How useful is intravenous magnesium sulfate in treating people arriving in the Emergency Department with asthma attacks? Can it help some to avoid hospital admission? In this guest post, Dr Chris Cates looks at the latest evidence.
The full report of the large “3Mg trial” of intravenous or nebulised magnesium sulfate in adults with asthma exacerbations was published in April 2014. The authors concluded that they “were unable to demonstrate any clinically worthwhile benefit from magnesium sulphate in acute severe asthma”, and thereby questioned whether there was a place for using intravenous magnesium sulfate in adults with an asthma exacerbation who had not responded to the first line treatments of steroid tablets (on injections) in combination with nebulised salbutamol and ipratropium.
However, the confidence interval around their findings on hospital admission were too wide to rule out a beneficial effect of treatment with intravenous magnesium sulfate, and they did not combine the results of this new trial with the existing evidence from previous randomised trials. This is exactly what the authors have done in the recently published Cochrane review on this topic . When the results of the new trial are added to those of the studies that have gone before, overall the review showed a significant reduction in the chance of being admitted to hospital in those adults who were given intravenous magnesium sulfate compared to a placebo injection. In absolute terms, there was a reduction of seven hospital admissions for every 100 adults who were treated with magnesium sulfate. There was uncertainty due to the play of chance, meaning that we are confident that, for every 100 adults with acute asthma treated with intravenous magnesium, between two and 13 fewer adults would need admission to hospital.
As a double check, the results remained very similar when the reviewers excluded the results of studies that were not published in full, or were not protected by a double-blind design. They also looked to see if they could identify a difference between the effectiveness of intravenous magnesium sulfate in adults who had already been given nebulised ipratropium or those who had not, and for differences in the effect of magnesium sulfate according to how severe the person’s asthma attack was. They could not find any clear differences, but this does not mean that intravenous magnesium sulfate necessarily works just as well across all these circumstances, we just do not yet know!
In the randomised trials, intravenous magnesium sulfate was given as a single dose of 1.2 g or 2 g over 15 to 30 minutes. Used in this way the overall evidence showed that there were improvements in lung function and a reduction in the risk of hospital admission. Even though the recent trial was not conclusive, the sum of the evidence from all randomised trials does suggest benefit from intravenous magnesium sulfate on lung function and the risk of hospital admission, in adults with acute asthma exacerbations that have not resolved with current first line treatments.
1. Goodacre S, Cohen J, Bradburn M, et al. The 3Mg trial: a randomised controlled trial of intravenous or nebulised magnesium sulfate versus placebo in adults with acute severe asthma. Health Technol Assess 2014;18(22) doi: 10.3310/hta18220[published Online First: Epub Date]|.
2. Kew KM, Kirtchuk L, Michell CI. Intravenous magnesium sulfate for treating adults with acute asthma in the emergency department. Cochrane Database of Systematic Reviews 2014, Issue 5. Art. No.: CD010909. DOI: 10.1002/14651858.CD010909.pub2.