title: Mechanisms of tramadol-related neurotoxicity in the rat: Does diazepam/tramadol combination play a worsening role in overdose?
abstract: Poisoning with opioid analgesics including tramadol represents a challenge. Tramadol may induce respiratory depression, seizures and serotonin syndrome, possibly worsened when in combination to benzodiazepines. Our objectives were to investigate tramadol-related neurotoxicity, consequences of diazepam/tramadol combination, and mechanisms of drug-drug interactions in rats. Median lethal-doses were determined using Dixon-Bruce's up-and-down method. Sedation, seizures, electroencephalography and plethysmography parameters were studied. Concentrations of tramadol and its metabolites were measured using liquid-chromatography-high-resolution-mass-spectrometry. Plasma, platelet and brain monoamines were measured using liquid-chromatography coupled to fluorimetry. Median lethal-doses of tramadol and diazepam/tramadol combination did not significantly differ, although time-to-death was longer with combination (P=0.04). Tramadol induced dose-dependent sedation (P<0.05), early-onset seizures (P<0.001) and increase in inspiratory (P<0.01) and expiratory times (P<0.05). The diazepam/tramadol combination abolished seizures but significantly enhanced sedation (P<0.01) and respiratory depression (P<0.05) by reducing tidal volume (P<0.05) in addition to tramadol-related increase in respiratory times, suggesting a pharmacodynamic mechanism of interaction. Plasma M1 and M5 metabolites were mildly increased, contributing additionally to tramadol-related respiratory depression. Tramadol-induced early-onset increase in brain concentrations of serotonin and norepinephrine was not significantly altered by the diazepam/tramadol combination. Interestingly neither pretreatment with cyproheptadine (a serotonin-receptor antagonist) nor a benserazide/5-hydroxytryptophane combination (enhancing brain serotonin) reduced tramadol-induced seizures. Our study shows that diazepam/tramadol combination does not worsen tramadol-induced fatality risk but alters its toxicity pattern with enhanced respiratory depression but abolished seizures. Drug-drug interaction is mainly pharmacodynamic but increased plasma M1 and M5 metabolites may also contribute to enhancing respiratory depression. Tramadol-induced seizures are independent of brain serotonin.
authors.affiliation: Inserm, U1144, Paris, France; UMR-S 1144, Paris-Descartes University, Paris, France; UMR-S 1144, Paris-Diderot University, Paris, France. Electronic address: camille.lagard@gmail.com.
authors.forename: Camille
authors.initials: C
authors.lastname: Lagard
authors.affiliation: Inserm, U1144, Paris, France; UMR-S 1144, Paris-Descartes University, Paris, France; UMR-S 1144, Paris-Diderot University, Paris, France. Electronic address: luciechevillard@gmail.com.
authors.forename: Lucie
authors.initials: L
authors.lastname: Chevillard
authors.affiliation: Assistance Publique - Hôpitaux de Paris, Lariboisière Hospital, Department of Medical and Toxicological Critical Care, Paris, France. Electronic address: isabellemalissin@gmail.com.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Malissin
authors.affiliation: Inserm, U1144, Paris, France; UMR-S 1144, Paris-Descartes University, Paris, France; UMR-S 1144, Paris-Diderot University, Paris, France. Electronic address: patricia.risede@inserm.fr.
authors.forename: Patricia
authors.initials: P
authors.lastname: Risède
authors.affiliation: Inserm, U1144, Paris, France; UMR-S 1144, Paris-Descartes University, Paris, France; UMR-S 1144, Paris-Diderot University, Paris, France; Assistance Publique - Hôpitaux de Paris, Lariboisière Hospital, Laboratory of Biochemistry and Molecular Biology, Paris, France. Electronic address: jacques.callebert@aphp.fr.
authors.forename: Jacques
authors.initials: J
authors.lastname: Callebert
authors.affiliation: Inserm, U1144, Paris, France; UMR-S 1144, Paris-Descartes University, Paris, France; UMR-S 1144, Paris-Diderot University, Paris, France; Assistance Publique - Hôpitaux de Paris, Cochin Hospital, Laboratory of Toxicology, Paris, France. Electronic address: laurence.labat@aphp.fr.
authors.forename: Laurence
authors.initials: L
authors.lastname: Labat
authors.affiliation: Assistance Publique - Hôpitaux de Paris, Lariboisière Hospital, Laboratory of Biochemistry and Molecular Biology, Paris, France; Inserm, U942, Paris, France. Electronic address: jean-marie.launay@aphp.fr.
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Launay
authors.affiliation: Inserm, U1144, Paris, France; UMR-S 1144, Paris-Descartes University, Paris, France; UMR-S 1144, Paris-Diderot University, Paris, France; Assistance Publique - Hôpitaux de Paris, Lariboisière Hospital, Laboratory of Biochemistry and Molecular Biology, Paris, France. Electronic address: jean-louis.laplanche@aphp.fr.
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Laplanche
authors.affiliation: Inserm, U1144, Paris, France; UMR-S 1144, Paris-Descartes University, Paris, France; UMR-S 1144, Paris-Diderot University, Paris, France; Assistance Publique - Hôpitaux de Paris, Lariboisière Hospital, Department of Medical and Toxicological Critical Care, Paris, France. Electronic address: bruno-megarbane@wanadoo.fr.
authors.forename: Bruno
authors.initials: B
authors.lastname: Mégarbane
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000633:toxicity*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D003975:Diazepam / Q000008:administration & dosage / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D062787:Drug Overdose; D008297:Male; D009420:Nervous System / Q000187:drug effects*; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism; D014147:Tramadol / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000633:toxicity*
chemical_list: D000701:Analgesics, Opioid; D012701:Serotonin; D014147:Tramadol; D003975:Diazepam; D009638:Norepinephrine
keywords: Diazepam; Poisoning; Respiratory depression; Seizure; Serotonin; Tramadol