On single oral administration of each of [1 R, traps]-, [1 RS, traps]-, [1 R, cis]-and [1 RS, cis]-tetramethrin[3, 4, 5, 6-tetrahydrophthalimidomethyl-(1 RS, trans/cis)-chrysanthemate] isomers labeled with 14C in the acid moiety to 13-day pregnant rats at 300 mg/kg, the radiocarbon was rapidly eliminated into the urine and feces, and almost completely recovered within 7 days. The 14C tissue residue levels were very low with the four labeled preparations. The major metabolic reactions for the

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... r isomers were cleavage of the ester linkage and oxidation at the isobutenyl group of the acid moiety. The traps isomers underwent ester cleavage to larger extents than the cis isomers. There were no significant differences in the 14C excretion, 14C tissue residue levels and the nature and amounts of metabolites between the [1 R]-and [1 RS]-traps isomers. The absorption in the gastrointestine, however, seemed to differ between the [1 R, cis]-and [1 RS, cis]-isomers, although once entering into the blood stream, the [1 R]-and [1 RS]-cis isomers appeared to receive the same matabolic fates. When 13-day pregnant rats were treated with single or 5 consecutive daily oral administrations of each of 14C-Neopynamin® (1 RS, traps/cis, 8/2) and Neopynamin Forte® (1 R, traps/ cis, 8/2) preparations labeled with 14C in the acid moiety at 300 mg/kg or 300 mg/kg/day, the radiocarbon transferred to the fetus were less than 0.004% of the dose and there were no significant differences in the 14C levels and the transfer ratio (14C tissue levels/14C maternal blood) for the fetus between the two preparations. Moreover, the major metabolites in the fetus and maternal blood with the two preparations were the same, and identified as chrysanthemic acids and their hydroxymethyl or carboxylic acid derivatives.