Which drug is used to treat urinary retention in older male patients with BPH who are on antipsychotics?

Which drug is used to treat urinary retention in older male patients with BPH who are on antipsychotics?

• A. Pilocarpine
• B. Atropine
• C. Oxybutynin
• D. Bethanechol

Answer: (D)

When urinary retention stems from underactivity of the detrusor muscle, you want a drug that directly boosts bladder contractions to help empty the bladder. Bethanechol is a direct muscarinic (parasympathomimetic) agonist that increases detrusor smooth muscle tone, promoting voiding. It’s used for nonobstructive urinary retention and postoperative or neurogenic atony because it stimulates the muscle without relying on the sympathetic or central systems. In older men with BPH, there is often some level of obstruction, so treating retention must balance increasing detrusor contraction with the risk of worsening obstruction. Bethanechol is chosen here because it specifically enhances bladder contraction rather than relaxing the outlet, which would worsen retention if the obstruction is significant. It is more appropriate for a scenario where antipsychotics may contribute to anticholinergic urinary retention. Pilocarpine also activates muscarinic receptors but is used primarily for other indications (like glaucoma and dry mouth) and is not the standard choice for urinary retention. Atropine blocks muscarinic receptors and would worsen retention. Oxybutynin is an antimuscarinic that reduces bladder contractions and is used for overactive bladder, not retention. So, the best answer is the muscarinic agonist that directly stimulates the detrusor to contract, bethanechol.

When urinary retention stems from underactivity of the detrusor muscle, you want a drug that directly boosts bladder contractions to help empty the bladder. Bethanechol is a direct muscarinic (parasympathomimetic) agonist that increases detrusor smooth muscle tone, promoting voiding. It’s used for nonobstructive urinary retention and postoperative or neurogenic atony because it stimulates the muscle without relying on the sympathetic or central systems.

In older men with BPH, there is often some level of obstruction, so treating retention must balance increasing detrusor contraction with the risk of worsening obstruction. Bethanechol is chosen here because it specifically enhances bladder contraction rather than relaxing the outlet, which would worsen retention if the obstruction is significant. It is more appropriate for a scenario where antipsychotics may contribute to anticholinergic urinary retention.

Pilocarpine also activates muscarinic receptors but is used primarily for other indications (like glaucoma and dry mouth) and is not the standard choice for urinary retention. Atropine blocks muscarinic receptors and would worsen retention. Oxybutynin is an antimuscarinic that reduces bladder contractions and is used for overactive bladder, not retention.

So, the best answer is the muscarinic agonist that directly stimulates the detrusor to contract, bethanechol.