DERMAL PENETRATION OF 4''-(EPI-METHYLAMINO)-4''-DEOXYAVERMECTIN B-1A BENZOATE IN THE RHESUS-MONKEY

The dermal absorption of the experimental avermectin insecticide emame ctin benzoate was studied in the Rhesus monkey. Dermal absorption was calculated by comparing radioactivity levels in excreta following derm al application of the compound with those following administration of an equivalent intravenous dose. After iv administration of 300 mu g [H -3]MAB1a (prepared as a 1:1 solution of propylene glycol:saline) to th ree monkeys, plasma levels decreased biphasically with a rapid decline in radioactivity during the first 15 min followed by a slower decline to background. By 7 days post-dose, approximately 90% and 5% of the a dministered radioactivity was recovered in the faeces and urine, respe ctively. After a washout period, 300 mu g [H-3]MAB1a (dissolved in emu lsifiable concentrate) was applied topically to the shaved forearm of the same monkeys. Following a IO-hr exposure period, approximately 90% of the radioactivity was recovered in a soap and water wash of the ex posed forearms. Although plasma radioactivity levels generally remaine d below background levels, approximately 1.5% of the applied dose was recovered in the excreta. Dermal absorption of [H-3]emamectin benzoate was calculated as 1.6%. The low dermal penetration of emamectin benzo ate indicates that minimal actual exposure of agricultural workers to this compound will occur. (C) 1997 Elsevier Science Ltd. All rights re served.