Delayed ischemic neurological deficit or clinical vasospasm remained a major 
cause for delayed neurological morbidity and mortality for patients with 
aneurysmal subarachnoid hemorrhage (SAH). Magnesium is a cerebral vasodilator. 
In experimental model of drug or SAH-induced vasospasm, magnesium blocks 
voltage-dependent calcium channels and reverses cerebral vasoconstriction. 
Furthermore, its antagonistic action on N-methyl-D-aspartate receptor in the 
brain prevents glutamate stimulation and decreases calcium influx during 
ischemic injury. Clinically, the protective effect of magnesium has also been 
found useful in women with preeclampsia, a condition thought to be due to 
cerebral vasospasm. Initial experimental result in human was found to safe and 
effective as compared to historical data. In our pilot study, 60 patients were 
randomly allocated to receive either magnesium sulfate infusion 80 mmol/day or 
saline infusion for 14 days. The incidence of symptomatic vasospasm decreased 
from 13/30(43%) in the saline group to 7/30(23%) in the patients receiving 
magnesium sulfate infusion, p = 0.10, odds ratio 0.398, 95% CI 0.131-1.211. 
Favorable outcome (Good recovery and moderate disability, as defined by Glasgow 
Outcome Scale) was achieved in 20 of 30 (67%) patients receiving magnesium 
sulfate infusion and 16 of 30 (53%) patients receiving placebo treatment, p = 
0.292, odds ratio 1.750, 95% CI 0.616-4.974.From literature review, a total of 
441 patients from four studies (including ours) were grouped for analysis. Using 
random effects model (Mantel-Haenszel, Robins-Breslow-Greenland), the pooled 
odds ratio for symptomatic vasospasm or delayed cerebral ischemia is, 0.620, 95% 
CI 0.389-0.987, statistically significant. Similarly, the pooled odds ratio for 
favorable outcome is 1.598, 95% CI 1.074-2.377, statistically significant. There 
are two multi-center phase III studies (IMASH and MASH2) being carried out to 
assess the clinical effects, in which IMASH has finished data collection on 30th 
June 2009.