Magnesium Sulphate IV (Acute Asthma)

How it works

Magnesium relaxes bronchial smooth muscle, partly by inhibiting calcium influx, producing bronchodilation that supplements standard treatment during a severe attack.

Prescribing in practice

• Give as a controlled single intravenous dose under monitoring — over-administration causes hypotension, flushing, loss of reflexes and respiratory depression, so it should be administered slowly with observation.
• Use with particular caution in renal impairment, where magnesium accumulates and toxicity is more likely.
• It is an adjunct after, not a replacement for, oxygen, inhaled bronchodilators and systemic corticosteroids in acute asthma.

Monitoring

Monitor blood pressure, respiratory rate, tendon reflexes and clinical response during and after the infusion, with particular vigilance in renal impairment.

Counselling the patient

• You may feel warm or flushed during the infusion, which is expected.
• Tell staff at once if you feel faint, very weak or more breathless.

Evidence & guidelines

A single IV magnesium sulphate infusion is recommended in BTS/SIGN and NICE acute asthma guidance for severe attacks not responding to initial therapy.