Bethanechol is used to treat postoperative and neurogenic bladder atony. Which property allows bethanechol to produce a sustained muscarinic effect despite the presence of abundant acetylcholinesterase?
- A Its carbamate ester and beta-methyl group make it a poor substrate for acetylcholinesterase ✓
- B It irreversibly inhibits acetylcholinesterase
- C It is actively transported into the synaptic cleft away from the enzyme
- D It upregulates muscarinic receptors within hours of dosing
Correct answer: A. Its carbamate ester and beta-methyl group make it a poor substrate for acetylcholinesterase
Explanation
Bethanechol has a carbamate ester linkage plus a beta-methyl substituent on the choline moiety. The carbamate confers resistance to hydrolysis by acetylcholinesterase and the beta-methyl group shifts selectivity strongly toward muscarinic receptors, giving a sustained smooth muscle effect on the detrusor. Option B describes irreversible organophosphates, not bethanechol. Bethanechol is itself a direct agonist, so it needs no protection inside a synapse, and receptor upregulation is not a relevant acute mechanism.
Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.