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

Abstract

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.

Sports drug testing and the athletes' exposome

“…The complexity and extent of today's drug contaminants and resulting routes of exposure was excellently summarized in 2011 by Daughton, 91 and numerous of the above discussed aspects were discussed in the context of forensic epidemiology and toxicology, including interpersonal dermal transfer of drugs 92 . In addition to these potential contributors to the athlete's exposome, also other factors could require consideration such as shared household equipment or jointly prepared food, 93 and the substantial intricacy appears to have further increased in the past decade as the exposure to drugs and chemicals by elite athletes that are subjected to routine doping controls adds another level of relevance concerning the potential consequences.…”

Annual banned‐substance review – Analytical approaches in human sports drug testing

“…While this proposal is plausible considering the enforced Prohibited List, an ongoing debate exists concerning the general relevance of banning aromatase inhibitors in females, which was further fomented by an AAF concerning letrozole. Differentiating the misuse of the drug from a single inadvertent and accidental intake by means of a single doping control urine sample is particularly difficult, and hence the applicability of hair testing was assessed by Favretto et al who investigated the traceability and concentration range of letrozole in hair following single dose and chronic letrozole use . In a pilot study setting, amounts of 0.62 mg, 1.25 mg, and 2.5 mg were orally administered, and urine samples were collected over a period of 9 days.…”

Hair testing for doping agents. What is known and what remains to do

“…When dealing with an unusual drug (for example, a drug which has gain no interest in clinical or forensic toxicology), one should encourage the laboratory performing the hair test to address the following questions: is a single pharmacological dose detectable in hair? what is the minimal detectable dose? what are the expected hair concentrations of patients using the same drug for therapeutic purposes? what (if any) is the influence of hair colour? what (if any) is the influence of hair cosmetic treatment? In 2019, these points have been published for letrozole, a S4 aromatase inhibitor and for hydrochlorothiazide, a S5 diuretic, allowing to document the negative hair findings and it was concluded by the authors that hair analysis turned to be a possibility for the discrimination of drug repetitive use vs inadvertent exposure.…”

“…12 It contains the list of substances prohibited at all times and those prohibited in-competition. With respect to the list, Table 1 presents a compendium of selected literature papers [13][14][15][16][17][18][19][20][21][22][23][24] dealing with doping agent detection in human hair. Although several compounds from the same class have been identified in hair, the aim of this table was just to indicate whether within each specific class one substance has already been identified.…”