Nowadays, organophosphorus poisoning is the most common emergency
throughout the world. Two functionally different types of drugs are used in common to
treat such intoxication cases. The first type includes the reactivators of
acetylcholinesterase (AChE)-oximes, which have the capability to restore the
physiological function of inhibited AChE. The second type includes anticholinergic,
such as atropine that antagonizes the effects of excessive ACh by blocking muscarinic
receptors. Alternatively, anticholinergic and reactivators may be co-administered to get
synergistic effects. At muscarinic and nicotinic synapses, organophosphorus
compounds inhibit AChE release by phosphoryl group deposition at the enzyme's
active site very quickly. AChE regenerative process can be accelerated by detaching
the OP compound at -OH group of the enzyme. OP compound combines with the
AChE enzyme forming a complex and making it inactive. After ageing of the inactive
state of AChE, it is difficult to break the complex to regenerate the enzyme resulting in
acetylcholine accumulation at synapses. To counter the effect of OP compound, oximes
catalyse the reactivation of active AChE by exerting nucleophilic attack on the
phosphoryl group. Oximes theoretically remove OP compound from the complex by
acting on phosphoryl bond resulting in enzyme reactivation. Reactivation of AChE
inhibited by OP compounds through the above mentioned approach poses certain
limitations. There is no universal antidote capable of effectively restoring AChE inhibited by wide-ranging OP compounds. The oxime reactivators are efficient only when
administered before the “ageing” of AChE-OP complex. Anticholinergic drugs, like
atropine, are effective only on muscarinic receptors but not on nicotinic receptors
(nAChRs).