RESULTS: The worst clinical outcomes at 6 months were seen in MgSO(4) group patients, with mean plasma magnesium concentrations in the fourth quartile, and in placebo group patients, with mean such concentrations in the third and fourth quartiles. CONCLUSIONS: No evidence was found to suggest that a higher mean plasma magnesium concentration improves clinical outcomes. On the contrary, we found an association between high plasma magnesium concentration and worse clinical outcomes.