A patient with overflow urinary incontinence due to an acontractile detrusor after spinal cord injury is started on bethanechol. The treating physician chooses bethanechol over methacholine specifically because of one pharmacokinetic property. What is this property?
- A Bethanechol has much higher potency allowing lower doses with fewer systemic effects
- B Bethanechol is resistant to hydrolysis by both acetylcholinesterase and plasma cholinesterase due to its carbamate structure, providing a longer duration of action ✓
- C Bethanechol crosses the blood-brain barrier and has central muscarinic action to reinforce micturition reflex
- D Bethanechol selectively activates M3 receptors in the bladder without affecting M2 receptors elsewhere
Correct answer: B. Bethanechol is resistant to hydrolysis by both acetylcholinesterase and plasma cholinesterase due to its carbamate structure, providing a longer duration of action
Explanation
Bethanechol is a synthetic choline ester that, unlike acetylcholine or methacholine, is not hydrolyzed by acetylcholinesterase or butyrylcholinesterase (plasma cholinesterase). The carbamate group replaces the ester linkage seen in ACh, making it resistant to cholinesterase-mediated degradation. This confers a longer duration of action (typically 1-2 hours orally). Additionally, the beta-methyl group reduces muscarinic effects on the cardiovascular system, making it useful specifically for urinary retention and GI atony.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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