• T Coats and M Braidburn.
• Department of Emergency Medicine, Royal Infirmary of Edinburgh, Edinburgh, United Kingdom.
• Emerg Med J. 2013 Oct 1;30(10):866.

Objectives & BackgroundPrevious studies suggest intravenous or nebulised magnesium sulphate may improve respiratory function in patients with acute asthma. We aimed to determine whether intravenous or nebulised MgSO4 improve symptoms of breathlessness and reduce the need for hospital admission in adults with severe acute asthma.MethodsIn a double-blind, placebo-controlled trial, we enrolled adults with severe acute asthma at emergency departments of 34 UK hospitals. We excluded patients with life-threatening features. Allocated participants received IV MgSO4 (2 g in 20 min) or nebulised MgSO4 (3×500 mg doses in 1 h)+standard therapy, or placebo+standard therapy. We assessed two primary outcome measures in all participants according to treatment group: the proportion of patients admitted to hospital within 7 days and breathlessness measured on a 100 mm VAS in the 2 h after initiation of treatment. We adjusted for multiple testing. Study registration no: ISRCTN04417063.Results1109 patients were recruited (Jul 2008 to Jun 2012). 261 (79%) of 332 patients allocated nebulised MgSO4 were admitted to hospital, as were 285 (72%) of 394 patients allocated intravenous MgSO4 and 281 (78%) of 358 controls. Breathlessness was assessed in 296 (89%) patients allocated nebulised MgSO4, 357 (91%) patients allocated intravenous MgSO4, and 323 (90%) controls. Rates of hospital admission did not differ between patients treated with either form of MgSO4 compared with controls or each other. Change in VAS breathlessness did not differ between active treatments and control, but change in VAS was greater for patients in the intravenous MgSO4 group than the nebulised MgSO4 group (5.1 mm, 0.8 to 9.4; p=0.019). Intravenous or nebulised MgSO4 did not significantly decrease rates of hospital admission and breathlessness compared with placebo: intravenous MgSO4 was associated with an odds ratio of 0.73 (95% CI 0.51 to 1.04; p=0.083) for hospital admission and a change in VAS breathlessness of 2.6 mm (-1.6 to 6.8; p=0.231) compared with placebo; nebulised MgSO4 was associated with an odds ratio of 0.96 (0.65 to 1.40; p=0.819) for hospital admission and a change in VAS breathlessness of -2.6 mm (-7.0 to 1.8; p=0.253) compared with placebo.ConclusionThese data suggest nebulised MgSO4 has no role in the management of severe acute asthma in adults and at best suggest only a limited role for intravenous MgSO4 in the ED.

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