Placental Transfer of Esfenvalerate and Fenvalerate in Pregnant Rats

Abstract

On a single oral dose or five consecutive oral doses of ¹⁴C-esfenvalerate [(S)-α-cyano-3-phenoxybenzyl (S)-2-(4-chlorophenyl)isovalerate] or ¹⁴C-fenvalerate [(RS)-α-cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)isovalerate] labeled in the acid moiety to 13-day pregnant rats at rates of 2.5 and 10mg/kg/day, respectively, the maternal blood and placenta generally showed higher ¹⁴C levels as compared with the fetus and amniotic fluid. Both compounds and their metabolites did not transfer readily from the maternal blood to the fetus, the amount of ¹⁴C transferred being less than 0.07% of the dose. There were no substantial differences in the fetal ¹⁴C level and the transfer ratio (¹⁴C tissue level/¹⁴C maternal blood level) between both labeled preparations. Major ¹⁴C-compounds in the fetus, maternal blood and placenta were the parent compounds, CPIA [2-(4-chlorophenyl) isovaleric acid] and CPIA-hydroxylated derivatives and there was no qualitative difference in metabolic fates between the two compounds, except that a trace amount of CPIA-cholesterol ester [cholesteryl (2R)-2-(4-chlorophenyl) isovalerate] was detected in the maternal blood and placenta only with fenvalerate. CPIA-cholesterol ester did not seem to transfer from the maternal blood to the fetus. Overall, esfenvalerate and fenvalerate seem to behave in the same manner as far as placental transfer was concerned.