Bethanechol is preferred over methacholine for testing bladder detrusor function because:
- A Bethanechol has selective muscarinic M3 agonism and is resistant to acetylcholinesterase
- B Bethanechol is resistant to both acetylcholinesterase and butyrylcholinesterase, allowing a longer duration without systemic cardiovascular effects ✓
- C Bethanechol primarily acts on nicotinic receptors at the bladder ganglia
- D Methacholine causes excessive nicotinic receptor activation
Correct answer: B. Bethanechol is resistant to both acetylcholinesterase and butyrylcholinesterase, allowing a longer duration without systemic cardiovascular effects
Explanation
Bethanechol is a carbamate ester of beta-methylcholine. The carbamic acid ester bond is resistant to both acetylcholinesterase and butyrylcholinesterase (pseudocholinesterase), providing prolonged action suitable for bladder testing. Methacholine, while also resistant to acetylcholinesterase, is hydrolyzed by pseudocholinesterase and has more cardiovascular (M2) effects. Bethanechol does not selectively target M3 subtype over M2.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.