Hair analysis to discriminate voluntary doping vs inadvertent ingestion of the aromatase inhibitor letrozole.

Letrozole is an aromatase inhibitor, used to treat postmenopausal women with hormone receptor-positive or unknown advanced breast cancer. It is prohibited in sport because it is used together with androgen anabolizing steroids to avoid their adverse effects. In the case of an adverse analytical finding, it may be important to distinguish between repetitive use due to voluntary administration and occasional use, possibly due to involuntary intake. With the objective to identify the dose capable of producing a positive hair test, and to apply these results to the scenarios of inadvertent letrozole ingestion by an athlete, this study investigates the urinary excretion and incorporation into hair of single doses of letrozole. Seven subjects were recruited for an excretion study of letrozole and its metabolite bis(4-cyanophenyl) methanol (M1) in urine, after the consumption of 0.62 mg, 1.25 mg, and 2.5 mg of letrozole, and to investigate the incorporation in hair after ingestion of 0.62 mg and 2.5 mg of letrozole. Urine and hair samples were also obtained from two women in chronic therapy. Urinary concentrations of letrozole and its metabolite M1 were lower in subjects administered once with 0.62 mg, 1.25 mg, or 2.5 mg letrozole than in women in regular therapy with 2.5 mg/day. In hair collected after a single dosage, concentrations of 16-60 pg/mg were detected while in women in chronic therapy concentrations were higher than 160 pg/mg all along the hair shaft. Hair analysis turned to be a promising possibility for the discrimination of letrozole repetitive use vs occasional/inadvertent administration.