What is the role of IV magnesium as adjunctive therapy in acute MI?

Meta-analyses of several small clinical trials of intravenous magnesium in acute myocardial infarction (MI) suggested that this therapy may reduce mortality. The Second Leicester Intravenous Magnesium Intervention Trial (LIMIT-2) also showed that early administration of magnesium in patients With suspected MI decreased all-cause mortality, both at 28 days and over long-term Follow-up. In contrast, the Fourth International Study of Infarct Survival (ISIS-4), in which magnesium was begun 1 hour after the initiation of thrombolytic therapy and aspirin, found no favorable effect of magnesium on mortality or the incidence of serious arrhythmias. These discrepant results may be due to the delay in administering magnesium in ISIS-4, or to the fact that the amount of magnesium given and/or the duration of infusion were less than optimal. Further studies aimed at resolving these issues should definitively establish whether or not magnesium therapy affords any benefit in acute MI.