Yj. Kim et al., THE EFFECTS OF PLASMA AND BRAIN MAGNESIUM CONCENTRATIONS ON LIDOCAINE-INDUCED SEIZURES IN THE RAT, Anesthesia and analgesia, 83(6), 1996, pp. 1223-1228
Lidocaine and MgSO4 are often coadministered to patients with pregnanc
y-induced hypertension. This study examined whether MgSO4 alters the l
idocaine-seizure threshold in the rat and, if so, whether systemic MgS
O, administration is as effective as intracerebroventricular MgSO4 inf
usion. In Experiment 1, rats were administered 50% MgSO4 or 0.9% NaCl
intravenously (IV) (20 mu L/h) for 5 days. In Experiment 2, rats were
administered 0.9% NaCl, 0.8% MgSO4, or 2.0% MgSO4 (10 mu L/h) via intr
acerebroventricular infusion for 24 h. All rats then underwent continu
ous IV lidocaine infusion until onset of electroencephalographic seizu
res. In Experiment 1, plasma [Mg2+] was greater in the MgSO4 group (5.
1 +/- 1.5 mg/dL vs 1.8 +/- 0.3 mg/dL) but neither the dose of lidocain
e required to induce seizures (MgSO4 = 19 +/- 2 mg/kg; saline = 23 +/-
5 mg/kg) nor brain [Mg2+] (MgSO4 = 794 +/- 17 mu g/g; saline = 788 +/
- 33 mu g/g) were changed. In Experiment 2, intracerebroventricular Mg
SO, increased both brain [Mg2+] (2% MgSO4 = 923 +/- 79 mu g/g; saline
= 788 +/- 35 mu g/g) and the lidocaine seizure dose (2% MgSO4 = 39 +/-
7 mg/kg; saline = 26 +/- 3 mg/kg). Although intracerebroventricular a
dministration of MgSO4 produces an anticonvulsant effect, chronic hype
rmagnesemia does not alter whole brain [Mg2+] and therefore offers no
protection from lidocaine-induced seizures in this model.