Hair analysis for drugs of abuse. XI. Disposition of benzphetamine and its metabolites into hair and comparison of benzphetamine use and methamphetamine use by hair analysis.

In order to study the disposition of benzphetamine (BZP) and its metabolites, desmethyl benzphetamine (norBZP), p-hydroxy desmethyl benzphetamine (OHnorBZP), methamphetamine (MA) and amphetamine (AP), from plasma to hair in rats, an analytical method for identifying these drugs in plasma, urine and hair was developed with selected ion monitoring of gas chromatograph/mass spectrometry (GC/MS-SIM) results. After the intraperitoneal administration of BZP to rats (10 mg/kg/d, 10d, n = 3), concentrations of BZP and its metabolites in rat hair newly grown for 4 weeks were compared to the areas under the concentration versus time curve (AUCs) of these drugs in the rat plasma. The concentrations of BZP, norBZP, OHnorBZP, MA and AP in the rat hair were 14.8 +/- 1.4, 6.1 +/- 0.3, 2.6 +/- 0.5, 2.3 +/- 0.1 and 9.2 +/- 0.3 ng/mg, and the ratio of the concentrations in the hair to AUCs in the rat plasma was 3.0:0.1:0.1:0.6:0.2, respectively. This fact suggested that BZP tends to be readily incorporated into hair from blood. The method was applied to the determination of the metabolites in scalp hair and pubic hair of humans who orally ingested BZP (30 mg/d, 5d, n = 2). BZP, norBZP, MA and AP were detected at 0.14-0.56, 0.29-0.63, 0.10 and 1.06-1.66 ng/mg in the scalp hair and at 0.10-0.20, 0.13-0.18, trace-0.15 and 0.23 ng/mg in the pubic hair, respectively. It was shown that BZP use could be retrospectively distinguished from MA use by the detection of BZP and/or norBZP in hair.