Brown_1988_J.Pharm.Sci_77_145

The metabolic fate of aprophen hydrochloride (2-diethylaminoethyl 2,2-diphenylpropionate) was studied in rats after intravenous administration. Both 14C-labeled and unlabeled aprophen were used in these studies. Blood samples were collected and analyzed to determine the identities of the metabolites formed. Utilizing high-performance liquid chromatography, desethylaprophen was identified as a major metabolite in ether-extracted samples from rats, and could be detected in blood samples 1 min after intravenous administration. It was most likely formed by N-de-ethylation of aprophen by a cytochrome P-450-dependent monooxygenase. Synthetic desethylaprophen was found to possess cholinolytic activity (i.e., it functioned as a muscarinic antagonist by blocking the contraction of acetylcholine-stimulated guinea pig ileum, the release of alpha-amylase from pancreatic acinar cells stimulated by carbachol, and also by inhibiting the binding of [3H]N-methyl scopolamine to the muscarinic receptors of guinea pig ileum). It was interesting that although the biological effects of desethylaprophen were 100-fold lower than those of aprophen, it was equally able to compete for the binding sites of muscarinic receptors of the guinea pig ileum.