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

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

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

Answer: (C)

The main idea is how chemical stability against cholinesterases determines how long a drug lasts. Acetylcholine is rapidly broken down by acetylcholinesterase, so its half-life is very short. Methacholine is designed to be more resistant than acetylcholine, giving a longer action, but it’s still susceptible to hydrolysis. Carbachol has a carbamate-type linkage that makes it much less prone to acetylcholinesterase breakdown, so it remains active longer. Because of this reduced enzymatic degradation, carbachol tends to have the longest half-life among these three.

The main idea is how chemical stability against cholinesterases determines how long a drug lasts. Acetylcholine is rapidly broken down by acetylcholinesterase, so its half-life is very short. Methacholine is designed to be more resistant than acetylcholine, giving a longer action, but it’s still susceptible to hydrolysis. Carbachol has a carbamate-type linkage that makes it much less prone to acetylcholinesterase breakdown, so it remains active longer. Because of this reduced enzymatic degradation, carbachol tends to have the longest half-life among these three.