Which medication is a muscarinic agonist used to stimulate detrusor muscle contraction?

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

Answer: (A)

Stimulation of the detrusor muscle to promote urination is achieved by activating muscarinic receptors, especially the M3 subtype, on the bladder. Bethanechol is a direct muscarinic agonist that resists acetylcholinesterase, so it reliably activates these receptors and causes detrusor contraction, helping to empty the bladder. It’s used clinically for postoperative or neurogenic urinary retention when the bladder is underactive. Other options don’t fit: atropine blocks muscarinic receptors, which would inhibit detrusor contraction and worsen retention; prazosin blocks alpha-1 receptors and primarily affects sphincter tone rather than directly stimulating the detrusor; epinephrine acts on adrenergic receptors and tends to relax the detrusor via beta effects, not promote contraction. So bethanechol best accomplishes the goal of stimulating detrusor contraction.