IV 10 mmol (2.5 g) STAT push over 1-2 mins. Titrated closely. Standard emergency IV bolus is 10-20 mmol (2.5-5 g) over 20 mins.

Key Indication Doses

Best Uses

Magnesium sulfate is essential for eclampsia prophylaxis/treatment and severe hypomagnesaemia, but IV infusion requires reflexes and respiratory monitoring to prevent fatal overdose.

Avoid / Cautions

Key Risks

Key Interactions

Monitoring

Clinical Pearl

Access

Magnesium Sulfate 50%

Brand: Magnesium Sulfate 50%