OXYTROL FOR WOMEN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for OXYTROL FOR WOMEN (OXYTROL FOR WOMEN).
Oxybutynin is a competitive antagonist of muscarinic acetylcholine receptors (M1, M2, M3 subtypes), primarily blocking M3 receptors in the detrusor muscle of the bladder, thereby reducing involuntary detrusor contractions and increasing bladder capacity.
| Metabolism | Extensively metabolized by cytochrome P450 (CYP) 3A4 in the liver and intestinal wall to active metabolite N-desethyloxybutynin, which also has antimuscarinic activity; undergoes further metabolism via CYP3A4 and other pathways. |
| Excretion | Primarily hepatic metabolism; renal excretion accounts for <1% as unchanged drug; biliary excretion of metabolites is minimal; approximately 70-80% of a dose is excreted in urine as metabolites. |
| Half-life | Terminal elimination half-life is approximately 2.7 hours (range 2-3 hours); clinical context: frequent dosing may be required due to short half-life. |
| Protein binding | Approximately 50% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Approximately 1.3 L/kg; indicates extensive distribution into tissues. |
| Bioavailability | Transdermal: approximately 80-85% relative to intravenous administration; oral: low and variable (approximately 6%) due to extensive first-pass metabolism. |
| Onset of Action | Transdermal: clinical effect begins within 4-8 hours after initial application; systemic absorption is gradual. |
| Duration of Action | Transdermal patch provides sustained delivery over 7 days; clinical effect persists for the duration of patch wear; after patch removal, effects decline over 12-24 hours. |
One transdermal system (oxybutynin 3.9 mg/day) applied to the abdomen, hip, or buttock twice weekly (every 3 to 4 days).
| Dosage form | FILM, EXTENDED RELEASE |
| Renal impairment | No dosage adjustment required for mild to moderate renal impairment (CrCl ≥30 mL/min). Contraindicated in severe renal impairment (CrCl <30 mL/min) due to lack of safety data. |
| Liver impairment | Contraindicated in severe hepatic impairment (Child-Pugh class C). No formal dose adjustments established for mild to moderate impairment; use with caution. |
| Pediatric use | Not approved for pediatric use. Safety and efficacy in patients <18 years have not been established. |
| Geriatric use | Initiate with same dose as adults (3.9 mg/day). Consider increased sensitivity and risk of anticholinergic side effects; monitor cognitive function and constipation. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for OXYTROL FOR WOMEN (OXYTROL FOR WOMEN).
| Breastfeeding | Excretion of oxybutynin in human milk has not been studied; however, minimal amounts of oxybutynin are expected to be excreted into breast milk based on its physicochemical properties. The M/P ratio is unknown. Exercise caution when administering to a nursing woman. Monitor infant for anticholinergic effects (e.g., dry mouth, constipation, blurred vision). |
| Teratogenic Risk | Pregnancy Category B. There are no adequate and well-controlled studies in pregnant women. Animal studies at doses up to 1.6 mg/kg/day (approximately 10 times the maximum recommended human dose on a mg/m² basis) revealed no evidence of fetal harm. Use during pregnancy only if clearly needed. First trimester: No known increased risk of major malformations. Second and third trimesters: Potential for anticholinergic effects such as reduced fetal heart rate variability; consider monitoring fetal heart rate if used near term. |
■ FDA Black Box Warning
None
| Serious Effects |
Urinary retention; gastric retention; uncontrolled narrow-angle glaucoma; hypersensitivity to oxybutynin or any component of the product.
| Precautions | Angioedema (anaphylaxis/hypersensitivity reactions); exacerbation of myasthenia gravis; decreased gastrointestinal motility (risk of gastric retention); urinary retention; heat prostration (decreased sweating leading to fever/heatstroke); CNS effects (drowsiness, dizziness, confusion, especially in elderly); caution in patients with impaired renal or hepatic function; use with caution in patients with autonomic neuropathy, hiatal hernia with reflux esophagitis, ulcerative colitis, or hyperthyroidism. |
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| Fetal Monitoring | Monitor maternal vital signs for anticholinergic side effects (e.g., tachycardia, dry mouth, constipation, urinary retention). Fetal monitoring: no specific fetal monitoring required, but consider nonstress test or biophysical profile if used near term due to potential anticholinergic effects on fetal heart rate variability. |
| Fertility Effects | No specific studies on fertility effects in humans. In animal studies, oxybutynin did not impair fertility in rats at doses up to 20 mg/kg/day. No known clinically significant impact on female or male fertility. |