Testing for trazodone, an antidepressant, in hair collected from horses

Trazodone, a medicine registered for human, is a serotonin agonist-antagonist. At low dose, the drug is sedative due to its antagonist properties. At high dose, it is an agonist with anxiolytic and antidepressant actions. Trazodone can be administered to the horse to reduce anxiety. However, according to the antidoping rules for horses, the presence of trazodone in blood or urine is considered as a violation, which will produce a suspension of both the athlete and the horse as the drug is listed banned on the International Federation of Horseracing Authorities prohibited substances list. As a hair test can provide more evidence or supplementary information to an adverse analytical finding or to document drug exposure, our forensic laboratory received two specimens with a request for trazodone identification. After mane collection, trazodone was analysed by a new LC-MS/MS method involving pH 9.5 borate buffer overnight incubation of 20 mg of specimen in presence of clozapine-d4 used as internal standard, followed by solvents extraction. Linearity was verified from 1 to 100 pg/mg (R2 = 0.9967). Limit of detection of the method was 0.1 pg/mg. Trazodone was measured at 0.4 pg/mg in the mane of a horse suspended after an antidoping violation. In a case of hidden administration, trazodone was identified at 9 and 24 pg/mg in two consecutive mane hair segments. Although no controlled study allows interpretation, particularly about the frequency of exposure and the dose that entered in the body, this is the first evidence that trazodone can be incorporated in the mane of horses.