Urinary output changes in racemic ethylamphetamine and optical activity discrimination in rat urine by HPLC analysis

Characterization of optical activity and simultaneous analysis of racemic ethylamphetamine (EAMP) and its metabolites, as well as the urinary excretion of the optical isomers, were examined in rats by high-performance liquid chromatography (HPLC). Analysis of the optical isomers of EAMP, amphetamine (AMP), para-hydroxy-ethylamphetamine (p-OH-EAMP), and para-hydroxy-amphetamine (p-OH-AMP) was performed within 90 min. The limit of detection was 30 ng for EAMP and AMP, and 60 ng for p-OH-EAMP and p-OH-AMP per 20 microliters injection. After oral administration of racemic EAMP, rat urine specimens were collected at four intervals, 0-4, 4-12, 12-20 and 20-24 h. After administration of 30 mg/kg EAMP, not only each isomer of EAMP, i.e. AMP, p-OH-EAMP and p-OH-AMP, but also an unidentified substance (UI) were detected. The UI was presumed to be 3-hydroxy-4-methoxy-N-EAMP or 3-methoxy-4-hydroxy-N-EAMP by gas chromatographic mass spectrometry (GC-MS) analysis. The d-isomer of EAMP was generally excreted more abundantly than the l-isomer (p < 0.01-0.05). The d-isomer of AMP and p-OH-EAMP was excreted in the first 4 h in a somewhat smaller amount than the l-isomer but thereafter in a greater amount than the l-isomer. The d-isomer of p-OH-AMP was generally excreted in a smaller amount than the l-isomer (p < 0.1-0.05). The total percentages of the dose excreted up to 24 h were 2.65% of the dose of EAMP administered [d: 2.04% and l: 0.61%], AMP 3.15% [d: 1.68% and l: 1.47%], p-OH-EAMP 63.06% [d: 32.68% and l: 30.38%], and p-OH-AMP 2.57% [d: 1.05% and l: 1.52%]. The optical purity ratio (l/d) of EAMP up to 24 h was 0.31, significantly lower than that (1.03) of the original racemic EAMP (p < 0.01). The changes in the excretion of EAMP and AMP indicated a stereoselective disposition, but those of p-OH-EAMP and p-OH-AMP were unremarkable: the d- and the l-isomer of p-OH-EAMP and p-OH-AMP did not differ significantly. The entire amount excreted up to 24 h was about 71.43% of the dose administered; the d-isomer 37.45% and the l-isomer 33.98%. The l/d was 0.91, which was clearly less than that of the original racemic EAMP (p < 0.01). These results suggested stereoselective disposition of EAMP in the rat, and the methods are potentially applicable to identification of the optical activity of EAMP and thereby of methamphetamine abusers.