From the Guidelines
Oxybutynin is an antimuscarinic agent that exerts its mechanism of action by competitively inhibiting the muscarinic acetylcholine receptors, specifically M1, M2, and M3 subtypes, in the bladder muscle and detrusor muscle, as indicated for treatment of detrusor overactivity in patients with neurogenic bladder 1.
Mechanism of Action
This inhibition results in a decrease in bladder contractions, thereby increasing bladder capacity and reducing symptoms of urgency and frequency.
Dosage
The typical oral dose of oxybutynin is 5-10 mg, administered two to three times daily, with a duration of action of approximately 6-10 hours, although a dose of 0.2 mg/kg oxybutynin orally given 3 times daily may be used for subjects noted to have a hostile bladder on urodynamic evaluation 1.
Administration Considerations
TDS preparations of oxybutynin may be offered if dry mouth is a concern with oral anti-muscarinics 1.
Key Points
- Oxybutynin is an antimuscarinic agent
- Inhibits muscarinic acetylcholine receptors
- Decreases bladder contractions
- Increases bladder capacity
- Reduces symptoms of urgency and frequency
- Typical oral dose: 5-10 mg, two to three times daily
- Duration of action: approximately 6-10 hours
From the FDA Drug Label
Oxybutynin chloride exerts a direct antispasmodic effect on smooth muscle and inhibits the muscarinic action of acetylcholine on smooth muscle. The mechanism of oxybutynin is through its antispasmodic and antimuscarinic effects, which relax bladder smooth muscle and inhibit the muscarinic action of acetylcholine. Key points about the mechanism include:
- Direct antispasmodic effect on smooth muscle
- Inhibition of muscarinic action of acetylcholine on smooth muscle
- Relaxation of bladder smooth muscle 2
From the Research
Mechanism of Oxybutynin
- Oxybutynin is a tertiary amine that undergoes extensive first-pass metabolism, with an active metabolite, N-desethyl oxybutynin, which exerts a significant portion of its effects 3
- The drug has both antimuscarinic and direct muscle relaxant effects, as well as local anesthetic actions 3
- Oxybutynin binds to M3 muscarinic receptors on the detrusor muscle of the bladder, preventing acetylcholinergic activation and relaxing the muscle 4
- The antimuscarinic action of oxybutynin is thought to be the primary mechanism by which it exerts its effects on the overactive bladder (OAB) 3
Pharmacological Effects
- Oxybutynin has been shown to have stereoselective antimuscarinic effects, with the R and S enantiomers exhibiting different levels of activity 5
- The drug has been found to inhibit carbachol-induced mucosal Cl-secretion in vitro, and to have local anesthetic activity in vivo 5
- Oxybutynin has been shown to decrease saliva output, which can lead to dry mouth, a common side effect of the drug 6
Clinical Use
- Oxybutynin is primarily indicated for the treatment of overactive bladder syndrome (OAB), and is thought to prevent involuntary bladder contractions and/or urgency by inhibiting the muscarinic receptors within the urothelium and detrusor muscle 7
- The drug is available in several formulations, including immediate- and extended-release tablets, transdermal patch and gel, vaginal ring, and suppository 7