Oxybutynin
An antimuscarinic that relaxes the bladder's detrusor muscle, used for overactive bladder with urgency, frequency and urge incontinence.
Drug card
- Class
- Antimuscarinic
- How it works
- Blocking muscarinic receptors, so parasympathetic effects are switched off
- Used for
- Overactive bladder with urgency and urge incontinence
- Neurogenic detrusor overactivity in children
- Known for
- Dry mouth
- Confusion, agitation or hallucinations
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does oxybutynin work?
A tertiary amine that blocks muscarinic receptors on bladder smooth muscle and also relaxes that muscle directly, so the detrusor contracts less and the bladder holds more urine. The R-isomer carries most of the antimuscarinic action, and the metabolite desethyloxybutynin is active too. It has central effects, so drowsiness and confusion can occur.
Like other antimuscarinics: They occupy muscarinic acetylcholine receptors without activating them, competitively blocking the acetylcholine released by parasympathetic nerves. The heart speeds up, glands dry up, the smooth muscle of the gut, bladder and airways relaxes, and the pupil dilates and stops focusing. Tertiary amines such as atropine enter the brain; quaternary ones such as hyoscine butylbromide do not.
Uses
What is oxybutynin used for?
- Overactive bladder with urgency and urge incontinence
- Neurogenic detrusor overactivity in children
Side effects
Side effects of oxybutynin
- Dry mouthKnown for
- Confusion, agitation or hallucinationsKnown forSerious
- Constipation
- Drowsiness
- Dizziness
- Headache
- Blurred vision and dry eyes
- Diarrhea
- Indigestion and nausea
- Urinary retentionSerious
- Heat prostration from reduced sweatingSerious
- Angioedema of the face, lips or throatSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Contraindicated in urinary retention, gastric retention and uncontrolled narrow-angle glaucoma.
- Dementia, Parkinson's disease or myasthenia gravis: it can make symptoms worse.
- Hot weather or fever: reduced sweating can lead to heat prostration.
- Other anticholinergic drugs add to its effects; strong CYP3A4 inhibitors such as ketoconazole raise its levels.
Good to know: When bladder antimuscarinics do not suit, mirabegron, a beta-3 agonist, relaxes the bladder in a different way.
Remember it
A way to remember it
Hot as a hare, dry as a bone, red as a beet, blind as a bat, full as a flask.
The classic signs of too much antimuscarinic effect: overheating because sweating stops, a dry mouth and skin, flushing, blurred vision from a wide pupil that cannot focus, and a full bladder from urinary retention. Confusion often comes with them.
A mnemonic widely used in teaching
Its class
Antimuscarinics
Other antimuscarinics with a card:
Easily mixed up with direct-acting muscarinic agonists, anticholinesterases and beta-3 agonists.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Oxybutynin chloride extended-release tablets: label (DailyMed)
- Side effects of oxybutynin (NHS)
- Common questions about oxybutynin (NHS)
- Oxybutynin (NCI Thesaurus)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Autonomic nervous system
Oxybutynin is one of 10 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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