Magnesium therapy after aneurysmal subarachnoid haemorrhage a dose-finding study for long term treatment

Magnesium is a neuroprotective agent which might prevent or reverse delayed cerebral ischemia (DCI) after aneurysmal subarachnoid haemorrhage (SAH). Although the dosage for short-term magnesium therapy is well established, there is lack of knowledge on the dosage for extended use of magnesium. Our aim was to find a dosage schedule of magnesium sulphate to maintain a serum magnesium level of 1.0-2.0 mmol/L for 14 days to cover the period of DCI.

We prospectively studied 14 patients admitted within 48 hours after aneurysmal subarachnoid haemorrhage (SAH) to our hospital. Magnesium sulphate was administrated intravenously for 14 days, using 3 different dosage schedules. Group A (n=3) received a bolus injection of 16 mmol magnesium sulphate followed by a continuous infusion of 16 mmol/daily; group B (n=6) a continuous infusion of 30 mmol/daily; and group C (n=5) a continuous infusion of 64 mmol/daily. Serum magnesium was measured at least every two days and all patients were under continuous observation during magnesium treatment. Renal magnesium excretion was measured only in group C.

In treatment group A the mean serum magnesium level during treatment was 1.03+/-0.14 (range 0.82-1.34) mmol/L, in group B 1.10+/-0.15 (range 0.87-1.43) mmol/L, and in group C 1.38+/-0.18 (range 1.11-1.98) mmol/L. The renal magnesium excretion in group C was equal to the administrated doses within 48 hours after treatment had started. All patients in group A reported a flushing sensation during the bolus injection; no other side effects were noted.

With a continuous intravenous dosage of 64 mmol/L per day, serum magnesium levels maintained within the range of 1.0-2.0 mmol/L for 14 days.