Which medication stimulates detrusor muscle contraction?

• A. Bethanechol
• B. Atropine
• C. Prazosin
• D. Neostigmine

Answer: (A)

Detrusor contraction during voiding is driven by parasympathetic stimulation releasing acetylcholine onto muscarinic receptors on the bladder wall, especially M3 receptors. Bethanechol is a direct muscarinic agonist, so it binds those receptors on the detrusor and triggers contraction, promoting bladder emptying. This direct stimulation makes it the best choice when you want to promote detrusor activity. In contrast, atropine blocks muscarinic receptors and would reduce contraction; prazosin is an alpha-1 blocker affecting outlet resistance rather than stimulating the detrusor, and neostigmine increases acetylcholine indirectly by inhibiting acetylcholinesterase, which can enhance contraction but is less specific for detrusor stimulation.