Detection of FG‐4592 and metabolites in equine plasma, urine and hair following oral administration

FG‐4592 is a hypoxia‐inducible factor inhibitor that has been approved for therapeutic use in some countries. This class of compounds can increase the oxygen carrying capacity of the blood and thus have the potential to be used as performance enhancing agents in sports. The purpose of this study was to investigate the detection of FG‐4592 and metabolites in equine plasma and mane hair following a multiple dose oral administration to two Thoroughbred racehorses, to identify the best analytical targets for doping control laboratories. Urine samples were also analysed, and the results compared to previously published urine data. Liquid chromatography‐high resolution mass spectrometry was used for metabolite identification in urine and plasma. Liquid chromatography–tandem mass spectrometry was used for full sample analysis of urine, plasma and hair samples and generation of urine and plasma profiles. FG‐4592 and a mono‐hydroxylated metabolite were detected in plasma. FG‐4592 was detected with the greatest abundance and gave the longest duration of detection, up to 312 h post‐administration, and would be the recommended target in routine doping samples. FG‐4592 was detected in all mane hair samples collected post‐administration, up to 166 days following the final dose, showing extended detection can be achieved with this matrix. To the best of the authors' knowledge, this is the first report of FG‐4592 and metabolites in equine plasma and hair samples. Urine results were consistent with the previously published data, with FG‐4592 offering the best target for detection and longest detection periods. Hypoxia‐inducible factor inhibitors, including FG‐4592, are prohibited in sports, and thus identifying the best targets for their detection in doping control is essential. Analysis of equine urine, plasma and hair showed that the parent drug was the best target for detection of oral administration in all three matrices.