Which compound has the shortest half-life among Acetylcholine, Carbachol, and Methacholine?

Which compound has the shortest half-life among Acetylcholine, Carbachol, and Methacholine?

• A. Carbachol
• B. Acetylcholine
• C. Methacholine
• D. Bethanechol

Answer: (B)

The key idea is how quickly each agent is broken down by acetylcholinesterase. Acetylcholine is rapidly hydrolyzed by this enzyme in synapses, giving it an extremely short half-life. The other cholinergic agonists—carbachol and methacholine—are designed to resist acetylcholinesterase, so they persist longer and have longer durations of action. Bethanechol is also resistant to AChE, with an even longer action in some tissues. Therefore, among these options, acetylcholine has the shortest half-life because it is degraded almost immediately by acetylcholinesterase.

The key idea is how quickly each agent is broken down by acetylcholinesterase. Acetylcholine is rapidly hydrolyzed by this enzyme in synapses, giving it an extremely short half-life. The other cholinergic agonists—carbachol and methacholine—are designed to resist acetylcholinesterase, so they persist longer and have longer durations of action. Bethanechol is also resistant to AChE, with an even longer action in some tissues. Therefore, among these options, acetylcholine has the shortest half-life because it is degraded almost immediately by acetylcholinesterase.