Urinary excretion and metabolism of orally administered mefenorex

Metabolic pathways and the pharmacokinetic profile of mefenorex ((+/-)N-(3-chloropropyl)-1-methyl-2-phenylethylamine), and its main metabolite amphetamine (1-methyl-2-phenylethylamine) have been studied in two healthy volunteers, after a single oral dose of mefenorex (1.2 mg/kg body weight for a male subject and 2.4 mg/kg body weight for a female subject). Urinary concentrations were determined by gas chromatography (GC) and metabolite structure was identified by GC/MS following derivatization of urine extracts. The ratio of this metabolite to unchanged drug in urine samples, collected up to 5 h following administration, was essentially the same after either of the administered doses. The calculated Kel for mefenorex after the higher dose was in the range of 0.191-0.272 h-1, with a biological half life (t1/2) of 3.98-2.55 h, depending on the method of calculation used. The elimination of amphetamine was much slower with a Kel ranging from 0.039-0.073 h-1 and a t1/2 from 9.5-17.8 h. Depending on the dose administered, the rate constant of metabolite formation was 0.129 and 0.685 h-1 for low and high doses, respectively. Urinary excretion of Rondimen amounted to 11.9% within 72 h after administration. Of this amount, 1.5% represented unchanged drug and 10.4% represented metabolites. In addition to amphetamine 3 other metabolites were identified: p-hydroxy mefenorex, p-hydroxy amphetamine and p-hydroxy-m-methoxy mefenorex.