Dermal absorption of the insect repellent deet (N,N‐diethyl‐m‐toluamide) in rats and monkeys: Effect of anatomical site and multiple exposure

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Abstract
The dermal absorption of 14C‐ring‐labeled DEET (N,N‐diethyl‐m‐toluamide) applied in acetone to the skin of Sprague‐Dawley rats and rhesus monkeys for 24 h was determined. Absorption in rats dosed middorsally was 36 ± 8% with a urinary excretion half‐life (t 1/2) of 20 h. Both the extent and rate of absorption in monkeys were highly dependent on anatomic site, with 14 ± 5% (t 1/2 = 4 h) penetrating the forearm, 33 ± 11% (t 1/2 = 6 h) the forehead, 27 ± 3% (t 1/2 = 7 h) the dorsal forepaw, and 68 ± 9% (t 1/2 = 8 h) the ventral forepaw. Since DEET is commonly applied frequently by the same individual, the effect of multiple exposure was investigated. No significant difference (p ≥ .3) was obtained either between the total percentage absorbed dermally with single (36 ± 8%; t 1/2 = 20 h) as compared with three (31 ± 5%; t 1/2 = 76 h) DEET applications at 2‐h intervals to rats, or between single (14 + 5%; t 1/2 = 4 h) as compared with three (12 ± 1%; t 1/2 = 4 h) applications at 0.5‐h intervals to monkey forearm. A DEET metabolite detected in urine 4 h following topical exposure in humans was extractable following either acid (HCI) hydrolysis or urine treatment with β‐glucuronidase and was identified as ethyltoluamide (parent ion 163; base ion 119) following HPLC purification and characterization by GC/MS.

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