Refer to the biochemistry in focus section of your text for this chapter to answer this question. sarin inhibits acetylcholinesterase by covalently modifying the enzyme active site. pyridostigmine is a competitive inhibitor of acetylcholinesterase and can serve as an antidote for sarin poisoning. how does pyridostigmine prevent sarin from inhibiting acetylcholinesterase? pyridostigmine binds to sarin and prevents it from binding to and modifying the enzyme active site. pyridostigmine reverses the covalent modification caused by sarin in the acetylcholinesterase active site.