TY - JOUR T1 - Studies of metabolic pathways of trimebutine by simultaneous administration of trimebutine and its deuterium-labeled metabolite. JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 455 LP - 462 VL - 17 IS - 4 AU - Y Miura AU - S Chishima AU - S Takeyama Y1 - 1989/07/01 UR - http://dmd.aspetjournals.org/content/17/4/455.abstract N2 - Trimebutine maleate (I), (+-)-2-dimethylamino-2-phenylbutyl 3,4,5-trimethoxybenzoate hydrogen maleate, and a deuterium-labeled sample of its hydrolyzed metabolite, 2-dimethylamino-2-phenylbutanol-d3 (II-d3), were simultaneously administered to experimental animals at an oral dose of 10 or 50 mumol/kg, and distribution ratios of the two alternative initial metabolic steps, i.e., ester hydrolysis and N-demethylation, were estimated by determining the composition of the urinary alcohol-moiety metabolites, II, and its mono- and di-demethylated metabolites, III and IV, by GC/MS. In dogs, the order of quantities of the metabolites from II-d3 was II much greater than III much greater than IV, showing predominance of conjugation over N-demethylation. However, this order was reversed when the amounts of the metabolites from I were compared, indicating that I was preferentially metabolized by N-demethylation followed by ester hydrolysis and conjugation in this order. In rats, a considerable proportion of I was presumed to be metabolized by ester hydrolysis before N-demethylation. In in vitro experiments employing the liver microsomes and homogenates of liver and small intestine from rats and dogs, it was found that both ester-hydrolizing and N-demethylating activities were higher in rats than in dogs, and the conjugating activity was higher in dogs than in rats. It was also found that I, having a high lipophilicity, was more susceptible to N-demethylation than less lipophilic II. These results from the in vitro experiments could account for the species differences in the distribution ratio of the metabolic pathways of I in vivo. ER -