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