title: The effects of plasma and brain magnesium concentrations on lidocaine-induced seizures in the rat.
abstract: Lidocaine and MgSO4 are often coadministered to patients with pregnancy-induced hypertension. This study examined whether MgSO4 alters the lidocaine-seizure threshold in the rat and, if so, whether systemic MgSO4 administration is as effective as intracerebroventricular MgSO4 infusion. In Experiment 1, rats were administered 50% MgSO4 or 0.9% NaCl intravenously (IV) (20 microL/h) for 5 days. In Experiment 2, rats were administered 0.9% NaCl, 0.8% MgSO4, or 2.0% MgSO4 (10 microL/h) via intracerebroventricular infusion for 24 h. All rats then underwent continuous IV lidocaine infusion until onset of electroencephalographic seizures. 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 lidocaine required to induce seizures (MgSO4 = 19 +/- 2 mg/kg; saline = 23 +/- 5 mg/kg) nor brain [Mg2+] (MgSO4 = 794 +/- 17 micrograms/g; saline = 788 +/- 33 micrograms/g) were changed. In Experiment 2, intracerebroventricular MgSO4 increased both brain [Mg2+] (2% MgSO4 = 923 +/- 79 micrograms/g; saline = 788 +/- 35 micrograms/g) and the lidocaine seizure dose (2% MgSO4 = 39 +/- 7 mg/kg; saline = 26 +/- 3 mg/kg). Although intracerebroventricular administration of MgSO4 produces an anticonvulsant effect, chronic hypermagnesemia does not alter whole brain [Mg2+] and therefore offers no protection from lidocaine-induced seizures in this model.
authors.affiliation: Department of Anesthesiology, Yonsei University, Seoul, Korea.
authors.forename: Y J
authors.initials: YJ
authors.lastname: Kim
authors.forename: C
authors.initials: C
authors.lastname: McFarlane
authors.forename: D S
authors.initials: DS
authors.lastname: Warner
authors.forename: M T
authors.initials: MT
authors.lastname: Baker
authors.forename: W W
authors.initials: WW
authors.lastname: Choi
authors.forename: F
authors.initials: F
authors.lastname: Dexter
mesh_terms: D000818:Animals; D000927:Anticonvulsants / Q000008:administration & dosage / Q000494:pharmacology; D001794:Blood Pressure; D001831:Body Temperature; D001921:Brain / Q000378:metabolism*; D002245:Carbon Dioxide / Q000097:blood; D003292:Convulsants / Q000008:administration & dosage / Q000009:adverse effects*; D004569:Electroencephalography / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007262:Infusions, Intravenous; D007276:Injections, Intraventricular; D008012:Lidocaine / Q000008:administration & dosage / Q000009:adverse effects*; D008274:Magnesium / Q000032:analysis* / Q000097:blood*; D008278:Magnesium Sulfate / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology; D008297:Male; D010100:Oxygen / Q000097:blood; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012640:Seizures / Q000097:blood / Q000139:chemically induced* / Q000378:metabolism
chemical_list: D000927:Anticonvulsants; D003292:Convulsants; D002245:Carbon Dioxide; D008278:Magnesium Sulfate; D008012:Lidocaine; D008274:Magnesium; D010100:Oxygen