Toxicology
• Pyrethroids are synthetic derivatives of natural pyrethrins. Pyrethroids can be Type I(e.g., allethrin, resmethrin, D-phenothrin, and permethrin) or Type II (e.g., deltamethrin, cypermethrin, cyfluthrin and fenvalerate) based on symptoms of poisoning and chemical structure. Pyrethroids with a basic cyclopropane carboxylic ester structure are type I pyrethroids. The insecticidal activity of these synthetic pyrethroids was enhanced further by the addition of alpha-cyano (Type II ).
Type II pyrethroids may contain phenylacetic 3-phenoxybenzyl esters instead of the cyclopropane ring. Clinical signs of neurotoxicity in animals exposed to pyrethrins are similar to those of Type I pyrethroids . . .
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