title: Cerebral and plasma kinetics of a high dose of midazolam and correlations with its respiratory effects in rats.
abstract: Benzodiazepine poisoning causes coma and respiratory depression. Our objective was to determine whether, and to what extent, arterial blood gas disturbances correlated with blood or cerebral kinetics of midazolam. A 160 mgkg(-1) single dose of midazolam was infused intravenously over 20 min in catheterized male Sprague-Dawley rats. Midazolam kinetics was simultaneously determined in plasma and brain using striatal microdialysis. Midazolam concentrations were measured using a high-performance liquid chromatographic assay with ultraviolet detection. Midazolam (160 mgkg(-1)) reproducibly induced deep coma with respiratory acidosis. Plasma midazolam kinetics was well described by a bi-exponential model, with an elimination half-life of 6.4+/-1.8 h. The striatal dialysate concentration peaked at 50.0+/-8.9 min after the end of infusion, with a significant delay to peak concentration compared to plasma. Respiratory depression, assessed by the elevation in PaCO2, was more closely correlated with midazolam striatal dialysate rather than plasma kinetics. These results suggest a central mechanism for midazolam respiratory effects at toxic doses in rats. In conclusion, our study showed a delayed onset in peak PaCO2 and pH effects after the slow infusion of a toxic dose of midazolam in rats. The effects on arterial blood gases were better correlated with midazolam striatal concentrations than with plasma concentrations. This study may contribute to better understanding of benzodiazepine-induced respiratory depression in poisonings.
authors.affiliation: INSERM U705, CNRS, UMR 7157-Université Paris VII, Hôpital Fernand Widal, Paris, France. bruno-megarbane@wanadoo.fr
authors.forename: Bruno
authors.initials: B
authors.lastname: Megarbane
authors.forename: Nicolas
authors.initials: N
authors.lastname: Lesguillons
authors.forename: Martine
authors.initials: M
authors.lastname: Galliot-Guilley
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Borron
authors.forename: Hervé
authors.initials: H
authors.lastname: Trout
authors.forename: Xavier
authors.initials: X
authors.lastname: Declèves
authors.forename: Patricia
authors.initials: P
authors.lastname: Risède
authors.forename: Claire
authors.initials: C
authors.lastname: Monier
authors.forename: Gabrielle
authors.initials: G
authors.lastname: Boschi
authors.forename: Frédéric J
authors.initials: FJ
authors.lastname: Baud
mesh_terms: D000138:Acidosis / Q000139:chemically induced / Q000503:physiopathology; D000818:Animals; D001639:Bicarbonates / Q000097:blood; D001784:Blood Gas Analysis; D001921:Brain / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D006207:Half-Life; D006993:Hypnotics and Sedatives / Q000097:blood / Q000493:pharmacokinetics*; D008297:Male; D017551:Microdialysis; D008874:Midazolam / Q000097:blood / Q000493:pharmacokinetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015656:Respiratory Mechanics / Q000187:drug effects*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D001639:Bicarbonates; D006993:Hypnotics and Sedatives; D008874:Midazolam