es of fabric impregnated with ¹⁴C-labeled permethrin were applied to the backs of rabbits for 1 week. The results showed that fabric treated with permethrin at a rate of 0.125 mg/cm² lost the substance to the skin surface at an average rate of 0.49% per day. At the end of 7 days, about 3.2% of the available permethrin had reached the skin, 2% having been recovered from the excreta (absorbed) and 1.2% remaining on the skin surface. Other variables, such as temperature, fabric type, sweat, and prelaundering, had little effect on migration rate (Snodgrass, 1992). Although the rabbit studies do not address the important issue of absorption of permethrin through the skin of humans from permethrin-impregnated cloth, they can be used to estimate the rate of transfer of permethrin from cloth to the skin. Although absorption of permethrin through the skin of humans and rabbits is likely to be much different, physical transfer of permethrin from cloth to skin should be similar.

A combination insecticide and repellent product (Hartz's Blockade) composed of 9% N,N-diethyl-m-toluamide (DEET) and 0.09% fenvalerate (a Type II pyrethroid insecticide) has been widely used for the control of fleas and other ectoparasites on dogs and cats. During 1987, the Illinois Animal Poison Information Center observed 200 times more poisonings in dogs or cats exposed to Blockade than to all other DEET-containing products. This report indirectly suggests that the use of DEET in combination with a pyrethroid insecticide increases the toxic response possibly by facilitating fenvalerate absorption (Dorman, 1990).

The possibility for enhancement of permethrin absorption by DEET is supported by a study on the use of DEET to enhance transdermal delivery of drugs. In in vitro diffusion studies using the hairless mouse skin as a barrier membrane, the absorption of a number of drugs (hydrocortisone, benzocaine, ibupropen, erythromycin, etc.) was studied (Windheuser et al., 1982). Although the diffusion cell results are not necessarily applicable to skin in vivo, they can demonstrate relative penetration enhancement. Enhancement of drug delivery is dramatic when DEET is present in the formulation. Drug diffusion, as expressed as a percent, increased from 1.6% to 35% for hydrocortisone and from not