Urinary incontinence drugs and mechanism
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AUA SUFU guideline overactive bladder pharmacotherapy antimuscarinic beta-3 agonist 2024
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Drugs used for urinary incontinence
Drug treatment depends on the type of incontinence. Medicines are mainly useful for urge incontinence due to overactive bladder (OAB). Stress incontinence is treated primarily with pelvic-floor therapy and, when needed, surgery.
| Type | Drug group and examples | Mechanism |
|---|---|---|
| Urge incontinence / OAB | Antimuscarinics: oxybutynin, tolterodine, solifenacin, darifenacin, fesoterodine, trospium | Block mainly M3 muscarinic receptors in detrusor smooth muscle. This inhibits acetylcholine-mediated involuntary detrusor contraction, causing detrusor relaxation, increased bladder capacity, and less urgency, frequency, and leakage. |
| Urge incontinence / OAB | Beta-3 agonists: mirabegron, vibegron | Stimulate beta-3 adrenergic receptors in the detrusor during bladder filling. This relaxes detrusor muscle and increases bladder storage capacity. |
| Stress urinary incontinence | Duloxetine | SNRI that raises serotonin and norepinephrine signaling in Onuf's nucleus in the sacral spinal cord. It increases pudendal-nerve activity and strengthens urethral sphincter contraction during increases in abdominal pressure. It is used for this indication in some countries, but not FDA-approved for stress incontinence in the US. |
| Overflow incontinence due to outlet obstruction, especially BPH | Alpha-1 blockers: tamsulosin, alfuzosin, doxazosin | Block alpha-1 receptors in the prostate and bladder neck, relaxing the outlet and improving bladder emptying. They treat the cause of overflow symptoms rather than directly improving sphincter weakness. |
| Neurogenic detrusor overactivity / refractory OAB | OnabotulinumtoxinA, injected into detrusor | Blocks presynaptic acetylcholine release at parasympathetic cholinergic nerve terminals. This reduces involuntary detrusor contractions. It may cause urinary retention and can require intermittent catheterization. |
| Selected overflow incontinence from an underactive bladder | Bethanechol, rarely used | Direct muscarinic agonist that increases detrusor contraction. Benefit is limited and adverse effects often restrict use. |
Key adverse effects and cautions
- Antimuscarinics: dry mouth, constipation, blurred vision, tachycardia, urinary retention, and possible cognitive adverse effects, especially in older adults. Avoid or use extreme caution in urinary retention and untreated narrow-angle glaucoma.
- Mirabegron: may raise blood pressure. Avoid in severe uncontrolled hypertension. It has fewer dry-mouth and constipation effects than antimuscarinics.
- Vibegron: similar beta-3 mechanism, with less concern for some drug interactions than mirabegron, though choice should be individualized.
- Duloxetine: nausea, insomnia, dizziness, fatigue, dry mouth, and discontinuation symptoms if stopped abruptly.
- Botulinum toxin: urinary tract infection and urinary retention are important risks.
Current AUA/SUFU guidance recommends offering either an antimuscarinic or beta-3 agonist for urgency, frequency, and urgency urinary incontinence from OAB, with selection based on adverse-effect profile and shared decision-making. The guideline also advises discussing potential cognitive risk when prescribing antimuscarinics. AUA/SUFU OAB guideline
Quick memory aid:
- Urge = relax the detrusor: antimuscarinics, beta-3 agonists, botulinum toxin.
- Stress = tighten the outlet: duloxetine, where approved.
- Overflow from obstruction = relax the outlet: alpha-1 blockers.
Textbook support: beta-3 agonists relax detrusor muscle and raise bladder capacity, while antimuscarinics reduce acetylcholine-driven detrusor contractions. Lippincott Illustrated Reviews: Pharmacology, Overactive Bladder section; Smith and Tanagho's General Urology, pharmacotherapy section.
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