Can a single dose of cetirizine and meclizine be quantified in hair up to one year after intake?

Cetirizine and meclizine are over-the-counter H1 antihistamines available in many countries. Meclizine can have a considerable sedative effect and can therefore be used in drug-facilitated crimes to incapacitate victims. Cetirizine does not usually produce a sedative effect but is often detected in drug-facilitated crimes. Quantification possibilities, reference concentrations, and temporal patterns of these antihistamines in hair, however, remain unknown. A single-dose study was conducted to investigate whether a single dose of cetirizine and meclizine could be quantified in head hair up to one year after intake. Twelve adult volunteers ingested a single dose of cetirizine (8.4 mg) and meclizine (23 mg). Hair samples were collected one, three, five, and twelve months after intake and analyzed using LC-MS/MS, with a lower limit of quantification of 1 pg/mg. Cetirizine was quantifiable in 100%, 100%, and 92% of the hair samples collected one, three, and five months post-intake, respectively. Meclizine was quantifiable in 100%, 92%, and 67% of the corresponding samples. In contrast, at one year post-intake, cetirizine and meclizine were quantifiable in only 40% and 10% of hair samples, respectively. Concentrations determined in 1-cm-long hair segments within one year after intake ranged from 0 to 14 pg/mg for cetirizine and from 0 to 19 pg/mg for meclizine. The findings demonstrate that a single dose of cetirizine or meclizine may be detectable and quantifiable in hair for several months. Moreover, temporal patterns following a single dose may resemble those observed after repeated intake, highlighting the need for drug-specific single-dose studies.