title: A labetalol metabolite with analytical characteristics resembling amphetamines.
abstract: A metabolite of labetalol that is responsible for previous reports of false-positive assays for amphetamines by thin-layer chromatography and immunoassay has been identified. The compound, 3-amino-1-phenylbutane (APB), an oxidative metabolite of labetalol, was initially identified in a patient's urine by gas chromatography-mass spectrometry and confirmed by analysis of the pure material. Gas chromatography showed a single major peak with relative retention time indistinguishable from that of methamphetamine, both underivatized and as the pentafluoropropionyl derivative. By classical thin-layer chromatography, APB migrated identically to methamphetamine but showed ninhydrin color development characteristic of amphetamine. APB was shown to cross-react approximately 2% with the Abbott TDx amphetamine/methamphetamine II kit, 10% with the Syva EMIT d.a.u. polyclonal amphetamine class kit, and 3% with the Syva EMIT d.a.u. monoclonal amphetamine kit. This degree of cross-reactivity is sufficient to cause false-positive immunoassays when cutoffs of 300 ng/mL are used.
authors.affiliation: Department of Pathology, Santa Clara Valley Medical Center, San Jose, CA 95128, USA.
authors.forename: R B
authors.initials: RB
authors.lastname: Gilbert
authors.forename: P I
authors.initials: PI
authors.lastname: Peng
authors.forename: D
authors.initials: D
authors.lastname: Wong
mesh_terms: D000368:Aged; D000662:Amphetamines / Q000652:urine*; D002082:Butylamines / Q000652:urine*; D002849:Chromatography, Gas; D002855:Chromatography, Thin Layer; D005189:False Positive Reactions; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007741:Labetalol / Q000652:urine*
chemical_list: D000662:Amphetamines; D002082:Butylamines; C058063:3-amino-1-phenylbutane; D007741:Labetalol