New Method Detects Growth Hormone Secretagogue MK-0677 in Racehorses for Doping Control

Ibutamoren (MK-0677) is a potent growth hormone secretagogue (GHS), often misused in sports for its anabolic effects, leading to increased muscle mass and improved recovery. In Thoroughbred horse racing, the illicit use of performance-enhancing drugs poses a significant threat to fair competition and animal welfare. Current anti-doping efforts require robust analytical methods, but there was a lack of comprehensive characterization of MK-0677 and its metabolites in equine biological samples to establish effective detection windows.

The study successfully identified the parent compound, ibutamoren (MK-0677), and 3 major metabolites in both plasma and urine samples. The parent compound was detectable in plasma for up to 12 hours post-administration, while one key metabolite showed a significantly longer detection window. The most promising finding for doping control was the detection of a specific long-lived metabolite in urine for up to 72 hours post-administration, offering a 6-fold increase in detection time compared to the parent compound in plasma. This metabolite was present at concentrations allowing for reliable detection, even when the parent drug was no longer measurable, providing a robust biomarker for MK-0677 use. The developed LC-MS/MS method demonstrated high sensitivity, with a limit of detection (LOD) of 0.1 ng/mL for the key metabolite.