Time course detection of dihydrocodeine in body hair after a single dose

When head hair is not suitable or not available, body hair, such as leg or beard hair might be the most suitable sample for drug hair analysis. Information about the time course of drugs in hair, from the different anatomical body sites, should still be well documented.

The aim of this study was to determine and compare (a) the detection window of dihydrocodeine in frequently shaved legs and beard, (b) in unshaved hair from head hair, chest hair, leg hair, and/or arm hair, and (c) the distribution concentrations over the scalp, after a single dihydrocodeine intake.

Before a single intake of 12 mg dihydrocodeine by subject 1 (woman), both legs hair were shaved in the morning. The subject 2 (man) shaved his beard in the morning and 30 min later he had a dose of 10 mg of dihydrocodeine. The samples were washed with water and shampoo, dried and collected as follows: Subject 1: every 3-days shaved leg hair (n = 9) and 1-month-later head hair (n = 1). Subject 2: daily shaved beard hair (n = 15), 2 months later head hair (n = 145), and every 20 days unshaved arm, leg and chest hair (from different areas) (n = 4/area). The samples were analysed for dihydrocodeine using a validated liquid chromatography-tandem mass spectrometry method with a limit of quantification (LOQ) of 15.6 pg/mg for dihydrocodeine. About 20 mg of hair samples were weighted, washed with dichloromethane, centrifuged, dried, and pulverized in the same disposable tubes. Then the samples were incubated with methanol (under sonication at 45 °C) during 4 h. After centrifugation, the supernatant was evaporated and a cation exchange solid phase extraction followed by separation and quantification using ultra performance liquid chromatography-tandem mass spectrometry (ULC-MS/MS) was carried out. Chromatographic separation was achieved using a BEH phenyl column eluted with 0.1% formic acid: methanol (0.1% formic acid). The UPLC-MS/MS method was validated and used in routine for drug hair analysis for already several years.

In the present study leg hair was collected every 3 days, as an average of frequent shaved hair in western woman population. Shaved leg hair was very limited and only one hair sample was available per analysis. Beard was collected daily and in a higher amount. Dihydrocodeine was detected in leg hair from the first sample (3 days after the intake). Maximum concentration at 68 pg/mg for the single intake was obtained after 15 days (±2 days), decreasing later to the LOQ from the 21th day. Beard hair was positive from the first day sample, and the maximum concentration was observed at 66 pg/mg, 6 days after the intake, decreasing later to the LOQ from day 13. This may be explained by growth rate and the amount of growing hairs, in anagen phase. In other body hair samples, dihydrocodeine was negative or detected from 1 month after the intake. No significant differences in dihydrocodeine concentrations over the scalp in the different regions were observed (p > 0.05).

Body hair presents different time course window detection due to the different growth rates. Frequently shaved leg and beard hair may be suitable samples for recent single dihydrocodeine dose detection from the first days up to 2-3 weeks after the intake, respectively, when a LOQ of 15.6 pg/mg is applied.