Organophosphates and Carbamates

Organophosphates (OPs) are a major class of insecticides. Their acute toxicity is due to inhibition of the enzyme acetylcholinesterase (AChE) resulting in the accumulation of acetylcholine in the synapse, with an ensuing cholinergic crisis. Treatment of OP intoxication consists in administering atropine, to block muscarinic receptors, and oximes, to facilitate the reactivation of AChE. An intermediate syndrome, characterized by muscular weakness, is at times observed in humans after OP poisoning. Some OPs can also cause a peripheral neuropathy (OP-induced delayed polyneuropathy) that is seen weeks after acute poisoning when all other symptoms have subsided, and is unrelated to AChE inhibition. Another class of insecticides that act by inhibiting AChE is that of carbamates; the signs and symptoms of intoxication are the same as for OPs, but of much shorter duration.