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
Which of the following drug binds only with the anionic site of cholinesterase ? 
Select and explain. 
A. Physostigmine, B. Neostigmine, C. Edrophonium, D. Pyridostigmine
C: Edrophonium
Answer: C: Edrophonium 
Explanation: Physostigmine, neostigmine and pyridostigmine are carbamates by chemical nature, they bind to both esteritic as well as anionic site whereas edrophonium is an alcohol and binds to anionic site only.