Anti-AChE potency

The OP insecticides, as discussed elsewhere in this book, have as a primary mechanism of acute toxicity the inhibition of the critical and widespread nervous system enzyme AChE. However, the anticholinesterase (anti-ChE) potencies do not correspond with the acute toxicity levels (Chambers et a ., 1990), indicating that metabolism is an important factor in determining the overall toxicity level. The OP insecticides evolved from the chemical technologies of World War II, which were used to develop the anti-ChE nerve agents. The OP inseeticidc.s bear some chemical resemblance to these nerve agents but are generally less toxic, often require metabolic activation to display anti-ChE activity and therefore are slower to act, and usually have more complex chemical substituents. 

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