OXYBUTYNIN CHLORIDE

Clinical safety rating: safe

Other anticholinergic drugs can have additive effects Can cause blurred vision and urinary retention.

How it works

Oxybutynin chloride is a competitive antagonist of muscarinic acetylcholine receptors (M1, M2, M3), leading to relaxation of the detrusor muscle and reduction of urinary bladder contractions.

What the body does with it

Metabolism	Extensively metabolized by CYP3A4 (primarily in liver and intestinal wall) to active metabolite N-desethyloxybutynin; also undergoes hydrolysis.
Excretion	Primarily hepatic metabolism; <0.1% excreted unchanged in urine. Metabolites (e.g., N-desethyloxybutynin) excreted mainly renally. Fecal elimination <0.02%.
Half-life	Terminal elimination half-life: 12–13 hours in plasma; clinical effect may persist longer due to active metabolite (N-desethyloxybutynin, half-life ~12–13 hours).
Protein binding	~91–93% bound to plasma proteins, primarily to alpha-1-acid glycoprotein and albumin.
Volume of Distribution	1.0 L/kg (range 0.8–1.3 L/kg) indicating extensive distribution into tissues.
Bioavailability	Oral immediate-release: ~6% (extensive first-pass metabolism). Oral extended-release: approximately 40% relative to immediate-release. Transdermal: approximately 9–12% systemic bioavailability.
Onset of Action	Immediate-release oral: 30–60 minutes. Extended-release oral: 3–6 hours. Transdermal: 24–48 hours.
Duration of Action	Immediate-release: 6–10 hours. Extended-release: up to 24 hours. Transdermal: approximately 96 hours (4 days) per patch.

Classification & Brands

Dosing & administration

5 mg orally 2-3 times daily; maximum 5 mg 4 times daily. Extended-release: 5-10 mg orally once daily; maximum 30 mg/day. Transdermal: 3.9 mg/day patch applied every 3-4 days. Topical gel: 1 g (100 mg) applied once daily.

Dosage form	SYRUP
Renal impairment	No specific dose adjustment for GFR ≥30 mL/min. For GFR <30 mL/min, use with caution; no standardized guidelines; consider reducing dose or frequency.
Liver impairment	Child-Pugh Class A: no adjustment. Child-Pugh Class B: use with caution; no specific dose reduction defined; consider lower starting dose. Child-Pugh Class C: contraindicated.
Pediatric use	Children >5 years: immediate-release 5 mg orally 2-3 times daily; maximum 5 mg 4 times daily. Extended-release: not recommended in children. Pediatric dosing based on weight not established.
Geriatric use	Start with lower dose (2.5 mg orally 2-3 times daily for immediate-release; 5 mg once daily for extended-release) due to increased anticholinergic sensitivity and risk of cognitive impairment. Titrate slowly. Avoid in frail elderly.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Other anticholinergic drugs can have additive effects Can cause blurred vision and urinary retention.

FDA category	Animal
Breastfeeding	Oxybutynin is excreted into breast milk in small amounts; M/P ratio unknown. Caution in breastfeeding due to potential anticholinergic effects in infant.
Teratogenic Risk	Pregnancy Category B. No evidence of fetal harm in animal studies; inadequate human studies. Use only if clearly needed.

Warnings & precautions

■ FDA Black Box Warning

No FDA black box warning.

Side Effect Profile

Common Effects	Dry mouth
Serious Effects

Absolute Contraindications

["Uncontrolled narrow-angle glaucoma","Urinary retention","Gastric retention","Known hypersensitivity to oxybutynin or any component of the formulation"]

Clinical Precautions

Precautions

["Exacerbation of narrow-angle glaucoma","Urinary retention and gastric retention (caution in patients with obstructive uropathy or GI obstructive disorders)","Decreased cognitive function (especially in elderly; may increase risk of dementia)","Heat prostration (risk of hyperthermia in hot environments due to decreased sweating)","Potential for CNS effects (sedation, dizziness, confusion)"]

Clinical Tips & Counseling

Drug interactions

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OXYBUTYNIN CHLORIDE

Clinical safety rating: safe

Other anticholinergic drugs can have additive effects Can cause blurred vision and urinary retention.

How it works

Oxybutynin chloride is a competitive antagonist of muscarinic acetylcholine receptors (M1, M2, M3), leading to relaxation of the detrusor muscle and reduction of urinary bladder contractions.

What the body does with it

Metabolism	Extensively metabolized by CYP3A4 (primarily in liver and intestinal wall) to active metabolite N-desethyloxybutynin; also undergoes hydrolysis.
Excretion	Primarily hepatic metabolism; <0.1% excreted unchanged in urine. Metabolites (e.g., N-desethyloxybutynin) excreted mainly renally. Fecal elimination <0.02%.
Half-life	Terminal elimination half-life: 12–13 hours in plasma; clinical effect may persist longer due to active metabolite (N-desethyloxybutynin, half-life ~12–13 hours).
Protein binding	~91–93% bound to plasma proteins, primarily to alpha-1-acid glycoprotein and albumin.
Volume of Distribution	1.0 L/kg (range 0.8–1.3 L/kg) indicating extensive distribution into tissues.
Bioavailability	Oral immediate-release: ~6% (extensive first-pass metabolism). Oral extended-release: approximately 40% relative to immediate-release. Transdermal: approximately 9–12% systemic bioavailability.
Onset of Action	Immediate-release oral: 30–60 minutes. Extended-release oral: 3–6 hours. Transdermal: 24–48 hours.
Duration of Action	Immediate-release: 6–10 hours. Extended-release: up to 24 hours. Transdermal: approximately 96 hours (4 days) per patch.

Classification & Brands

Dosing & administration

Dosage form	SYRUP
Renal impairment	No specific dose adjustment for GFR ≥30 mL/min. For GFR <30 mL/min, use with caution; no standardized guidelines; consider reducing dose or frequency.
Liver impairment	Child-Pugh Class A: no adjustment. Child-Pugh Class B: use with caution; no specific dose reduction defined; consider lower starting dose. Child-Pugh Class C: contraindicated.
Pediatric use	Children >5 years: immediate-release 5 mg orally 2-3 times daily; maximum 5 mg 4 times daily. Extended-release: not recommended in children. Pediatric dosing based on weight not established.
Geriatric use	Start with lower dose (2.5 mg orally 2-3 times daily for immediate-release; 5 mg once daily for extended-release) due to increased anticholinergic sensitivity and risk of cognitive impairment. Titrate slowly. Avoid in frail elderly.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Other anticholinergic drugs can have additive effects Can cause blurred vision and urinary retention.

FDA category	Animal
Breastfeeding	Oxybutynin is excreted into breast milk in small amounts; M/P ratio unknown. Caution in breastfeeding due to potential anticholinergic effects in infant.
Teratogenic Risk	Pregnancy Category B. No evidence of fetal harm in animal studies; inadequate human studies. Use only if clearly needed.

Warnings & precautions

■ FDA Black Box Warning

No FDA black box warning.

Side Effect Profile

Common Effects	Dry mouth
Serious Effects

Absolute Contraindications

["Uncontrolled narrow-angle glaucoma","Urinary retention","Gastric retention","Known hypersensitivity to oxybutynin or any component of the formulation"]