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ORIGINAL ARTICLES |
Medical Care Research Unit, University of Sheffield, Sheffield, UK
Correspondence to:
Professor S Goodacre, Medical Care Research Unit, University of Sheffield, Regent Court, 30 Regent Street, Sheffield, S1 4DA, UK; s.goodacre{at}sheffield.ac.uk
Accepted 30 August 2007
| ABSTRACT |
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Methods: We undertook a systematic review and meta-analysis of randomised and quasi-randomised trials of intravenous or nebulised magnesium sulphate in acute asthma. Trials were identified by searches of the electronic literature, relevant journal websites and conference proceedings, and contact with authors and experts. Data were pooled using random effects meta-analysis of the relative risk (RR) of hospital admission and the standardised mean difference (SMD) in pulmonary function.
Results: 24 studies (15 intravenous, 9 nebulised) incorporating 1669 patients were included. Intravenous treatment was associated in adults with weak evidence of an effect upon respiratory function (SMD 0.25, 95% confidence interval (CI) –0.01 to 0.51; p = 0.05), but no significant effect upon hospital admission (RR 0.87, 95% CI 0.70 to 1.08; p = 0.22), and in children with a significant effect upon respiratory function (SMD 1.94, 95% CI 0.80 to 3.08; p<0.001) and hospital admission (RR 0.70, 95% CI 0.54 to 0.90; p = 0.005). Nebulised treatment was associated in adults with weak evidence of an effect upon respiratory function (SMD 0.17, 95% CI –0.02 to 0.36; p = 0.09), and hospital admission (RR 0.68, 95% CI 0.46 to 1.02; p = 0.06), and in children with no significant effect upon respiratory function (SMD –0.26, 95% CI –1.49 to 0.98; p = 0.69) or hospital admission (RR 2.0, 95% CI 0.19 to 20.93; p = 0.56).
Conclusion: Intravenous magnesium sulphate appears to be an effective treatment in children. Further trials are needed of intravenous and nebulised magnesium sulphate in adults and nebulised magnesium sulphate in children.
Abbreviations: BTS, British Thoracic Society; CI, confidence interval; RR, relative risk; SIGN, Scottish Intercollegiate Guidelines Network; SMD, standardised mean difference
Asthma affects 5.2 million people in the UK, including 1.1 million children,1 and is responsible for around 60 000 hospital admissions per year.2 Guidelines from the British Thoracic Society (BTS) and Scottish Intercollegiate Guidelines Network (SIGN) advise a stepwise approach to the management of exacerbations.3 Initially all patients should receive oxygen; nebulised β2-agonists; nebulised anticholinergic agent and corticosteroids. However, bronchodilators act within minutes whereas corticosteroids require hours. This discrepancy suggests a role for magnesium as an alternative treatment option in patients resistant to standard therapy. Magnesiums pharmacological action is based upon its ability to inhibit the release of calcium from vesicles in the sarcoplasmic reticulum, resulting in bronchial smooth muscle relaxation.4
Magnesium has been evaluated in both the intravenous and nebulised dosage form. The aerosolised route offers the advantage of a quick onset of action and lower incidence of side effects. Its disadvantages include a lower percentage of drug being delivered to the site of action and the patient requiring some respiratory effort to maximise its effectiveness. The intravenous route provides direct access to the venous system, allowing the delivery of high drug concentrations. The disadvantages include a cannula being sited and the drug being administered over 20 min.
Four meta-analyses have compared intravenous magnesium sulphate to placebo.5–8 Rowe et al5 identified five adult and two paediatric trials and concluded that magnesium sulphate therapy did not significantly improve peak expiratory flow rate or reduce admission to hospital, but subgroup analysis suggested that in trials of severe asthma, magnesium sulphate treatment was effective. Alter et al6 identified seven adult and two paediatric trials and found that magnesium sulphate was associated with a significant improvement in spirometric airway function by 16% of a standard deviation, but concluded that the clinical significance of this effect was uncertain. Rodrigo et al7 identified five adult trials and found no significant effect from magnesium sulphate upon pulmonary function or hospital admissions. Cheuk et al8 undertook a meta-analysis of five trials in children and concluded that intravenous magnesium sulphate was effective in reducing hospital admissions, and improving pulmonary function tests and clinical symptoms. Two reviews have compared nebulised magnesium sulphate to placebo.9 10 Both included six trials and concluded that current evidence could not clearly determine the role of nebulised magnesium sulphate in acute asthma.
The most recent (2007) BTS/SIGN guidelines state that a single dose of intravenous magnesium sulphate has been shown to be safe and effective in adults, and should be considered in adults with life threatening features or acute severe asthma that has not responded to inhaled bronchodilator treatment. The guidelines for children are more equivocal, suggesting that intravenous magnesium sulphate is safe but its place in management is not yet established. Nebulised magnesium sulphate is not discussed in either adults or children.
The evidence base for intravenous and nebulised magnesium sulphate has increased since these meta-analyses were published, with the recent publication of additional randomised trials. It is also apparent that magnesium sulphate may have a different role in adults and children. We therefore aimed to undertake a systematic review and meta-analysis of both intravenous and nebulised magnesium sulphate to determine their role in adults and children with acute asthma. Our specific objectives were to estimate the effect of each treatment upon pulmonary function and hospital admission.
| METHODS |
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The search terms "asthma" OR "wheeze" AND "magnes" were used to search the following databases: Cochrane Airways Review Group asthma register; Cochrane Clinical Trials Registry; Medline (1966-present); Medline in process (1966–present); EMBASE (1988–present); CINAHL (1982–present); AMED (1985–present); Research Registers of ongoing trials (MetaRegister of Current Controlled Trials (controlled-trials.com); National Research Register (NRR) and Centerwatch.com); Conference Papers Index; Web of Science; Dissertation Abstracts and the World Wide Web using the Google search engine.
We searched the websites of the following relevant journals: Emergency Medicine Journal; Academic Emergency Medicine; Thorax; Chest; European Respiratory Journal; Internet Scientific Journals/Journal Medical Internet Research (Emergency Medicine; Asthma, Allergy, Immunology; Pulmonary Medicine); Journal of Allergy and Clinical Immunology; Lancet; European Journal of Emergency Medicine; Annals of Emergency Medicine; American Journal Emergency Medicine; American Journal Respiratory and Critical Care Medicine; Journal of the American Medical Association; Journal of Asthma; British Medical Journal; Achives of Internal Medicine; Journal of Emergency Medicine. We also searched relevant conference proceedings for the previous 5 years for relevant trials: Society for Academic Emergency Medicine Annual Conference; Annual Thoracic Society International Conference; Annual Congress of European Respiratory Society; American College of Chest Physicians.
The reference lists of all articles selected were reviewed for relevant studies. The primary authors of included studies were contacted (where possible, determined by availability of an email address) for information on additional trials, both published and unpublished. Finally, clinicians, collaborators, colleagues and trialists were contacted to identify additional potentially relevant studies.
A single reviewer (SM) scanned titles and abstracts, searched journals, and contacted experts, and selected potentially relevant articles for review. When possible we retrieved the full version of selected articles. Two independent reviewers (SM and SG) then reviewed potentially relevant articles and selected definitely relevant articles for inclusion. Each reviewer also independently assessed the quality of each included study using the five point Jadad score. This scale is used to assess randomisation, double blinding and withdrawals/dropouts. All trials were scored using a scale of 1 to 5 (score of 5 being the highest).
The following data were extracted from each study: design (method of randomisation, withdrawals/dropouts, inclusion and exclusion criteria); participants (age, gender, severity of asthma); interventions (route of administration, dose, timing and duration of therapy, co-interventions); control (agents and doses used); outcomes (types of outcome measures and the timing of their measurements, hospital admission rates and side effects) and results. Unpublished data were requested from the primary author by email.
Data were analysed using RevMan statistical software (version 4.0). Since a variety of different pulmonary function measures were used in the trials, these measures were analysed as a standardised mean difference (SMD). Hospital admission was analysed as a relative risk. Both outcomes were pooled using a random effects model. Initially all studies were analysed together, then studies of adults and children were analysed separately.
| RESULTS |
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= 0.83).
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| DISCUSSION |
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Most previous meta-analyses have analysed adults and children together. Our analysis suggests that this may be inappropriate, particularly for intravenous magnesium sulphate, because there appears to be a clear difference in effectiveness between these two patient groups. It is not clear why effectiveness should differ between adults and children. Possible explanations are that children may have a greater element of reversibility to their acute asthma, or the use of weight adjusted dosing in children allows for a more appropriate dose of intravenous magnesium.
Our analysis has a number of potential limitations. Firstly, we may have failed to identify unpublished studies. We undertook a comprehensive literature search, including searches of conference abstracts, and identified three unpublished studies that were included in the review. Nevertheless we will not have identified studies that were neither presented nor published in any form. Secondly, we identified but were unable to include three potentially relevant studies because of limitations in their reporting. Thirdly, heterogeneity with respect to the exclusion criteria, treatment interventions and outcome measures may limit the appropriateness of pooling data. Of particular relevance and concern is the fact that the studies varied in whether patients with existing pulmonary pathology (such as chronic obstructive pulmonary disease) were excluded from the study. This is particularly significant as it is thought that patients with "pure" asthma are more likely to respond to magnesium treatment. Fourthly, most of the included studies were small and not powered to detect potentially important differences in hospital admission rates. Even after pooling these data we cannot exclude a potentially important effect from intravenous or nebulised magnesium sulphate in adults. Finally, we did not identify any studies that directly compared intravenous to nebulised magnesium sulphate.
Our analysis suggests that the revised (2007) BTS/SIGN guidelines are not entirely consistent with the current evidence. The guidelines suggest a clear role for intravenous magnesium sulphate in adults, but not children, and do not consider nebulised magnesium sulphate. In contrast, our analysis suggests that intravenous magnesium sulphate is an effective treatment for acute severe asthma in children, but has an uncertain role in adults. Nebulised and intravenous magnesium sulphate appear to be associated with similar estimates of effectiveness in adults, ranging from little or no effect to a substantial, worthwhile effect. Thus we can neither clearly state nor rule out a useful role for either nebulised of intravenous magnesium sulphate in adults.
The implications of our analysis are that intravenous magnesium sulphate should be standard treatment for children with acute severe asthma that has not responded to initial treatment, while the role of nebulised magnesium sulphate in children and the roles of both nebulised and intravenous magnesium sulphate in adults require further investigation. Given the low risk of serious side effects from magnesium sulphate it would seem reasonable to use intravenous magnesium sulphate in adults with life threatening features, in whom any potential benefit would justify the risks of treatment. Meanwhile, a large randomised trial is required to compare nebulised and intravenous magnesium sulphate to each other, and to placebo, in adults with acute severe asthma, to determine whether magnesium sulphate can improve symptoms and reduce hospital admissions. Further studies of nebulised magnesium sulphate in children are currently in progress.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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| REFERENCES |
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