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IV magnesium may do more harm than good in subarachnoid hemorrhage

Reuters Health • The Doctor's Channel Daily Newscast

NEW YORK (Reuters Health) – Intravenous magnesium sulfate infusions may not help patients with acute aneurysmal subarachnoid hemorrhage, according to a study published in the August issue of Stroke, released online June 10.

In fact, researchers from Hong Kong and New Zealand found, high magnesium plasma concentrations were associated with worse neurologic outcomes. The findings conflict with earlier preliminary results that had suggested hypomagnesemia after subarachnoid hemorrhage could lead to poor outcomes.

Dr. George K. C. Wong, of the Chinese University of Hong Kong, and colleagues analyzed data from a recent randomized, double-blinded phase III trial that enrolled 327 adult patients. Of these, 169 received magnesium sulfate (80 mmol in 500 mL saline daily) while 158 were given a placebo infusion (500 mL normal saline daily) for up to 14 days after a diagnosis of acute aneurysmal subarachnoid hemorrhage. Infusion began after an average of 31.7 hours from ictus.

The magnesium dose was adjusted to achieve a plasma concentration between 2 mmol/L and 2.5 mmol/L. Patients also received nimodipine.

To test the effects of magnesium, the researchers compared plasma levels with stratified neurologic outcomes, including the Extended Glasgow Scale (primary outcome, evaluated at 6 months), the modified Rankin Scale (evaluated at 6 months), the Barthel Index, and delayed ischemic neurologic deficit.

In patients receiving magnesium, higher plasma magnesium levels were associated with worse scores (p<0.01) for all outcomes except delayed ischemic neurologic deficit. In patients receiving only saline, worse Extended Glasgow Outcome Scale scores and delayed ischemic neurologic deficits were seen in those with higher plasma magnesium levels.

On multivariate analysis, a mean plasma magnesium concentration greater than 1.82 mmol/L in the treatment group significantly lowered the odds of a favorable outcome on the Extended Glasgow Outcome Scale (scores 5-8, odds ratio 0.3) and modified Rankin Scale (scores 0-2, OR 0.3).

Similarly, in the control group, a plasma magnesium level greater than 0.89 mmol/L significantly lowered the odds of a favorable outcome on the Extended Glasgow Outcome Scale, modified Rankin Scale, and Barthel Index.