BRAND NAMES
 MECHANISM OF ACTION
Oxybutynin is a tertiary amine that exerts a direct antispasmodic effect on smooth muscle and acts as a competitive antagonist of acetylcholine (antimuscarinic) at post-ganglionic muscarinic receptors on the detrusor muscle of the bladder, resulting in relaxation of bladder smooth muscle. Although 5 muscarinic receptors have been identified (M1–M5), Oxybutynin has higher affinity for M1 and M3 receptor subtypes than for other muscarinic subtypes.
In patients with overactive bladder, characterised by involuntary bladder contractions and symptoms such as urgency, frequency, and nocturia, with or without urge incontinence, studies have demostrated that oxybutynin increases maximum urinary bladder capacity and increases the volume to first detrusor contraction. Oxybutynin thus decreases urinary urgency and the frequency of both incontinence episodes and voluntary urination.
Oxybutynin is a racemic (50:50) mixture of R- and S-isomers. Antimuscarinic activity resides predominantly in the R-isomer. A metabolite, desethyloxybutynin, has pharmacological activity similar to that of oxybutynin in vitro studies.
- Treatment of overactive bladder with symptoms of urge urinary incontinence, urgency, and frequency.
- Treatment of pediatric patients aged 6 years and older with symptoms of detrusor overactivity associated with a neurological condition (e.g., spina bifida).
- Extended Release Tablets (DITROPAN XL): must be swallowed whole with the aid of liquids, and must not be chewed, divided, or crushed.
- Adults: The recommended starting dose is 5 or 10 mg once daily. Dosage may be adjusted in 5 mg increments to achieve a balance of efficacy and tolerability (up to a maximum of 30 mg/day). In general, dosage adjustment may proceed at approximately weekly intervals.
- Pediatric Patients Aged 6 Years of Age and Older: The recommended starting dose of is 5 mg once daily. Dosage may be adjusted in 5 mg increments to achieve a balance of efficacy and tolerability (up to a maximum of 20 mg/day).
- Hypersensitivity to Oxybutynin
- Oxybutynin is contraindicated in patients with urinary retention, severe decreased gastrointestinal motility conditions, narrow-angle glaucoma and in patients who are at risk for these conditions.
 WARNINGS AND PRECAUTIONS
- Angioedema of the face, lips, tongue and/or larynx has been reported with oxybutynin. In some cases, angioedema occurred after the first dose. Angioedema associated with upper airway swelling may be life-threatening. If involvement of the tongue, hypopharynx, or larynx occurs, oxybutynin should be promptly discontinued and appropriate therapy and/or measures necessary to ensure a patent airway should be promptly provided.
- Oxybutynin should be administered with caution to patients with gastrointestinal obstructive disorders because of the risk of gastric retention
- Oxybutynin should be used with caution in patients who have gastroesophageal reflux and/or who are concurrently taking drugs (such as bisphosphonates) that can cause or exacerbate esophagitis
- Because Oxybutynin may produce drowsiness, somnolence, or blurred vision, patients should be advised to exercise caution when driving or using machinery
- Alcohol may enhance the drowsiness caused by anticholinergic agents such as oxybutynin
- The concomitant use of oxybutynin with other anticholinergic drugs or with other agents that compete for CYP3A4 enzyme metabolism may increase the frequency or severity of dry mouth, constipation and drowsiness.
- Oxybutynin may antagonize prokinetic therapies.
- Potent CYP3A4 inhibitors, such as itraconazole, erythromycin and clarithromycin may increase oxybutynin plasma concentrations.
 PREGNANCY AND LACTATION
- Pregnancy Category B (US). Reproduction studies with oxybutynin chloride in the mouse, rat, hamster, and rabbit showed no definite evidence of impaired fertility or harm to the animal fetus. The safety of Oxybutinin administration to women who are or who may become pregnant has not been established. Therefore, this drug should not be given to pregnant women unless, in the judgment of the physician, the probable clinical benefits outweigh the possible hazards.
- Nursing Mothers: It is not known whether oxybutynin is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when Oxybutinin is administered to a nursing woman.
 SIDE EFFECTS
The most frequently reported adverse effects include dry mouth, constipation, diarrhea, impaired urination, drowsiness (somnolence), blurred vision, dizziness, nervousness, headache and nausea.