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

Summary.

 Background: 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.

 Methods: 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/dayly; group B (n=6) a continuous infusion of 30 mmol/dayly; and group C (n=5) a continuous infusion of 64 mmol/dayly. 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.

 Findings: 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.

 Interpretation: 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.