This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Autonomic nervous system, Subject name: Pharmacology
Anticholinesterase inhibitor that binds to the anionic site is 
Select and explain. 
A. Physostigmine, B. Edrophonium, C. Neostigmine, D. Echothiophate
B: Edrophonium
Answer: B: Edrophonium 
Explanation: Neostigmine and pyridostigmine antagonize nondepolarizing neuromuscular blockade by increasing the availability of acetylcholine at the motor endplate, mainly by inhibition of acetylcholinesterase. They bind to esteric site. Edrophonium binds to anionic site. It has a more rapid onset of action but may be less effective than neostigmine in reversing the effects of nondepolarizing blockers in the presence of a profound degree of neuromuscular blockade Reference: Katzung Pharmacology; 13th edition; Chapter 8; Cholinoceptor-Blocking Drugs