Intravenous magnesium sulfate does not increase ventricular CSF ionized magnesium concentration of patients with intracranial hypertension

Magnesium sulfate has attracted interest as a potential neuroprotectant but passage of magnesium ion into the central nervous system has not been well documented. For this study, we quantified plasma and cerebrospinal fluid ( CSF) ionized magnesium concentration after systemic magnesium sulfate infus ion in patients with intracranial hypertension, Patients (N = 9) received a n intravenous infusion of 5 g/20 mmol magnesium sulfate (125 mL of a 4% wt/ vol solution) over 30 minutes. Before and after dosing, CSF (from an indwel ling ventricular catheter) and blood samples were collected at hourly inter vals. Ionized magnesium concentration in all samples was determined using a n electrolyte analyzer. Baseline plasma and CSF ionized magnesium concentra tions were 0.58 +/- 0.05 and 0.82 +/- 0.06 mmol/L, respectively. Intravenou s magnesium sulfate infusion significantly increased plasma ionized magnesi um concentration (peak, 0.89 +/- 0.11 mmol/L), but CSF magnesium levels did not change during the 4-hour study. Systemic administration of magnesium s ulfate failed to increase CSF ionized magnesium concentration in patients W ith intracranial hypertension despite increasing plasma magnesium levels by > 50%.