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. |
| Molecular Weight | 357.49 |
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 | Oxybutynin is classified as Pregnancy Category B in the US. Animal studies have not revealed evidence of teratogenicity, but adequate and well-controlled studies in pregnant women are lacking. Use only if clearly needed. |
| 2nd trimester | Same as first trimester: Category B. No known risk of fetal harm from animal studies, but human data insufficient. Consider risk-benefit. |
| 3rd trimester | Same as first trimester: Category B. Potential for uterine relaxation and prolongation of labor due to anticholinergic effects. Use with caution near term. |
Clinical note
Comprehensive clinical and safety monograph for OXYTROL (OXYTROL).
| Placental transfer | Oxybutynin is a tertiary amine and is expected to cross the placenta based on its molecular weight and lipophilic nature. Specific placental transfer studies are lacking, but based on pharmacokinetics, placental passage likely occurs. |
| Breastfeeding |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
Urinary retentionGastric retentionUncontrolled narrow-angle glaucomaHypersensitivity to oxybutynin or any componentSevere ulcerative colitisToxic megacolonMyasthenia gravis
| 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 |
| Food/Dietary | No significant food interactions reported. Avoid alcohol as it may increase drowsiness and risk of dizziness. |
Loading safety data…
| Oxybutynin is excreted into breast milk in small amounts. The relative infant dose is estimated to be <1% of the maternal weight-adjusted dose, considered low. Monitor infant for anticholinergic effects such as irritability, dry mouth, or constipation. Use with caution in nursing mothers, especially with preterm or compromised infants. |
| Lactation Rating | L2 (Probably Compatible) |
| 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. |
| 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. |
| Clinical Pearls | Apply to dry, intact skin on the abdomen, hip, or thigh; rotate application sites. Avoid application to areas with skin folds or recent shaving. Wash hands after handling the patch. Remove old patch before applying new one. |
| Patient Advice | Apply patch to clean, dry, hairless skin on abdomen, hip, or thigh. · Do not place patch on oily, irritated, or broken skin. · Rotate application site with each new patch. · Do not apply to the same site within 7 days. · Wash hands after handling the patch. · Remove old patch before applying a new one. · Avoid exposing patch to direct heat sources like heating pads. · Do not cut or alter the patch. |