Background: The benefits of supplemental administration of intravenous magnesium in patients with ST-elevation myocardial infarction (STEMI) are controversial. Despite promising results from work in animals and the ready availability of this simple, inexpensive treatment, conflicting results have been reported in clinical trials. Our aim was to compare short-term mortality in patients with STEMI who received either intravenous magnesium sulphate or placebo.
Methods: We did a randomised, double-blind trial in 6213 patients with acute STEMI who were assigned a 2 g intravenous bolus of magnesium sulphate administered over 15 min, followed by a 17 g infusion of magnesium sulphate over 24 h (n=3113), or matching placebo (n=3100). Our primary endpoint was 30-day all-cause mortality. At randomisation, patients were stratified by their eligibility for reperfusion therapy. The first stratum included patients who were aged 65 years or older and eligible for reperfusion therapy, and the second stratum included patients of any age who were not eligible for reperfusion therapy. Analysis was by intention-to-treat.
Findings: At 30 days, 475 (15.3%) patients in the magnesium group and 472 (15.2%) in the placebo group had died (odds ratio 1.0, 95% CI 0.9-1.2, p=0.96). No benefit or harm of magnesium was observed in eight prespecified subgroup analyses of patients and in 15 additional exploratory subgroup analyses. After adjustment for factors shown to effect mortality risk in a multivariate regression model, no benefit of magnesium was observed (1.0, 0.8-1.1, p=0.53).
Interpretation: Early administration of magnesium in high-risk patients with STEMI has no effect on 30-day mortality. In view of the totality of the available evidence, in current coronary care practice there is no indication for the routine administration of intravenous magnesium in patients with STEMI.