Two hundred-eighty-three patients (mean age, 55 years) with subarachnoid hemorrhage due to an aneurysm were randomly assigned, within 4 days (mean, 35 hours) of the event, to receive, in double-blind fashion, intravenous magnesium sulfate (Mg) or placebo (normal saline). Mg was given as a continuous infusion at a dose of 64 mmol/day, and was continued until 14 days after occlusion of the aneurysm. The primary outcome measure was the incidence of delayed cerebral ischemia (defined as the occurrence of a new hypodense lesion on computed tomography compatible with clinical features of delayed cerebral ischemia). Compared with placebo, Mg treatment reduced the risk of delayed cerebral ischemia by 34% (relative risk = 0.66; 95% CI, 0.38-1.14). The number-needed-to-treat was 14, meaning that for every 14 patients treated, 1 episode of delayed cerebral ischemia would be prevented. After 3 months, Mg supplementation reduced the risk for poor outcome by 23%, a reduction that was of borderline statistical significance. Eighteen patients in the Mg group had an excellent outcome, as compared with 6 in the placebo group (p < 0.05).

Comment: Subarachnoid hemorrhage occurs at a young age and often has a poor outcome. Death or dependence occurs in approximately 70% of patients, and is attributed to delayed cerebral ischemia in approximately one-third of patients with a poor outcome. Hypomagnesemia occurs in more then 50% of patients with subarachnoid hemorrhage, and is related to the occurrence of delayed cerebral ischemia and poor outcome after 3 months. Magnesium reverses cerebral vasospasm and reduces infarct volume after experimental subarachnoid hemorrhage in rats. The results of the present study demonstrate that intravenous magnesium can reduce the incidence of delayed cerebral ischemia and subsequent poor outcome in patients with subarachnoid hemorrhage due to an aneurysm.

van den Bergh WM, et al. Magnesium sulfate in aneurysmal subarachnoid hemorrhage: a randomized controlled trial. Stroke 2005;36:1011-1015.