A 35-year-old man with known myasthenia gravis is prescribed bethanechol for neurogenic bladder. What is the mechanistic basis by which bethanechol is preferred over other cholinomimetics in this setting?

• A Bethanechol stimulates nicotinic receptors at the autonomic ganglia without muscarinic effects
• B Bethanechol is the only cholinomimetic that crosses the blood–brain barrier to act centrally on micturition centres
• C Bethanechol acts selectively on M3 muscarinic receptors of the detrusor and is resistant to acetylcholinesterase hydrolysis ✓
• D Bethanechol enhances release of endogenous acetylcholine from parasympathetic nerve terminals

Explanation

Bethanechol is a synthetic muscarinic agonist with two important properties: it is selective for muscarinic receptors (especially M3 which mediates detrusor contraction), and the carbamate ester linkage makes it highly resistant to hydrolysis by acetylcholinesterase, giving it a longer duration of action. It has negligible nicotinic effects and does not cross the blood–brain barrier. These properties make it suitable for stimulating the urinary bladder without the systemic toxicity and short duration of acetylcholine.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.