Cholinesterase inhibitor

Cholinesterase inhibitors (ChEIs), also known as anti-cholinesterase, are chemicals that prevent the breakdown of the neurotransmitter acetylcholine or butyrylcholine. This increases the amount of the acetylcholine or butyrylcholine in the synaptic cleft that can bind to muscarinic receptors, nicotinic receptors and others. This group of inhibitors is divided into two subgroups, acetylcholinesterase inhibitors (AChEIs) and butyrylcholinesterase inhibitors (BChEIs).
ChEIs may be used as drugs for Alzheimer's and myasthenia gravis, and also as chemical weapons and insecticides. Side effects when used as drugs may include loss of appetite, nausea, vomiting, loose stools, vivid dreams at night, dehydration, rash, bradycardia, peptic ulcer disease, seizures, weight loss, rhinorrhea, salivation, muscle cramps, and fasciculations.
ChEIs are indirect-acting parasympathomimetic drugs.
It came to light during the Berlin Charité hospital treatment for poisoning of Russian dissident Alexei Navalny that a nerve agent known as belonging to the Novichok agents is a ChEI.
Since November 2019 the group of ACheIs known as "Novichoks" have been banned as agents of warfare under the Chemical Weapons Convention. Novichok agents are neurotoxic organophosphorus compounds and are considered more potent than VX gas, also a neurotoxic organophosphorus compound.
Medical use.
While 4 ChEIs are approved in the US for the treatment of Alzheimer's Disease, only three of these are available commercially. The three available are rivastigmine, donepezil, and galantamine, while tacrine is not. They are generally used to treat Alzheimer's disease and dementia. If a benefit occurs, it is generally during the second or third month after starting.
It is difficult to determine which ChEI has greater efficacy, due to design flaws in head-to-head comparison studies.
Pyridostigmine is used in the treatment of myasthenia gravis. 
Cholinesterase inhibitor toxicity.
Common side effects of one ChEI include insomnia, nausea and vomiting, accidental injury, headache, dizziness, bradycardia, hypotension, ecchymosis, and sleep disturbance.
Binding affinity.
Acetylcholinesterase inhibitors.
Donepezil, phenserine, huperzine A, and BW284c51 are selective AChE inhibitors.
Butyrylcholinesterase inhibitor.
Tetra (monoisopropyl) pyrophosphoramide (Iso-OMPA) and ethopropazine are selective BChE inhibitors.
AChE and BChE inhibitor.
Paraoxon and rivastigmine are both acetylcholinesterase inhibitors and butyrylcholinesterase inhibitors.
In 2015, the United States Food and Drug Administration's Adverse Event Reporting System database compared rivastigmine to the other ChEI drugs donepezil and galantamine found that rivastigmine was associated with a higher frequency of reports of death as an adverse event.
Acetylcholinesterase inhibitors and nicotinic receptor modulator.
Galantamine might be less well tolerated than donepezil and rivastigmine.