Toxicological detection of selegiline and its metabolites in urine using fluorescence polarization immunoassay (FPIA) and gas chromatography-mass spectrometry (GC-MS) and differentiation by enantioselective GC-MS of the intake of selegiline from abuse of methamphetamine or amphetamine

Abstract

Selegiline (R(-)-N-methyl-N-(1-phenyl-2-propyl)-2-propinylamine), a selective MAO-B inhibitor used as an antiparkinsonian, is excreted in urine as N-desmethyl selegiline (norselegiline),R(-)-methamphetamine (R(-)-MA),R(-)-amphetamine (R(-)-AM) and their conjugated p-hydroxy derivatives. We found that the fluorescence polarization immunoassays (FPIA) TDx amphetamine/methamphetamine II (AM/MA II) and TDx amphetamine class (AM class) lead to positive results for up to 2 days after a single oral dose of 10 mg selegiline (detection limit: 0.1 mg/l, each). Every urine specimen from long term selegiline patients (10 mg/day) showed positive TDx results during the selegiline regimen. Positive TDx results were confirmed using gas chromatography-mass spectrometry (GC-MS). Selegiline metabolites, particularly MA, could be detected in urine for up to 7 days after intake of a single oral dose of 10 mg selegiline (detection limit: 0.01 mg/l for MA and AM). Norselegiline, the only specific selegiline metabolite, was only detectable for about 12 h. Moreover, norselegiline was not detected in all urine samples from long term selegiline patients (10 mg/day). Since differentiation of selegiline intake from MA/AM abuse by detecting norselegiline was not possible in most cases, an enantioselective GC-MS procedure was developed. It allowed differentiation of the enantiomers of the selegiline metabolites and thereby separation of selegiline intake (onlyR(-)-enantiomers) from methamphetamine and/or amphetamine abuse (racemates orS(+)-enantiomers). After derivatization withS(-)-N-trifluoroacetyl-prolyl chloride (TPC), the two enantiomers of MA and AM were each separated as diastereomers employing the routinely used achiral GC capillary. To prove the enantiomeric identity of MA and AM, before extraction, theirR(-)-enantiomers were added to the urine samples which were tested positive in the TDx. Presence ofS(-)-enantiomers of MA or AM revealed MA or AM abuse, whereas with selegiline intake only theR(-)-enantiomers of MA and/or AM were found. This enantioselective GC-MS procedure was sensitive enough to confirm all positive TDx results (detection limit: 0.1 mg/l for MA and AM).