BACKGROUND AND PURPOSE: Conflicting data have been obtained on optimal plasma 
magnesium concentrations for clinical outcomes in patients with aneurysmal 
subarachnoid hemorrhage.
METHODS: Adults (aged 18 years or older) who had acute aneurysmal subarachnoid 
hemorrhage diagnosed were randomly assigned to receive either an intravenous 
MgSO(4) infusion (80 mmol in 500 mL normal saline per day) or a placebo (500 mL 
normal saline per day) for up to 14 days. Post hoc multivariable binary logistic 
regression analyses were performed by dividing mean plasma magnesium 
concentrations into 4 quartiles according to treatment group and then comparing 
with the lowest quartiles.
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.