Studies on the metabolism and toxicological detection of the amphetamine-like anorectic fenproporex in human urine by gas chromatography–mass spectrometry and fluorescence polarization immunoassay

Studies on the metabolism and the toxicological analysis of fenproporex (R,S-3-[(1-phenyl-2-propyl)-amino]-propionitrile, FP) using GC–MS and fluorescence polarization immunoassay are described. The metabolites were identified in urine samples of volunteers by GC–MS after cleavage of conjugates, extraction and acetylation. Besides unchanged FP, fourteen metabolites, including amphetamine, could be identified. Two partially overlapping metabolic pathways could be postulated: ring degradation by one- and two-fold aromatic hydroxylation followed by methylation and side chain degradation by N-dealkylation to amphetamine (AM). A minor pathway leads via β-hydroxylation of AM to norephedrine. For GC–MS detection, the systematic toxicological analysis procedure including acid hydrolysis, extraction at pH 8–9 and acetylation was suitable (detection limits 50 ng/ml for FP and 100 ng/ml for AM). Excretion studies showed, that only AM but neither FP nor its specific metabolites were detectable 30–60 h after ingestion of 20 mg of FP. Therefore, misinterpretation can occur. The Abbott TDx FPIA amphetamine/methamphetamine II gave positive results up to 58 h. All the positive immunoassay results could be confirmed by the described GC–MS procedure.