Dose evaluation for long-term magnesium treatment in aneurysmal subarachnoid haemorrhage

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.

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.

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.

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.