Different localizations of drugs simultaneously administered in a strand of hair by micro‐segmental analysis

Segmental hair analysis is used to estimate the time of drug intake at monthly precision in drug‐related crimes. Previously, we advanced this analytical method to specify the day of drug intake by cutting a strand of hair into 0.4‐mm segments, which correspond to daily hair growth. Herein, we investigated the distributions of 7 compounds in a strand of hair using micro‐segmental analysis. Several strands of hair were collected 33.1?229.4 days after subjects were administered 4 pharmaceutical products that contained 10 drugs in single doses within 32 hours. The administered drugs and resulting metabolites were extracted from 0.4‐mm hair segments and quantified using liquid chromatography–tandem mass spectrometry. Acidic and neutral compounds were detected at low amounts in any of the hair segments analyzed. Epinastine, fexofenadine, dihydrocodeine, chlorpheniramine, and the chlorpheniramine metabolite, desmethylchlorpheniramine each was localized to 2 regions within a strand of hair. By contrast, methylephedrine and its metabolite, ephedrine, each was localized to only a region. Among 20 individual strands of hair associated with different subjects and head regions, few differences in the shapes of drug concentration–hair segment curves for each compound were detected. Our data indicated that 2 mechanisms for drug uptake into hair can operate depending on drug properties and that co‐administered drugs can be localized to different regions in a strand of hair. Micro‐segmental analysis may aid in the identification of the day of drug intake and help to elucidate the mechanisms of drug uptake into hair.