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    Last updated: June 2023


    Prescription under medical supervision


    Therapeutic action

    • Calcium antagonist, anticonvulsant


    • Severe pre-eclampsia: prevention of eclamptic seizures
    • Eclampsia: treatment of eclamptic seizures and prevention of recurrence

    Forms and strengths, route of administration

    • 5 g ampoule (0,5 g/ml, 10 ml) for IM injection or IV infusion 

    Dosage and duration

    IV/IM protocol

    4 g by IV infusion in 100 ml of 0.9% sodium chloride over 15 to 20 minutes then, 10 g by IM route (5 g in each buttock) then, 5 g by IM route every 4 hours (changing buttock for each injection)


    IV protocol

    4 g by IV infusion in 100 ml of 0.9% sodium chloride over 15 to 20 minutes then 1 g per hour by continuous IV infusion


    Regardless of the protocol chosen:

    • Continue the treatment for 24 hours after the delivery or the last seizure.
    • If seizures persist or recur, administer a further 2 g (patients less than 70 kg) to 4 g by IV infusion, without exceeding 8 g total dose during the first hour.

    Contra-indications, adverse effects, precautions

    • Reduce the dose in patients with renal impairment; do not administer to patients with severe renal impairment.
    • May cause:
      • pain at the injection site, warm flushes; decreased fetal heart rate;
      • in case of overdosage (hypermagnesaemia): 
        • For the mother: diminished then absent patellar reflex (early sign), hypotension, drowsiness, confusion, difficulty in speaking, bradycardia, respiratory depression (respiratory rate < 12/minute).
        • For the neonate (if the mother is treated for pre-eclampsia or eclampsia): hypotonia, neurobehavioural impairment, apnoea, respiratory depression.
    • Do not combine with nifedipine.
    • Check urine output every hour. In the event of decreased urine output (< 30 ml/hour or 100 ml/4 hour), stop magnesium sulfate and perform delivery as soon as possible. If delivery cannot be performed immediately in a woman with eclampsia, stop magnesium sulfate for one hour then resume magnesium sulfate perfusion until delivery.
    • Check patellar reflex, blood pressure, heart and respiratory rate every 15 minutes during the first hour of treatment. If no signs of overdosage are observed, continue this surveillance every hour. If signs of overdosage are observed: stop magnesium sulfate and give 1 g calcium gluconate by slow IV route as an antidote (in this event, seizures may recur).
    • Breast-feeding: no contra-indication


    • Magnesium sulfate is also used as an adjunctive treatment in severe asthma attack in children and adults: 40 mg/kg (max. 2 g) by IV infusion in 5 ml/kg of 0.9% of sodium chloride in children less than 20 kg and in 100 ml of 0.9% sodium chloride in children 20 kg and over and in adults, to be administered over 20 minutes, using an infusion or a syringe pump.
    • Also comes in ampoules containing 1 g (0.5 mg/ml, 2 ml) and many other dosages. Check the strength of the ampoule carefully before use.
    • 1 g magnesium sulfate contains approximately 4 mmol (8 mEq) of magnesium.
    • Do not mix with other drugs in the same syringe or infusion fluid.


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