This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Shoest acting anticholinesterase is ? 
Select and explain. 
A. Edrophonium, B. Pyridostigmine, C. Glycopyrrolate, D. Neostigmine
A: Edrophonium
Answer: A: Edrophonium 
Explanation: Ans. is 'a' i.e., Edrophonium Edrophonium is the shoest acting anti-ChE. When carbamates (other than edrophonium) and organophophates react with cholinesterase, they form covalent bond at esteratic site, which is considerably resistant to hydrolysis. In contrast, edrophonium binds electrostatically and by hydrogen bonds at anionic site (not at esteratic site) of cholinesterase. The enzyme inhibitor complex does not involve a covalent bond and is correspondingly sho lived (2-10 minutes). So edrophonium is also called as noncovalent inhibitor.