Abstract

In rats treated ip with N-ethylbenzamide (EB) at doses of 250-500 mg/kg, this amide was metabolized by hydrolysis to ethylamine and benzoic acid, the latter detected in the urine as hippuric acid. Proposed metabolic pathways were investigated by treatment of male Wistar rats with EB and N-ethyl-alpha-13C-benzamide followed by examination of urine samples by high-resolution NMR spectroscopy. Ethylamine was detected by 1H and 13C NMR techniques. Estimation of metabolite levels in 24-hr posttreatment urine by 1H NMR spectroscopy with an internal standard of 3-(trimethylsilyl)-1-propanesulfonic acid and correction for background levels of hippuric acid in control urine showed that the percentage of the dose excreted as hippuric acid was 52-76%. The corresponding range for the excretion of ethylamine (detected as an ethylammonium cation) was 27-41%. Signals for EB, benzamide, and benzoic acid were not above the background in urine of treated animals. A similar NMR study with unlabeled p-chloro-N-ethylbenzamide (p-Cl EB) resulted in the detection of p-chlorohippuric acid and ethylamine. Treatment of rats with N,N-diethylbenzamide and p-chloro-N,N-diethylbenzamide gave the same detectable metabolites in the urine as those found in experiments with EB and p-Cl EB. These observations could be rationalized with a metabolic pathway involving an initial oxidative mono-N-deethylation reaction followed by enzymatic hydrolysis of the secondary amides to ethylamine and benzoic acids and conjugation of the latter with glycine. N-Methylbenzamide was also found to be eliminated in the urine as hippuric acid.