Pharmacology · Overactive bladder agents
Oxybutynin !
The oldest antimuscarinic for the overactive and neurogenic bladder. It works well but often causes dry mouth, constipation and, in older adults, confusion.
Updated 2026-11-01
No structure of oxybutynin bound to its receptor exists. The figure shows tiotropium, another muscarinic antagonist, in the acetylcholine pocket of the rat M3 receptor, the subtype that contracts the bladder; the pocket is nearly identical in the human receptor.
Mechanism of action
Oxybutynin blocks the muscarinic action of acetylcholine on bladder smooth muscle and also has a direct antispasmodic effect on it. Fewer uninhibited detrusor contractions mean less urgency, frequency and leakage. It does not block skeletal neuromuscular junctions or autonomic ganglia. A metabolite, desethyloxybutynin, is also active.
- Blocks muscarinic receptors of the detrusor
- Also relaxes bladder smooth muscle directly
- Uninhibited contractions decrease
- Urgency, frequency and leakage ease
Pharmacokinetics
- Absorption
- Absorbed rapidly by mouth, but bioavailability is only about 6% because of first-pass metabolism; skin patch and gel forms avoid much of it
- Metabolism
- By CYP3A4 in the gut wall and liver, to the active desethyloxybutynin
- Half-life
- About 2 to 3 hours (immediate-release), longer in frail older adults
Indications
- Bladder instability in uninhibited or reflex neurogenic bladder (urgency, frequency, urge incontinence), including children from age five Neurogenic bladder →
- Overactive bladder Overactive bladder and urge incontinence →
Adverse effects
Common
- Dry mouth, very common
- Constipation
- Blurred vision
- Drowsiness and dizziness
- Less sweating
Contraindications
- Urinary retention
- Gastric retention and other severe slowing of gut movement
- Uncontrolled narrow-angle glaucoma
- Hypersensitivity to oxybutynin
Key interactions
- Strong CYP3A4 inhibitors (ketoconazole, clarithromycin, ritonavir, grapefruit juice)
- Higher oxybutynin levels; ketoconazole raised them about three to four times
- Other anticholinergic drugs
- More dry mouth, constipation and drowsiness
- Cholinesterase inhibitors for dementia (donepezil, rivastigmine)
- Opposite actions; each weakens the other
What is monitored
- Confusion or memory change, especially in the first months
- Post-void residual volume if retention is suspected
- Bowel habit
Administration and safety
- Tablets by mouth; extended-release forms are swallowed whole
- A lower starting dose is used in frail older adults, in whom the half-life is longer
Nursing care
- Teach sips of water or sugar-free gum for dry mouth
- Encourage fibre and fluids for constipation
- Warn about heat and exercise in hot weather
- Ask families to report new confusion in older adults
Pregnancy and breastfeeding
Safety in pregnancy is not established; it is given only when the benefit outweighs the risk.
Test yourself
Think of the answer, then tap the question to see it.
Why is oral oxybutynin's bioavailability low?
Extensive first-pass metabolism by CYP3A4 in the gut wall and liver.
Which patient group is most at risk of confusion with oxybutynin?
Older adults, especially those with cognitive impairment.
What is the most common side effect of oxybutynin?
Dry mouth.
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - OXYBUTYNIN CHLORIDE tablet (DailyMed (U.S. National Library of Medicine), 2026); Oxybutynin: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 11 (McGraw Hill, 2023); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.