DEMONSTRATION OF CLOBENZOREX EXPOSURE AS AN EXPLANATION FOR GC/MS-CONFIRMED POSITIVE URINE TESTS SPECIFIC FOR AMPHETAMINE

Background: Exposure to prescription diet drugs other than amphetamine and methamphetamine may cause GC/MS-confirmed, and therefore chemically specific, positive urine drug tests for amphetamine. This is explained by the metabolism of these drugs, e.g., clobenzorex, to amphetamine, which is then excreted in amounts that exceed federal drug test cut-off levels. Drug reference information and laboratory standards needed to verify exposure to such drugs are largely unavailable. A case is presented that demonstrates the value of analytical laboratory investigation beyond the initial GC/MS confirmation of the urinary presence of amphetamine. Case Report: Investigation of a GC/MS-confirmed laboratory positive workplace urine test for amphetamine suggested use of an unidentified Mexican diet drug by the specimen donor. Pharmaceutical reference source consultation tailed to reveal the identity of donor-provided drug samples. Discussion with a US representative of the suspected pharmaceutical manufacturer and GC/MS analysis of the drug samples strongly suggested, but did not confirm, that the samples contained clobenzorex. Self-administration of drug sample by one of the authors, followed by chemical derivatization, solid phase extraction, and GC/MS analysis of urine collected at 4 hours postexposure revealed acetylated derivatives of clobenzorex (S-(+)-N-(2-chlorobenzyl)-amphetamine) and associated metabolites, including amphetamine, 4-OH-amphetamine, and norephedrine. Conclusion: Demonstration of the urinary presence of clobenzorex metabolites other than amphetamine by GC/MS analysis corroborates exposure to clobenzorex as an explanation for a GC/MS-confirmed positive urine drug test for amphetamine.
Wallace KL, Gerkin R, Gatewood P. Good Samaritan Regional Medical Center, Phoenix, [...]