The influence of the route of drug administration on the metabolic profile of trenbolone in doping control urine samples

Advances in analytical techniques have markedly improved the detection of anabolic-androgenic steroids (AAS) in doping controls. This represents a major success for anti-doping efforts, but at the same times raises concerns about inadvertent exposure - not limited to oral ingestion, but also via dermal contact or mucosal absorption. Evaluating the plausibility of such scenarios can be complex, not least because these routes of drug intake can also be deliberately used for doping purposes. Analytical data on transdermal or mucosal absorption and elimination of AAS can be valuable here, particularly regarding the metabolite pattern in urine samples that might help to assess the route of drug delivery. This study investigated the urinary excretion profile of trenbolone and its metabolites after oral, transdermal and buccal administration in healthy male volunteers. Urine samples collected over a period of one week following the administration of 10 mg of trenbolone were analyzed by LC-HRMS, with regard to potential differences in the metabolite profile across the different routes of drug intake. Major trenbolone metabolites were detectable in the urine samples of all participants, however the detection windows varied strongly: Buccal resorption resulted in faster elimination, whereas transdermal application resulted in prolonged detectability, compared to oral administration. A cysteine-conjugated metabolite (M15-cys) was identified that showed higher abundances following transdermal and buccal administration, suggesting its potential as a marker for non-oral intake. In light of the growing importance of transdermal uptake of doping agents, these results provide valuable data for interpreting doping control findings, potentially also relevant for structurally related AAS.