ACHE and organophosphate poisoning: Although of similar chemical structure, unlike organophosphates, which bind irreversibly, and carbamates, which bind reversibly for 8 to 10 hours, rivastigmine binds acetylcholinesterase for only 4 to 6 hours.15 Similar to the treatment with acetylcholinesterase inhibitors, in organophosphate poisoning, the resultant increase in central cholinergic tone consequent to the imbalance between acetylcholine and dopamine in the substantia nigra and basal ganglia lead to EPS symptoms.