Detection of the growth hormone secretagogue MK-0677 in equine hair following oral administration.

This study investigated whether MK-0677 (ibutamoren), an orally active, non-peptide growth hormone secretagogue that activates the ghrelin receptor, could be detected in equine hair following oral administration to a single Thoroughbred racehorse. Researchers extracted MK-0677 and its O-dealkylated metabolite from mane and tail hair samples using an established method for prohibited substances, then analyzed them by liquid chromatography tandem mass spectrometry (LC-MS/MS). The study found that MK-0677 was detectable in all collected hair samples, with a detection window of up to 209 days in mane hair and 358 days in tail hair. A follow-up wash procedure confirmed true internal incorporation of the compound rather than mere surface contamination. Wash criteria analyses suggested that hair samples collected at later time points (≥52 days post-administration) reflected internal incorporation via the bloodstream, while the earliest sample (2 days) showed a combination of internal incorporation and external deposition via sweat and sebum. A key limitation is that the study involved only one horse, restricting generalizability. The findings are relevant to anti-doping efforts in equine sports, highlighting the long detection window MK-0677 may afford in hair matrices.

Why this grade: The study was conducted exclusively in a single Thoroughbred racehorse with no human subjects, providing pharmacokinetic and detection data relevant only to the equine context.