For some time, compounds known as triaryl phosphates (eg, triorthocresyl phosphate) have been used as flame retardants, plasticizers, lubricating oils, and hydraulic fluids. They are weak cholinesterase inhibitors, but do inhibit “neurotoxic esterase” (NTE) present in the brain and spinal cord. A form of delayed neurotoxicity results from the inhibition of NTE. Triaryl phosphates have caused accidental poisonings in humans and other species (mostly cattle). Some OP insecticides (eg, PEN, leptophos) can also cause delayed neurotoxicity; however, field cases have been rare. The lesions associated with delayed neurotoxicity include demyelination of peripheral and spinal motor tracts due to loss of neurotoxic esterase function. Clinical signs associated with delayed neurotoxicity include muscle weakness and ataxia that progresses to flaccid paralysis. Signs are usually not manifest until 8–21 days after exposure to a neurotoxic triaryl phosphate. There are no specific antidotes.

Last full review/revision March 2012 by Ramesh C. Gupta, DVM, MVSc, PhD, DABT, FACT, FATS