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

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/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. 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.