What is the recommended dose and preparation of magnesium sulfate for an adult with an acute asthma exacerbation?

From the Guidelines

For adults with acute asthma exacerbation, intravenous magnesium sulfate can be administered at a dose of 2 grams infused over 20 minutes, as recommended by the most recent and highest quality study 1. The medication should be diluted in 50-100 mL of normal saline solution before administration. This therapy is typically reserved for patients with severe exacerbations who have not adequately responded to initial bronchodilator treatments. Some key points to consider when administering magnesium sulfate include:

• Magnesium sulfate works by causing bronchial smooth muscle relaxation, which helps reduce airway constriction and improve airflow.
• It also has anti-inflammatory properties that may help decrease airway inflammation during an asthma attack.
• When administering magnesium sulfate, patients should be monitored for potential side effects including hypotension, flushing, and respiratory depression.
• This treatment should be used as an adjunct to standard asthma therapies including inhaled beta-agonists, anticholinergics, and systemic corticosteroids, not as a replacement for these first-line treatments.
• The onset of action is relatively quick, with potential improvement in lung function occurring within 30-60 minutes after administration, as supported by the evidence 1. Other treatments for acute asthma exacerbation, such as inhaled short-acting beta2-agonists, anticholinergics, and systemic corticosteroids, are discussed in the guidelines 1, but the focus for magnesium sulfate dosing and preparation remains on the 2 grams infused over 20 minutes for adults.

From the Research

Magnesium Sulfate Dose and Preparation for Adults with Asthma

• The recommended dose of magnesium sulfate for adults with acute asthma exacerbation is 1.2 g or 2 g administered intravenously over 15 to 30 minutes 2.
• Nebulised magnesium sulfate may be used, but the evidence for its effectiveness is limited and it is not recommended for routine use 3.
• The preparation of magnesium sulfate for intravenous administration is typically a solution of 2 g in 20 mL of water, administered over 20 minutes 4.

Administration and Monitoring

• Magnesium sulfate should be administered in a monitored setting, with careful observation of the patient's vital signs and respiratory status 2.
• The patient's peak expiratory flow rate (PEFR) and forced expiratory volume in one second (FEV1) should be monitored before and after administration of magnesium sulfate to assess its effectiveness 5.

Safety and Adverse Events

• Magnesium sulfate is generally well-tolerated, but may cause adverse events such as flushing, fatigue, nausea, and headache 2.
• Hypotension (low blood pressure) is a potential adverse event, and patients should be monitored for signs of hypotension during administration of magnesium sulfate 2.
• The risk of adverse events is higher with intravenous administration than with nebulised administration 4, 3.

Clinical Guidelines and Recommendations

• The use of magnesium sulfate in acute asthma is recommended in selected cases, particularly in severe exacerbations 6.
• Current guidelines recommend the use of intravenous magnesium sulfate in adults with acute asthma who have not responded sufficiently to oxygen, nebulised short-acting beta2-agonists, and IV corticosteroids 2, 6.