Study summary · research use only
Equine metabolism of the growth hormone secretagogue MK-0677 in vitro and in urine and plasma following oral administration
Plain-language summary
Paraphrased from the published abstract below — not a verdict on whether anything works.
In this equine study (in vitro incubation and oral administration to two Thoroughbred racehorses), the authors examined metabolism of the growth hormone secretagogue MK-0677 (ibutamoren mesylate). Using liquid chromatography high resolution mass spectrometry for metabolite identification and liquid chromatography-tandem mass spectrometry for metabolite profiling, they report that Fourteen phase I metabolites were identified in vitro; 13 of these were subsequently detected in urine and nine in plasma after administration, alongside the parent compound in both matrices. The longest duration of detection in both urine and plasma was for an O-dealkylated metabolite of MK-0677, which the authors identify as the most appropriate target for detecting MK-0677 use. MK-0677 and this metabolite were reported to be excreted largely unconjugated in urine and plasma.
Abstract
Ibutamoren mesylate, or MK-0677, is an orally active, nonpeptide growth hormone secretagogue that has been developed to stimulate excretion of endogenous growth hormone. It has been evaluated for the treatment of a range of clinical conditions but is not available therapeutically. Nonetheless, MK-0677 is widely available to purchase online, sold as 'supplement' products. The mode of action and relative ease of purchase make MK-0677 a potential threat with regard to sports doping. The aim of this study was to investigate the metabolism of MK0677 in the horse following in vitro incubation and oral administration to two Thoroughbred racehorses, in order to identify the most appropriate analytical targets for doping control laboratories. Liquid chromatography high resolution mass spectrometry was used for metabolite identification, and subsequently, liquid chromatography-tandem mass spectrometry was used to generate full metabolite profiles for post-administration urine and plasma samples. Fourteen phase I metabolites were identified in vitro; 13 of these were subsequently detected in urine and nine in plasma collected post-administration, alongside the parent compound in both matrices. In both urine and plasma, the longest duration of detection was observed for an O-dealkylated metabolite of MK-0677, and therefore, this would be the best target for the detection of MK-0677 administration. MK-0677 and the O-dealkylated metabolite were found to be excreted largely unconjugated in urine and plasma.
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