IDENTIFICATION OF FENTANYL METABOLITES IN RAT URINE BY GAS CHROMATOGRAPHY-MASS SPECTROMETRY WITH STABLE-ISOTOPE TRACERS

Abstract

The metabolites of fentanyl (I), a neuroleptic analgesic agent, were identified in urine of rats by gas chromatography-mass spectrometry [AC/MS] combined with a stable-isotope tracer technique. After the oral administration of an equimolar mixture of I and deuterium-labeled I (I/I-d5), the urinary metabolites were extracted with chloroform at pH 9.0. Extracts were derivatized and analyzed by GC/MS. Metabolites were identified by the presence of doublet ion peaks separated by 5 amu [atomic mass units], and chemical structures were established from analyses of fragmentation pathways. The metabolites were identified as 4-N-(N-propionylanilino)-piperidine, 4-N-(N-hydroxypropionylanilino)piperidine, 4-N-(N-propionylanilino)hydroxypiperidine, 1-(2-phenethyl)-4-N-(N-hydroxypropionylanilino)piperidine and 1-(2-phenethyl)-4-N-(N-propionylanilino)hydroxypiperidine. These metabolites, together with unchanged I, were also detected in urine of rats receiving I/I-d5 i.v., by selected-ion monitoring of the specific cluster ions.