Clobenzorex (Asenlix) is an
anorectic drug metabolized by the body to
amphetamine, thus causing difficulty in the interpretation of
amphetamine-positive
drug tests. Previous studies have shown the parent
drug and several metabolites are excreted in urine.
Clobenzorex itself has been detected for as long as 29 h postdose using a detection limit of 1 ng/mL. Despite this fact, several
amphetamine-positive samples (> or = 500 ng/mL) contained no detectable
clobenzorex. Thus, the absence of
clobenzorex in the urine does not exclude the possibility of its use. To more definitively assess the possibility of
clobenzorex use, evaluation of another metabolite was considered. One study reported the presence of unidentified hydroxy metabolites of
clobenzorex for as long as
amphetamine was detected in some subjects. To assess the viability of using a hydroxy metabolite to confirm the use of
clobenzorex in samples containing
amphetamine,
4-hydroxyclobenzorex was synthesized for this study. This metabolite proved to be easily detected and was typically found at levels higher than
amphetamine in
amphetamine-positive urines, long after
clobenzorex itself was no longer detected. Samples obtained from a controlled single-dose study involving the administration of
clobenzorex (30 mg) were analyzed for the presence of the 4-hydroxy metabolite. The analytical procedure used
acid hydrolysis followed by liquid-liquid extraction and analysis with gas chromatography-mass spectrometry by monitoring
ions at m/z 125, 330, and 364.
4-Hydroxyclobenzorex and its 3-Cl regioisomer were used in the identification and quantitation of the metabolite. Peak concentrations of
4-hydroxyclobenzorex were found at approximately 1:30-5:00 h postdose and ranged from approximately 5705 to 88,410 ng/mL. Most importantly, however, all samples that contained
amphetamine at > or = 500 ng/mL also contained detectable amounts of this hydroxy metabolite (LOD 10 ng/mL), making it a valuable tool in differentiating use of
clobenzorex from illicit
amphetamine use.