OXYTROL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for OXYTROL (OXYTROL).
Oxytrol (oxybutynin) is a muscarinic receptor antagonist that inhibits the action of acetylcholine on muscarinic receptors, leading to relaxation of the detrusor muscle of the urinary bladder and reduction of urinary bladder contractions.
| Metabolism | Oxybutynin is extensively metabolized in the liver and gastrointestinal mucosa primarily via cytochrome P450 3A4 isoenzyme, with minor contributions from CYP3A5 and CYP2D6. |
| Excretion | Urine (primarily as metabolites, <1% unchanged), feces (minor). Approximately 80% renal, 20% biliary/fecal. |
| Half-life | Terminal elimination half-life approximately 7-10 hours (2-4 hours for immediate-release oxybutynin). Steady-state achieved within 2-3 days. |
| Protein binding | Oxybutynin: 91-93% bound to albumin; N-desethyloxybutynin: 99-100% bound to albumin. |
| Volume of Distribution | Oxybutynin: approximately 193 L (about 2.5-3 L/kg); distributes extensively into tissues, including salivary glands and CNS. |
| Bioavailability | Transdermal: approximately 90% (compared to IV); bypasses first-pass metabolism, avoiding high N-desethyloxybutynin metabolite levels. |
| Onset of Action | Transdermal: Approximately 4-6 hours (peak plasma concentrations achieved after 24-48 hours). |
| Duration of Action | Transdermal: 96 hours with twice-weekly application (continuous delivery maintains therapeutic levels). Clinical effect lasts as long as patch is worn. |
One 3.9 mg patch applied twice weekly (every 3-4 days) to the abdomen, hip, or buttock.
| Dosage form | FILM, EXTENDED RELEASE |
| Renal impairment | No dosage adjustment required for mild to moderate renal impairment (GFR 30-89 mL/min). For severe renal impairment (GFR <30 mL/min), maximum dose is one 3.9 mg patch twice weekly. Not studied in ESRD. |
| Liver impairment | No specific guidelines available; contraindicated in severe hepatic impairment (Child-Pugh class C). Use with caution in moderate impairment (Child-Pugh class B). |
| Pediatric use | Not approved for use in pediatric patients. |
| Geriatric use | Starting dose: one 3.9 mg patch twice weekly. No dose adjustment required solely based on age, but monitor for anticholinergic effects due to possible age-related renal or hepatic function decline. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for OXYTROL (OXYTROL).
| Breastfeeding | Oxybutynin is excreted into human milk in small amounts. The milk-to-plasma ratio (M/P) is not well defined but estimated to be <1. Based on limited data, breastfed infants are unlikely to experience adverse effects. However, due to the anticholinergic properties, monitoring for infant lethargy, irritability, or feeding difficulties is recommended. The American Academy of Pediatrics considers oxybutynin compatible with breastfeeding. |
| Teratogenic Risk | Oxytrol (oxybutynin transdermal) is classified as Pregnancy Category B. Animal studies have not demonstrated fetal risk, but adequate well-controlled studies in pregnant women are lacking. Based on available data, the risk of teratogenicity during the first trimester is considered low. Use during the second and third trimesters should be cautious due to potential anticholinergic effects on the fetus, including tachycardia and possible decreased gut motility, though no specific structural anomalies are reported. |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
["Urinary retention","Gastric retention","Uncontrolled narrow-angle glaucoma","Hypersensitivity to oxybutynin or any components of the product"]
| Precautions | ["May exacerbate or precipitate urinary retention, gastric retention, or narrow-angle glaucoma","Angioedema has been reported; discontinue if symptoms occur","Central nervous system effects including dizziness, somnolence, and confusion, especially in elderly patients","May decrease sweating, leading to heat prostration in hot environments","Use with caution in patients with myasthenia gravis, ulcerative colitis, or decreased gastrointestinal motility"] |
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| Fetal Monitoring | Monitor maternal vital signs for blood pressure changes and heart rate. Assess for signs of anticholinergic toxicity (dry mouth, blurred vision, constipation, tachycardia). In pregnant patients, include fetal heart rate monitoring if clinically indicated, especially if high doses are used or in the presence of other anticholinergic drugs. No specific ultrasound monitoring is required, but regular prenatal care should be maintained. |
| Fertility Effects | Animal studies suggest no significant adverse effects on fertility. In humans, oxybutynin may theoretically affect fertility due to anticholinergic effects on cervical mucus or ejaculation, but clinical data are lacking. Overall, the impact on fertility is minimal or absent. |