A patient on bethanechol for neurogenic bladder develops excessive muscarinic effects. Which receptor subtypes does bethanechol predominantly stimulate?

• A M1 and M3 only, with no effect on M2
• B M2 only, causing cardiac slowing with no bladder effect
• C N1 (ganglionic) and M3 simultaneously
• D M1, M2, and M3 non-selectively, with no nicotinic activity ✓

Explanation

Bethanechol is a synthetic choline ester that activates all muscarinic receptor subtypes (M1, M2, M3) but has no nicotinic activity and is resistant to acetylcholinesterase hydrolysis. M3 stimulation in the detrusor muscle promotes bladder contraction, while M2 stimulation reduces heart rate. Its lack of nicotinic activity makes it safer than carbachol for bladder atony treatment.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.