Human dose-excretion studies with pyrethroid insecticides cypermethrin and alphacypermethrin: relevance for...

1. Dose-excretion studies with cypermethrin (as a 1:1 cis/trans mixture) and alphacypermethrin (one of the two disastereoisomer pairs which constitute cis cypermethrin) were carried out with, in each case, two volunteers per dose level. The studies included (a) single oral alphacypermethrin doses of 0.25 mg, 0.50 mg and 0.75 mg followed by repeated alphacypermethrin doses at the same levels, daily for five days, (b) repeated oral cypermethrin doses of 0.25 mg, 0.75 mg and 1.5 mg daily for five days, and (c) a single dermal application of 25 mg cypermethrin to the forearm. Urine was monitored for the free and conjugated 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylic acid before and after dosing. 2. Metabolism and rate of excretion of a single oral dose of alphacypermethrin was similar to that of cis cypermethrin, on average, 43% of the dose was excreted as the cyclopropanecarboxylic acid in the first 24 h urine. There was no increase in urinary metabolite excretion when alphacypermethrin was administered as a repeated oral dose. Subjects excreted, on average, 49% of the dose as the cyclopropanecarboxylic acid in the subsequent 24 h periods after dosing. 3. There was no increase in the urinary cyclopropanecarboxylic acid excretion when cypermethrin was administered as a repeated oral dose. Subjects excreted, on average, 72% of the trans isomer dose and 45% of the cis isomer dose respectively in the subsequent 24 h periods after dosing. 4. Approximately 0.1% of the applied dermal dose of 25 mg cypermethrin was excreted within 72 h as the urinary cyclopropanecarboxylic acid. No conclusions can be drawn from such urinary excretion data as to the concentration of cypermethrin and its metabolites in the skin or other organs, or the possibility of other routes of metabolism or excretion.