Magnesium Sulfate and Acute Severe Asthma?

James E. Gern, MD


February 11, 2005


What dose of intravenous (IV) magnesium sulfate should be used in the treatment of acute severe asthma?

Response from James E. Gern, MD

There have been a number of studies to evaluate the usefulness of IV magnesium sulfate (MgSO4) in the treatment of acute exacerbations of asthma, and most have used 1.2-2 g IV over 20 minutes administered soon after the subject presented for care.[1] The MgSO4 was generally administered in combination with standard asthma therapy such as nebulized beta-adrenergic agonists and either oral or IV corticosteroid. In general, no benefits have been observed in subjects with mild-to-moderate airway obstruction, but there is some evidence that MgSO4 might be efficacious in subjects with severe airway obstruction.

For example, in a large multicenter study of 248 subjects with acute severe asthma, treatment with MgSO4 2 g IV was beneficial in the subset of patients who presented with severe airway obstruction (forced expiratory volume in 1 second [FEV1] < 25% predicted), but not in subjects with less severe airway obstruction.[2] However, not all investigators have found benefits in severely affected individuals. Porter and colleagues[3] conducted a double-blinded placebo-controlled trial involving 42 subjects who presented to an emergency department with a peak expiratory flow rate < 100 L/min (or < 25% predicted). Treatment with MgSO4 2 g IV in addition to standard therapy was not helpful, and in fact, the treated subjects had significantly lower peak expiratory flow rate (PEFR) 1 hour after receiving the medication.

In summary, the use of IV magnesium in acute severe asthma remains controversial, but can be considered for patients with acute severe asthma who do not respond to standard therapy. Additional studies are needed to better define which patients are most likely to benefit from this treatment.


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