Elimination profiles of microdosed ostarine mimicking contaminated products ingestion

The possibility of nutritional supplement contamination with minute amounts of the selective androgen receptor modulator (SARM) ostarine has become a major concern for athletes and result managing authorities. In case of an adverse analytical finding (AAF), affected athletes need to provide conclusive information, demonstrating that the test result originates from a contamination scenario rather than doping. The aim of this research project was to study the elimination profiles of microdosed ostarine and characterize the time-dependent urinary excretion of the drug and selected metabolites. Single- and multi-dose administration studies with 1, 10, and 50 μg of ostarine were conducted, and collected urine samples were analyzed by LC-MS/MS following solid-phase extraction or enzymatic hydrolysis combined with liquid-liquid extraction. In the post-administration samples, both the maximum urine concentrations/abundance ratios and detection times of ostarine and its phase-I and phase-II metabolites were found to correlate with the administered drug dose. With regard to the observed maximum levels of ostarine, the time points of peak urinary concentrations/abundance ratios, and detection windows, a high inter-individual variation was observed. However, the study demonstrated that a single oral dose of as little as 1 μg can be detected for up to 9 (5) days by monitoring ostarine (glucuronide), and hydroxylated metabolites (especially M1a) appear to offer a considerably shorter detection window. The obtained data on ostarine (metabolite) detection times and urinary concentrations following different administration schemes support the interpretation of AAFs, in particular when scenarios of proven supplement contamination are discussed and supplement administration protocols exist.