Hair analysis for drugs of abuse. XVI. Disposition of fenethylline and its metabolite into hair and discrimination between fenethylline use and amphetamine use by hair analysis.

The incorporation tendency of fenethylline (FNT) and its metabolite into rat hair and the discrimination between FNT use and amphetamine (AP) use by hair analysis using gas chromatography-mass spectrometry with selected ion monitoring are described. After the intraperitoneal administrations of FNT to pigmented hairy rats (5 mg/kg/day, 10 days, n = 3), concentrations of FNT and its metabolite, AP, in the rat hair newly grown over 4 weeks were compared with area under the concentration versus time curves (AUCs) of the drugs in the rat plasma. The hair concentrations of FNT and AP were 52 +/- 1.4 and 4.9 +/- 0.6 ng/mg, whereas those of plasma AUCs were 55.9 +/- 23.1 and 22.3 +/- 4.9 micrograms.min/mL, respectively. The ratios of the hair concentrations to the AUCs of FNT tends to be highly incorporated into hair from suggests that FNT tends to be highly incorporated into hair from blood. The analytical method was applied to the determination of the metabolites in scalp hair of humans who were given FNT orally in multiple doses (50 mg/day, 3 days, n = 5) or in a single dose (50 mg/day, 1 day, n = 1). FNT and AP were detected at 0.51 +/- 0.23 and 0.35 +/- 0.12 ng/mg, respectively, in the proximal 1-cm hair segments from subjects given FNT orally for 3 days and 0.25 and 0.11 ng/mg, respectively, in the single-dose sample. In addition, it was found that the concentrations of FNT were 1.2 to 2.7 times greater than those of AP in the human hair samples, except for one sample, although FNT rapidly disappeared from the urine compared with AP. It was concluded that hair would be a good specimen for disclosure of drug history of FNT and for discrimination between FNT use and AP abuse.