title: In vitro metabolism of tiletamine, zolazepam and nonbenzodiazepine sedatives: Identification of target metabolites for equine doping control.
abstract: Within horseracing, the detection of prohibited substance doping often requires urine analysis; hence, it is necessary to understand the metabolism of the drugs in question. Here, the previously unknown equine metabolism of eight sedatives is reported in order to provide information on target metabolites for use in doping control. Phase I metabolite information was provided by incubation with equine liver S9 fraction. In vitro techniques were chosen in order to reduce the ethical and financial issues surrounding the study of so many compounds, none of which are licensed for use in horses in the UK. Several metabolites of each drug were identified using liquid chromatography-high resolution mass spectrometric (LC-HRMS) analysis on an LTQ-Orbitrap. Further structural information was obtained by tandem mass spectrometry (MS/MS) analysis; allowing postulation of the structure of some of the most abundant in vitro metabolites. The most abundant metabolites of alpidem, etifoxine, indiplon, tiletamine, zaleplon, zolazepam, zolpidem, and zopiclone related to hydroxylation/N-oxidation, deethylation, demethylation, deethylation, hydroxylation/N-oxidation, demethylation, hydroxylation/N-oxidation and hydroxylation/N-oxidation, respectively. In many cases, further work would be required to fully elucidate the precise positioning of the functional groups involved. The results of this study provide metabolite information that can be used to enhance equine anti-doping screening methods. However, the in vitro metabolites identified are at present only a prediction of those that may occur in vivo. In the future, any positive findings of these drugs and/or their metabolites in horse urine samples could help validate these findings and/or refine the choice of target metabolites.
authors.affiliation: HFL Sport Science Ltd, Newmarket Road, Fordham, Cambridgeshire, CB7 5WW, UK. sfenwick@hfl.co.uk
authors.forename: Susanna J
authors.initials: SJ
authors.lastname: Fenwick
authors.forename: James P
authors.initials: JP
authors.lastname: Scarth
mesh_terms: D000818:Animals; D002492:Central Nervous System Depressants / Q000378:metabolism*; D002853:Chromatography, Liquid / Q000379:methods; D004300:Doping in Sports; D006736:Horses / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D015813:Substance Abuse Detection / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000379:methods; D013992:Tiletamine / Q000378:metabolism*; D015041:Zolazepam / Q000378:metabolism*
chemical_list: D002492:Central Nervous System Depressants; D013992:Tiletamine; D015041:Zolazepam