BACKGROUND: Magnesium is a neuroprotective agent that might prevent or reverse 
delayed cerebral ischaemia after aneurysmal subarachnoid haemorrhage (SAH). We 
are presently running a randomized, placebo-controlled, double blind trial with 
magnesium sulphate (64 mmol/day intravenously). We studied whether this 
treatment regime resulted in our target serum magnesium levels of 1.0-2.0 
mmol/L.
METHODS: Magnesium sulphate was administered intravenously as soon as possible 
after admission and continued until 14 days after occlusion of the aneurysm. 
Serum magnesium measurements were done at baseline and at least every 2 days 
during administration of trial medication. For comparison we used the serum 
magnesium levels of the placebo-treated patients.
RESULTS: Magnesium therapy was begun in 94 patients. The mean magnesium level in 
the treatment period was 1.47 +/- 0.32 mmol/L. In 81 patients serum magnesium 
stayed within target levels during the entire treatment period. One patient had 
a serum magnesium level below 1.0 mmol/L (0.91 mmol/L) in a single measurement 
and 10 patients had serum magnesium levels above 2.0 mmol/L at one or more 
measurements. In six patients magnesium therapy was discontinued: in three 
because of nausea, headache, or both in combination with serum magnesium levels 
above 2.0 mmol/L and in the other three because of hypotension, phlebitis and 
renal failure.
CONCLUSIONS: With an intravenous dosage schedule of 64 mmol magnesium sulphate a 
day, serum magnesium levels of 1.0-2.0 mmol/L can easily be maintained without 
severe side effects for an extended period in a vast majority of patients with 
SAH.