Correspondence to ‘dose evaluation for long‐term magnesium treatment in aneurysmal subarachnoid haemorrhage’

To the editor, van Norden et al. (1) evaluated the dose required for long-term magnesium treatment in aneurysmal subarachnoid haemorrhage. We had been running a similar multicentre trial since 2002 and we wish to share our points of view on the dose regimen (2). The optimal plasma magnesium concentration for neuroprotection remains uncertain at this moment in time. In this regard, van Norden et al. (1) referred to an experiment in rats after transient global ischemia. They showed that the optimal plasma magnesium concentration was about 1Æ43 mmol/L (3). However, a more recent study suggested that a higher dose of magnesium is required for neuroprotection (4). In this study, a continuous infusion of magnesium sulphate (MgSO4) to maintain a plasma magnesium concentration between 2 and 3 mmol/L appeared to produce maximal protection against transient focal ischemia. We are currently targeting a plasma magnesium concentration twice the baseline values and <2Æ5 mmol/L (2). This is in keeping with the results of the more recent rat experiment (4) and should avoid significant side effects (1). Our protocol is to start off a bolus dose of MgSO4, 20 mmol and is followed by an infusion of MgSO4 of about 80 mmol/day. The infusion rate is adjusted according to the results of plasma magnesium concentration. In our pilot study, 74% of patients did not require further dose adjustment. The median (range) plasma magnesium concentration was 1Æ89 mmol/L (1Æ44)2Æ33). There were no significant side effects.