Magnesium Sulphate IV (Additional Indications)

How it works

Given intravenously, magnesium acts as a calcium antagonist and membrane stabiliser, relaxing bronchial and vascular smooth muscle and suppressing triggered cardiac activity that drives torsades.

Prescribing in practice

• Magnesium toxicity (loss of reflexes, respiratory depression, hypotension) is the principal danger, so monitor clinically and keep intravenous calcium available as the antidote.
• Lower the dose and monitor more intensively in renal impairment, where magnesium accumulates rapidly.
• Control the infusion rate, as rapid intravenous administration can precipitate flushing, hypotension and bradycardia.

Monitoring

Monitor reflexes, respiratory rate, blood pressure, cardiac rhythm and urine output during infusion, with serum magnesium levels in renal impairment or repeated dosing.

Counselling the patient

• Flushing or a feeling of warmth during the drip is common and usually settles quickly.
• Alert staff immediately if you feel weak, very drowsy or short of breath.

Evidence & guidelines

Intravenous magnesium as adjunct in severe asthma and for torsades de pointes is supported by national asthma guidance and resuscitation council recommendations.