Which medication stimulates bladder contractions to treat urinary retention?

• A. Tamsulosin
• B. Bethanechol
• C. Finasteride
• D. Oxybutynin

Answer: (B)

Stimulating bladder contractions requires a drug that acts as a muscarinic cholinergic agonist to increase detrusor muscle tone. Bethanechol directly activates muscarinic receptors in the bladder, especially the M3 receptors, causing the detrusor to contract and promote emptying. This makes it useful for non-obstructive urinary retention or retention after surgery or childbirth. By contrast, tamsulosin is an alpha-1 blocker that relaxes the bladder outlet and prostate to improve flow—not to stimulate contraction. Finasteride shrinks enlarged prostate over time but doesn’t acutely provoke bladder contractions. Oxybutynin is an antimuscarinic that reduces detrusor activity, used for overactive bladder rather than to relieve retention. So bethanechol is the best choice for increasing bladder contractions to treat urinary retention. Keep in mind potential cholinergic side effects (salivation, sweating, diarrhea, bradycardia) and that it’s avoided with mechanical obstruction or certain ulcers and asthma.