3Mg Study

The 3Mg Study: A randomised trial of intravenous (IV) or nebulised magnesium sulphate versus placebo for acute severe asthma


The 3Mg Study aimed to determine whether IV or nebulised magnesium sulphate should be standard first-line treatment for patients with acute severe asthma. The trial tested whether IV or nebulised magnesium sulphate could reduce the proportion of patients who require admission at initial presentation or during the following week, and/or improve the patient´s assessment of their breathlessness over two hours after initiation of treatment.

The trial recruited 1109 people with acute severe asthma at 34 hospitals between July 30, 2008, and June 30, 2012. Participants were randomised to IV or nebulised magnesium sulphate or placebo. The co-primary outcomes were (1) admission to hospital at presentation or any time over the following week and (2) visual analogue scale (VAS) breathlessness over two hours following treatment.

We were unable to demonstrate a clinically worthwhile benefit from magnesium sulphate in acute severe asthma. There was some weak evidence of an effect of IV magnesium sulphate on hospital admission, but no evidence of an effect on VAS breathlessness or PEFR compared with placebo. We found no evidence that nebulised magnesium sulphate was more effective than placebo.

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