Metabolism of imiprothrin isomers in rats: Biotransformation and excretion

The biotransformation and excretion of imiprothrin ([2,5-dioxo-3-(2-propynyl)-1-imidazolidinyl]methyl (1R)-cis, trans-chrysanthemate), a novel pyrethroid, was examined by dosing (1R)-trans- or (1R)-cis-[imidazolidinyl-5- 14 C]imiprothrin orally to male and female rats at 1 (low dose) and 200 mg/kg (high dose). Elimination of the trans- and cis-isomers was rapid, and almost all of the dosed 14 C was excreted into urine, feces and expired air within 7 days, with the former route predominating (more than 83% of the dosed 14 C). 14 C-Tissue residues on the 7th day after administration were generally low in all dosed groups. There were no marked sex-related differences in the rate of 14 C-excretion and the 14 C-tissue residues within either treatment group. To elucidate metabolic pathways of imiprothrin, major urinary metabolites were isolated using (1R)-cis-[imidazolidinyl-5- 14 C]imiprothrin and chromatographic techniques, with identification by spectroanalyses (NMR and MS). Metabolites in urine or feces were also identified and quantified by HPLC analyses using these isolated metabolites as standards. No marked sex-related differences in the metabolite profiles were observed within dose groups. Based on the identified metabolites, the main metabolic reactions of imiprothrin in rats are 1) cleavage of the ester linkage, 2) cleavage of the imidomethylene linkage, 3) hydroxylation of the imidazolidine ring, 4) dealkylation of the 2-propynyl group and 5) oxidation at the ω-trans-methyl group in the isobutenyl side chain.