Current issues of ACP Journal Club are published in Annals of Internal Medicine


Review: Magnesium sulfate is effective for severe acute asthma treated in the emergency department

ACP J Club. 1999 Sept-Oct;131:36. doi:10.7326/ACPJC-1999-131-2-036

Source Citation

Rowe BH, Bretzlaff JA, Bourdon C, Bota GW, Camargo CA Jr. Magnesium sulfate treatment for acute asthmatic exacerbations treated in the emergency department. Cochrane Review, latest version 23 Feb 1999. In: The Cochrane Library. Oxford: Update Software.



What is the effectiveness of intravenous magnesium sulfate in patients with acute asthma who were treated in the emergency department?

Data sources

Studies were identified from the Cochrane Airways Review Group Register, MEDLINE, EMBASE/Excerpta Medica, CINAHL, and the Cochrane Library; hand searches of 20 high-quality respiratory journals; bibliographies of relevant papers; and contact with authors and content experts.

Study selection

Studies were selected if they were randomized controlled trials or quasi-randomized trials, included adults or children presenting to an emergency department with acute asthma, and compared intravenous magnesium sulfate with placebo.

Data extraction

Data were extracted on study and patient characteristics, hospital admissions, pulmonary function, vital signs, and adverse events.

Main results

27 studies were reviewed for inclusion, and 7 trials (665 patients; 5 of adult and 2 of pediatric patients; 6 from the United States and 1 from India) met the inclusion criteria. Analyses of all patients and of patients with severe asthma showed a reduction in hospital admission rates (Table), whereas no difference was shown for patients with mild-to-moderate asthma. Studies that included all patients showed no differences in measures of pulmonary function (peak expiratory flow rate or FEV1) or vital signs (heart rate, respiratory rate, or blood pressure). In studies of patients with severe asthma, peak expiratory flow rate improved by 52 L/min (95% CI 27 to 78 L/min; 3 studies) and FEV1 by 8% of the predicted value (CI 5% to 12%; 3 studies). Data were insufficient to assess adverse events.


Intravenous magnesium sulfate reduces the rate of hospital admissions and improves pulmonary function in patients with severe acute asthma treated in the emergency department.

Sources of funding: Canadian Association of Emergency Physicians and National Institutes of Health.

For correspondence: Dr. B.H. Rowe, Division of Emergency Medicine, University of Alberta, 1G1 Walter Mackenzie Centre, 8440-112 Street, Edmonton, Alberta T6G 2B7, Canada. FAX 403-492-9857.

Table. Magnesium sulfate vs placebo for hospital admissions among patients with acute asthma at end of study*

Patients Weighted event rates RRR (95% CI) NNT (CI)
Magnesium sulfate Placebo
All 23% 45% 30% (2 to 49) 5 (3 to 63)
Severe asthma 51% 91% 44% (29 to 56) 3 (2 to 4)

*Abbreviations defined in Glossary; RRR, NNT, and CI calculated from data in article.


The systematic review by Rowe and colleagues is an important addition to the management of acute asthma. Optimal therapy currently consists of bronchodilation with short-acting β-2 agonists, adjunct therapy with ipratropium bromide (in more severe disease), oxygen, and corticosteroids (1). The results of this review indicate that magnesium sulfate reduces hospital admission in patients with an FEV1 < 30% at presentation or those who do not respond to initial treatment or improve beyond 60% after 1 hour.

It is tempting to extrapolate from these data that all patients with moderately severe acute asthma should receive magnesium sulfate. An important consideration, however, is the discretionary use of adjunct therapies, such as aminophylline (2 studies) and ipratropium bromide (1 study), included in the meta-analysis. Both these interventions have been shown to reduce hospital admission rates without improving lung function (2-4). Until patients with less severe obstruction treated with these therapies show greater benefit with the incremental addition of magnesium sulfate than with placebo, magnesium sulfate should be reserved for patients who fulfill the above criteria.

J. Mark FitzGerald, MD
Vancouver General HospitalVancouver, British Columbia, Canada


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2. Wrenn K, Slovis CM, Murphy F, Greenberg RS. Aminophylline therapy for acute bronchospastic disease in the emergency room. Ann Intern Med. 1991;115:241-7.

3. Lanes SF, Garrett JE, Wentworth CE 3rd, FitzGerald JM, Karpel JP. The effect of adding ipratropium bromide to salbutamol in the treatment of acute asthma: a pooled analysis of three trials. Chest. 1998;114:365-72.

4. Qureshi F, Pestian J, Davis P, Zaritsky A. Effect of nebulized ipratropium on the hospitalization rates of children with asthma. N Engl J Med. 1998;339:1030-5.