Oxybutynin

Generic Name

Oxybutynin hydrochloride

Brand Names

Ditropan

Ditropan XL

Oxytrol

Lyrinel XL

Kentera

Gelnique

Anturol

Urotrol

Various generics are available in immediate-release (IR) tablets, extended-release (ER) tablets, transdermal patches, and topical gel formulations

Drug Class

Antimuscarinic agent

Anticholinergic

Urinary antispasmodic

Mechanism of Action

Oxybutynin is a competitive antagonist of acetylcholine at muscarinic receptors (primarily M1 and M3 subtypes) in smooth muscle

It exerts direct antispasmodic effects on detrusor muscle in the bladder

By inhibiting involuntary contractions, it increases bladder capacity, reduces urgency, frequency, and incontinence episodes

Also has local anesthetic and direct muscle relaxant properties

Metabolized to N-desethyloxybutynin (active metabolite) which contributes significantly to its efficacy and side effects

ER formulations provide controlled release and lower peak plasma levels, reducing anticholinergic side effects

Indications

Approved Indications

Overactive bladder (OAB) with symptoms of:

– Urinary frequency

– Urgency

– Urge incontinence

Neurogenic detrusor overactivity (e.g., in multiple sclerosis, spinal cord injury)

Nocturia or nocturnal enuresis (off-label in children)

Bladder spasms following urological surgery or catheterization

Off-Label Uses

Hyperhidrosis (excessive sweating)

Urinary incontinence in Parkinson’s disease

Nocturia in elderly

Diarrhea associated with irritable bowel syndrome (IBS)

Palliative use to reduce excessive secretions

Dosage and Administration

Adults

Immediate-Release Tablets (Ditropan)

Start: 2.5–5 mg orally two to three times daily

Max: 20 mg/day (divided doses)

Adjust dose based on response and tolerability

Extended-Release Tablets (Ditropan XL)

Start: 5–10 mg once daily

Titrate in 5 mg increments at weekly intervals

Max: 30 mg/day

Do not crush or chew ER tablets

Transdermal Patch (Oxytrol)

Delivers 3.9 mg/day

Apply one patch twice weekly (every 3–4 days) to abdomen, hip, or buttock

Rotate sites to avoid skin irritation

Topical Gel (Gelnique, Anturol)

1 g of gel delivers 1 mg oxybutynin

Apply once daily to dry, intact skin on abdomen, thighs, or upper arms

Avoid application to the same site consecutively

Wash hands after use to prevent transfer to eyes or mouth

Pediatrics

Children >5 years (neurogenic bladder)

IR tablets: Start at 0.2 mg/kg/dose 2–3 times daily

Max: 5 mg per dose, 20 mg/day

ER tablets: Approved for children ≥6 years

Start: 5 mg once daily

Max: 15 mg/day

Administration Notes

IR tablets can be taken with or without food

ER tablets should be swallowed whole

Patches and gels avoid first-pass metabolism and reduce systemic side effects

Pharmacokinetics

Absorption

Well absorbed orally

Bioavailability: 6% (IR), 30% (ER)

Gel and patch have slower absorption and steadier plasma levels

Distribution

Widely distributed

Crosses the blood-brain barrier

High tissue affinity, especially in bladder smooth muscle

Metabolism

Hepatic metabolism via CYP3A4

Major metabolite: N-desethyloxybutynin (active)

Elimination

Renal and fecal excretion

Half-life:

– IR: ~2–3 hours

– ER: ~13 hours

– Transdermal: steady levels over 3–4 days

Contraindications

Urinary retention

Gastric retention or paralytic ileus

Severe decreased gastrointestinal motility

Uncontrolled narrow-angle glaucoma

Hypersensitivity to oxybutynin or any formulation component

Warnings and Precautions

CNS Effects

May cause confusion, hallucinations, sedation, and memory impairment especially in elderly

Monitor closely in patients with dementia or those using centrally acting drugs

Heat Intolerance and Hyperthermia

Reduces sweating

Risk of heat stroke in hot environments

Advise hydration and avoid overheating

Angioedema and Anaphylaxis

Rare, but serious hypersensitivity reactions reported

Urinary Retention and Outflow Obstruction

Caution in patients with bladder outlet obstruction

May exacerbate retention

Gastrointestinal Disorders

May worsen gastroesophageal reflux or cause paralytic ileus

Caution in patients with GERD or motility disorders

Ocular Effects

May increase intraocular pressure

Use cautiously in patients at risk of glaucoma

Pregnancy and Lactation

Pregnancy Category B

No evidence of harm in animal studies

Use only if clearly needed during pregnancy

No controlled studies in pregnant women

Lactation

Unknown if excreted in breast milk

Use caution, especially in nursing infants with GI sensitivity

Pediatric Use

Approved for use in neurogenic bladder in children ≥5 years

ER tablets used in children ≥6 years

Safety in younger children not established

Geriatric Use

Increased risk of CNS side effects including confusion

Start at lower doses and monitor mental status

Adverse Effects

Very Common

Dry mouth (up to 80%)

Constipation

Headache

Dizziness

Common

Blurred vision

Nausea

Drowsiness

Dry eyes

Urinary retention

Flushing

Confusion (elderly)

Uncommon

Tachycardia

Hallucinations

Delirium

Skin rash (patch users)

Application site irritation (topical use)

Rare

Anaphylaxis

Angioedema

Severe cognitive decline in dementia

Overdose

Symptoms

Agitation

Tachycardia

Seizures

Urinary retention

Flushing

Paralytic ileus

CNS depression or excitation

Management

Supportive care

Activated charcoal if early ingestion

Physostigmine may reverse severe anticholinergic toxicity

Benzodiazepines for seizures

Hydration and monitoring of vital signs

Drug Interactions

CYP3A4 Inhibitors (e.g., ketoconazole, clarithromycin, ritonavir)

May increase plasma levels of oxybutynin

Monitor for enhanced anticholinergic effects

CNS Depressants (e.g., alcohol, sedatives, benzodiazepines)

Additive CNS depression

Monitor mental status

Other Anticholinergics (e.g., atropine, tolterodine, diphenhydramine)

Additive antimuscarinic effects

Risk of constipation, dry mouth, urinary retention, cognitive impairment

Cholinesterase Inhibitors (e.g., donepezil)

Opposing actions may reduce efficacy of both drugs

Use caution in dementia patients

Metoclopramide

Opposes prokinetic effect

Avoid concomitant use

Potassium Chloride (oral solid)

Increased risk of GI ulceration

Avoid use together if possible

Use in Special Populations

Renal Impairment

No major dose adjustments

Monitor anticholinergic toxicity in advanced disease

Hepatic Impairment

Start at low doses

ER and topical forms may be safer due to reduced first-pass effect

Monitoring Parameters

Improvement in urinary frequency, urgency, incontinence

Bowel function (monitor for constipation)

Mental status (especially in elderly)

Vision changes (blurred vision, dry eyes)

Skin reactions with transdermal use

Signs of urinary retention

Formulations Available

Immediate-Release Tablets

5 mg tablets (twice to three times daily)

Extended-Release Tablets (Ditropan XL, Lyrinel XL)

5 mg, 10 mg, 15 mg once daily

Transdermal Patch (Oxytrol)

Delivers 3.9 mg/day, changed every 3–4 days

Topical Gel (Gelnique, Anturol)

1 mg/g gel, applied once daily

Oral Syrup

5 mg/5 mL, used in pediatrics or dysphagia

Comparative Pharmacology

Oxybutynin vs Tolterodine

Oxybutynin has more CNS side effects due to higher lipophilicity

Tolterodine may be better tolerated in elderly

Oxybutynin vs Solifenacin

Solifenacin is more selective for M3 receptors, fewer CNS effects

Oxybutynin has more data in pediatrics and neurogenic bladder

Oxybutynin vs Mirabegron

Mirabegron (β3 agonist) is not anticholinergic

Preferred in patients at risk for cognitive impairment

Oxybutynin vs Fesoterodine

Fesoterodine is better tolerated, especially in extended-release form

Regulatory and Legal Status

Prescription-only medication

Approved worldwide for OAB and neurogenic bladder

Oxytrol for Women available OTC in the USA (transdermal patch only)

Listed in BNF, FDA Orange Book, MIMS