Magnesium Sulphate

Magnesium Sulphate

[1 vial $2.66]

ADMINISTRATION ROUTES:

  • IV

ALTERNATIVE NAMES:

  • Magnesium Sulphate injection BP 49.3%

ICU INDICATIONS:

  1. hypomagnaesia
  2. atrial arrhythmias, torsades de pointes and ventricular ectopy
  3. eclampsia
  4. asthma

PRESENTATION AND ADMINISTRATION:

  • IV:
    Injection 49.3% in 5ml solution contains 10mmol of magnesium sulphate
    Store at room temperature
    May be administered by direct IV injection provided that the concentration injected does not exceed 20% and the rate of infusion does not exceed 150mg/min (0.75ml/min of 20% solution).
    A 20% solution can achieved by diluting 5ml of 49.3% solution with at least 12.5ml of compatible IV fluid.
    In an emergency, to treat torsade de pointes, 10mmol can be administered by direct IV injection over 1-2 minutes (preferably via a central line).
    The usual means of administration in ICU is by intermittent infusion. When magnesium sulphate is administered by intermittent or continuous infusion, the required dose should be added to 50-500ml of compatible IV fluid and mixed thoroughly before being infused over 20-60 minutes at a rate no greater than 150mg/min.
    Compatible with the following IV fluids:
    Normal saline glucose and sodium chloride, 5% & 10% dextrose, Hartmanns

DOSAGE:

  • IV:
    Hypomagnesaemia, atrial arrhythmias and ventricular ectopy

    10-20 mmol IV over 20-60 minutes
    Eclampsia

    Commence with a loading dose of 20mmol of Magnesium Sulphate in 100mls of normal saline administered over 20 minutes. For maintenance infusion add 40mmol to 500ml normal saline. Commence infusion at 50ml/hr (approximately 1gm/hr) if the patient weighes <55kg. Commence infusion at 75ml/hr (approximately 1.5gm/hr) if the mother weighs >55kg
    The target serum magnesium concentration in eclampsia is 2.0-3.0 mmol/L.
    Torsades de pointes
    10mmol over 1-2 minutes followed by 20mmol over 6 hours.
    Severe asthma
    Boluses of 5-10mmol can be given over 20 minutes or a continuous infusion can administered by diluting 100mmol in 100ml of compatible IV fluid and running at 5ml/hr (5mmol/hr)

DOSAGE IN RENAL FAILURE AND RENAL REPLACEMENT THERAPY:

  • Specific recommendations for dosage in renal failure are not available; however, patients with renal failure are at increased risk of magnesium toxicity (particularly when infusions are used) and dose reduction may be required.

DOSAGE IN PAEDIATRICS:

  • IV:
    Hypomagnesaemia
    0.2ml/kg
    Asthma
    IV magnesium sulphate bolus. Use magnesium sulphate 49.3% (493mg/ml). Give 0.1 ml/kg (approx 50mg/kg) over 20 minutes (dilute to 20mls with normal saline and infuse via syringe driver). Maximum dose 5 mls (2.5 g).

CLINICAL PHARMACOLOGY:

  • 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.

CONTRAINDICATIONS:

  1. heart block (unless pacing wires are present)

WARNINGS

  • Hypermagnesaemia
    The principal hazard in parenteral magnesium therapy is the production of abnormally high levels of magnesium in the plasma. The most immediate danger to life is respiratory depression. Calcium chloride or calcium gluconate provide an effective antidote to life threatening hypermagnesaemia.
  • Toxicity in the newbon
    When Magnesium Sulphate, is administered intravenously by a continuous infusion for longer than 24 hours before delivery, the possibility of the baby’s showing signs of neuromuscular or respiratory depression of the newborn should be considered, since foetal toxicity can occur. A baby with hypermagnesemia my require resuscitation and assisted ventilation.

PRECAUTIONS

  • General:
    Since Magnesium is excreted almost entirely by the kidneys, it should be given very cautiously in the presence of serious impairment of renal function.
  • Laboratory Tests: Patients with eclampsia treated with magnesium by infusion should have serum magnesium levels measured 6 hourly until stability is achieved. Target serum magnesium concentration in eclampsia is 2.0-3.0 mmol/L.
  • Drug/Laboratory Test Interactions: None known.

IMPORTANT DRUG INTERACTIONS FOR THE ICU

  • When barbiturates, narcotics, hypnotics (or systemic anesthetics), or other central nervous system depressants are to be given in conjunction with magnesium, their dosage should be adjusted with caution because of the additive central nervous system depressant effects of magnesium.

ADVERSE REACTIONS

  • Principal adverse reactions are related to the high plasma levels of magnesium and include flushing, sweating, hypotension, circulatory collapse, and cardiac and central nervous system depression. Respiratory depression is the most life-threatening effect.

Critical Care Drug Manual

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