Abstract

Abstract Metabolism of pyridalyl 2,6-dichloro-4-(3,3-dichloroallyloxy)phenyl 3-5-(trifluoromethyl)-2-pyridyloxypropyl ether was examined in male and female Sprague-Dawley rats. After a single oral administration of dichlorophenyl- 14 Cpyridalyl at 5 or 500 mg/kg, the 14 C concentration in blood reached maxima at 2 to 10 h and then decreased rapidly with a biological half-life of approximately 11 to 12 h. 14 C concentrations in liver, fat, adrenal gland, and spleen were relatively high at a low dose, reaching 2.3 to 2.7, 1.9 to 2.3, 1.1 to 1.9, and 1.4 ppm, respectively, in these tissues at 2 to 24 h after administration. Although 14 C elimination from fat and hair and skin was relatively slow compared with that from other tissues, the total residue on the 7th day was low, in the range of 1.3 to 2.3% of the dose. The 14 C distribution in tissues with a high dose, as examined by whole-body autoradiography, was similar to that observed for the low dose. Results revealed that more than 88% of the dosed radiocarbon was excreted within 1 day after administration, with cumulative 14 C excretion into urine and feces 7 days after administration of 1.7 to 2.6 and 98.7 to 101.7%, respectively. One urinary and fecal major metabolite (resulting from O -dealkylation) and two minor metabolites were identified by NMR and mass spectrometry. Residual 14 C in fat was extracted, and analysis by thin-layer chromatography showed it to be due to pyridalyl itself. No marked sex-related differences were observed in 14 C elimination, 14 C distribution, and metabolites.