Metabolism of the <i>cis</i>‐ and <i>trans</i>‐isomers of cypermethrin in mice

Abstract

Abstract Metabolism in mice of the separated cis ‐ and trans ‐isomers of the pyrethroid insecticide cypermethrin (NRDC 149), ( RS )‐α‐cyano‐3‐phenoxybenzyl (1 RS )‐ cis , trans ‐3‐(2,2‐dichlorovinyl)‐2,2‐dimethylcyclopropanecarboxylate, was investigated in each case with preparations that were 14 C‐labelled in the benzyl and cyclopropyl moieties. Radioactivity from the trans ‐isomer was mainly excreted in the urine and that from the cis ‐isomer in the faeces. Elimination of both isomers was rapid except for a small portion (approximately 2%) of the cis ‐isomer which was released from the fat with a half‐life of approximately 13 days. Metabolism of cypermethrin occurred mainly by ester cleavage and elimination of the cis ‐ and trans ‐3‐(2,2‐dichlorovinyl)‐2,2‐dimethyl‐ cyclopropanecarboxylic acid moieties as glucuronide conjugates. The α‐cyano‐3‐phenoxybenzyl alcohol released by ester cleavage was mainly converted to 3‐phenoxy‐benzoic acid which was partly eliminated unchanged, partly conjugated with aminoacids (mainly taurine) and glucuronic acid, and partly oxidised to 3‐(4‐hydroxyphenoxy) benzoic acid which was excreted as the sulphate conjugate. Metabolites retaining the ester linkage were formed by hydroxylation at various sites in the molecule with more hydroxylation of the cis ‐ than of the trans ‐isomer occurring.