Investigations Into the Metabolism and Elimination of Tesofensine in Human Urine

Tesofensine (NS-2330) is a pharmacologically active compound with weight-reducing effects in obese patients. Although still under regulatory review, it has been marketed online as a dietary supplement promoted for weight management and metabolic enhancement. Due to its impact on body weight, tesofensine could be relevant in competitive sports, particularly in weight-class disciplines and sports where power-to-weight ratio is decisive. It is classified under "S6 stimulants" on the World Anti-Doping Agency's Prohibited List and is prohibited in-competition only, making detailed knowledge of its metabolism and excretion essential for anti-doping purposes. Although the pharmacological effects and elimination of tesofensine and one dealkylated metabolite were described previously, elimination profiles and structural information on additional metabolites have been limited. In this study, in vitro metabolism experiments were conducted, followed by investigation of urinary metabolism and elimination in six volunteers after ingestion of 483 μg tesofensine as a dietary supplement. Urine was collected for up to 600 h, prepared by solid-phase extraction, and analyzed by LC-HRMS. Four principal metabolites were identified: three dealkylated metabolites (M1-M3) and one hydroxylated and glucuronidated metabolite (M4), supported by MS/MS dissociation patterns. The validated analytical method for human urine showed an LOD of 0.01 ng/mL, 34% recovery, and 8% interday imprecision. Marked interindividual variability was observed, with peak concentrations of 1-4 ng/mL after 4-46 h and detection windows up to 500 h. The findings enhance analytical procedures and suggest that recommended dosing is unlikely to result in concentrations constituting an Adverse Analytical Finding (AAF) under currently applicable stimulant minimum reporting levels.