Which statement about methacholine is true?

Which statement about methacholine is true?

• A. Methacholine is 3 times more stable than acetylcholine.
• B. Methacholine is less stable than acetylcholine.
• C. Methacholine is equally stable as acetylcholine.
• D. Methacholine is rapidly hydrolyzed by esterases.

Answer: (C)

Stability and duration of action for cholinergic agonists depend on resistance to acetylcholinesterase. Acetylcholine is rapidly hydrolyzed by AChE, so its effects are very brief. Methacholine is a synthetic choline ester designed to resist AChE, so it remains active longer. The idea that it is about three times more stable than acetylcholine captures this increased resistance to enzymatic breakdown. It isn’t less stable, nor is it equally stable, and while it is eventually hydrolyzed, its longer-lasting action comes from its reduced susceptibility to hydrolysis.

Stability and duration of action for cholinergic agonists depend on resistance to acetylcholinesterase. Acetylcholine is rapidly hydrolyzed by AChE, so its effects are very brief. Methacholine is a synthetic choline ester designed to resist AChE, so it remains active longer. The idea that it is about three times more stable than acetylcholine captures this increased resistance to enzymatic breakdown. It isn’t less stable, nor is it equally stable, and while it is eventually hydrolyzed, its longer-lasting action comes from its reduced susceptibility to hydrolysis.