Quantification of the Carboxylated LGD‐4033 Long‐Term Metabolite in Human Micro‐Dose Excretion Study Urine Samples

Abstract

ABSTRACT Selective androgen receptor modulators (SARMs), such as LGD‐4033, are frequently detected in doping control samples and pose significant challenges for result interpretation, particularly at low concentration levels potentially arising from contamination. In this study, a quantitative method for the determination of the carboxylated long‐term metabolite (M5‐b) of LGD‐4033 in human urine was developed and applied to samples obtained from controlled micro‐dose administration studies. Urine samples from single‐ and multiple‐dose administration studies (1, 10, and 50 μg) were analyzed following enzymatic hydrolysis and solid‐phase extraction using LC‐HRMS/MS. Quantification was enabled by the use of a recently synthesized certified reference material, allowing, for the first time, the generation of quantitative excretion data for long‐term metabolite under micro‐dose conditions. The results demonstrated the rapid formation of long‐term metabolite and a clear dose‐dependent increase in urinary concentrations. Extended detection windows were observed for all dosing regimens, with long‐term metabolite remaining detectable for several days after single‐dose administration and for substantially longer periods following consecutive administration (5 days). Accumulation effects during multiple‐dose intake resulted in sustained urinary concentrations and prolonged detectability. The quantitative data generated in this study provide an important basis for improved interpretation of adverse analytical findings involving LGD‐4033 and support a more evidence‐based distinction between different intake scenarios.