Extended-Release Oxybutynin

▲ Extended-release oxybutynin (Ditropan XL®1) uses an osmotic system (OROS®) to deliver a controlled amount of oxybutynin chloride into the gastrointestinal tract over a 24-hour period when taken once daily.▲ Oxybutynin binds to M3 muscarinic receptors on the detrusor muscle of the bladder, preventing acetylcholinergic activation and relaxing the muscle.▲ Mean peak plasma concentrations are lower with extended-release oxybutynin 15mg once daily than with conventional immediate-release oxybutynin 5mg taken 3 times daily. Relative bioavailabilities of parent drug and metabolite N-desethoxybutynin are 153 and 69%, respectively, for extended-release oxybutynin when compared with immediate-release oxybutynin.▲ In short (≤6 weeks) randomised, double-blind clinical trials of patients with detrusor instability, extended-release oxybutynin 5 to 30mg once daily significantly reduced the mean weekly number of urge incontinence episodes by 84 to 90%. Extended-release oxybutynin had similar efficacy to immediate-release oxybutynin.▲ Adverse events reported by patients taking extended-release oxybutynin were dose-related anticholinergic effects, most frequently dry mouth, somnolence, constipation, blurred vision and dizziness.▲ A large noncomparative study demonstrated that approximately two thirds of the patients prescribed extended-release oxybutynin for detrusor instability were still taking the medication 6 months later.