Exploring transdermal SARMs exposure: analysis of the elimination profiles and metabolism for doping control purposes

Transdermal drug delivery has been of particular interest to pharmaceutical research for decades, but is also becoming increasingly relevant in the field of sports drug testing. As shown in the past, the (unintentional) oral ingestion of trace amounts of prohibited selective androgen receptor modulators (SARMs), e.g. due to product contamination, can lead to an adverse analytical finding (AAF) in doping controls. Another site of exposure is presented by the skin, as it provides a large surface for drug penetration. However, the extent of diffusion through various layers of the skin and into the blood vessels depends, among other things, on the physicochemical and biological properties of a substance. The objective of this project was to simulate a transdermal contamination scenario and investigate the skin penetration and subsequent metabolism of microdoses of three commonly used SARMs: LGD-4033, RAD140, and S-23. For this purpose, an administration study was conducted, in which either 10 or 50 µg of the substances were applied to the lower forearm of 5 volunteers each. The collected urine samples were analyzed via LC-MS/MS following enzymatic hydrolysis and solid-phase extraction. This methodical approach is distinguished by its high sensitivity, enabling the detection of at least 5 pg/mL for LGD-4033 and S-23. After 10 µg administration, LGD-4033 and S-23 as well as associated metabolites were detected, while RAD140 was only detected in urine samples of one subject (n = 5). Following the application of 50 µg, RAD140 was detected in all subjects (n = 5) for up to 9 days, and additional metabolites of LGD-4033 and S-23 were identified. The long-term metabolite of LGD-4033 (M5b) was detected up to 12 days after the dermal administration of 10 µg, and up to 25 days after application of 50 µg, while S-23 was traceable for up to 16, respectively 24 days. It was demonstrated for all three SARMs that they penetrate the skin and may-even in trace amounts-produce AAFs when administered transdermally. Information on urinary concentrations and metabolism following transdermal administration of SARMs may assist in the interpretation of AAFs, particularly when dermal contamination or intentional doping via the skin is discussed.